One of the hardest things in studying either the cosmos or the fundamental structure of matter is wrapping your head around the sizes of things. Atoms and particles are so unfathomably small, and galaxies and galaxy clusters are just so unfathomably large.
Of course, the classic video "Powers of Ten" still does a great job of conveying these vastly different scales. I still love this - it is elegant and thought-provoking:
Also, it's worth checking out the interactive web version, based on the film.
An updated take on a similar story is this video from the American Museum of Natural History, which incorporates modern astronomical data into the illustration of the cosmos so that they more accurately represent what we know about what's out there.
Finally, a couple of students have sent me links to versions of this cool interactive graphic that shows the size scales of a whole bunch of things with a slider bar to move around. It's not made by scientists and has a couple of not-100%-accurate bits, but it more than makes up for that by having random weird and cool facts throughout. Definitely worth your time to play with for a while:
The Scale of the Universe version 2 by HTwins
Tuesday, February 21, 2012
Wednesday, February 15, 2012
Earth from the Space Station
My current pick for "best thing ever" is below... a compilation of NASA videos of the earth from the International Space Station, edited by Michael Konig.
This is just mind-blowing, isn't it? The timing of the compilation has been redone so it doesn't quite match the speed at which the space station travels. However, the original NASA videos do approximately represent the "real time" experience. View those at:
http://eol.jsc.nasa.gov/Videos/CrewEarthObservationsVideos/
Earth | Time Lapse View from Space, Fly Over | NASA, ISS from Michael König on Vimeo.
This is just mind-blowing, isn't it? The timing of the compilation has been redone so it doesn't quite match the speed at which the space station travels. However, the original NASA videos do approximately represent the "real time" experience. View those at:
http://eol.jsc.nasa.gov/Videos/CrewEarthObservationsVideos/
Imagining the Big Bang
There is a lovely story by Italo Calvino called "All at One Point" that I often assign in the beginning of my classes on cosmology. In it, a narrator discusses the Big Bang and the expansion of the universe as if he and many other characters had been present since the beginning. Describing the events of cosmic history in human terms highlights the absurdity of trying to picture the Big Bang at all. It's just impossible - what would it even mean to picture everything truly being at one point?
One of my students sent me the following link to a video art piece by Taras Hrabowsky:
First of all, this is just cool. But also, to me, this brings up some similar themes as the Calvino story (maybe because I just reread it again). Everything around us is part of a constantly changing and evolving cosmos. As we run the "movie" of cosmic history backwards and forwards in our heads, how can we not attempt to literally picture it?
One of my students sent me the following link to a video art piece by Taras Hrabowsky:
THINGPIT_HD from taras hrabowsky on Vimeo.
First of all, this is just cool. But also, to me, this brings up some similar themes as the Calvino story (maybe because I just reread it again). Everything around us is part of a constantly changing and evolving cosmos. As we run the "movie" of cosmic history backwards and forwards in our heads, how can we not attempt to literally picture it?
Wednesday, February 9, 2011
Magnetic Movies!
I love love love this animated piece by Ruth Jarman and Joe Gerhardt. In it, they imagine magnetic fields running wild over a laboratory. The audio comes from recordings of the magnetic field of the Sun. Spooky, beautiful, and definitely one the Best Things Ever.
For a different approach to magnetic field art, take a look at what people have been able to create using "ferrofluids." These fluids contain iron, and the iron will react to the presence of magnetic fields. Novel geometries of electromagnets can be used to control the ferrofluids and create truly bizarre sculptures. Here's an example piece from 2001 by Sachiko Kodama and Minako Takeno.
Magnetic Movie from Semiconductor on Vimeo.
For a different approach to magnetic field art, take a look at what people have been able to create using "ferrofluids." These fluids contain iron, and the iron will react to the presence of magnetic fields. Novel geometries of electromagnets can be used to control the ferrofluids and create truly bizarre sculptures. Here's an example piece from 2001 by Sachiko Kodama and Minako Takeno.
Earth's Magnetic Field
If you've ever played with a compass, you have interacted with the Earth's magnetic field. The Earth acts like a giant bar magnet. The magnetic field of the Earth benefits us because it shields the surface of the Earth from dangerous levels of radiation from space. We use it to navigate, as do some species of birds. But, somewhat amazingly, scientists still aren't completely sure where the magnetic field of the Earth comes from.
The basic explanation for the magnetic field of the Earth is something called the "dynamo effect." Molten iron in the core of the Earth carries electrical currents. Due to the spinning of the Earth, these currents tend to build up, and their resulting magnetic fields build up as well. Much the same way that electrical currents in a loop of wire can create an electromagnet, the Earth's magnetic field is born of loops of current inside the core. However, the exact details of this are still fuzzy. Making the whole question more complex is the evidence that the direction of the magnetic field of the Earth has reversed in the past. How exactly does that happen?
A couple of years ago, some scientists used a supercomputer to model the flipping of the Earth's magnetic fields. They visualized the output of their mathematical simulations using blue and orange lines to signify the field lines linked to the North and South poles of the Earth. Their simulations model how the field might flip, showing the strange state of the magnetic field in the middle of the transition. Below are images representing the Earth's field before and during a flip of polarity.
Check out the web page of the researchers who did this work. You can view an animation of the magnetic field flip in action here.
Finally, there is some recent evidence that perhaps this process of flipping happens really fast (well, fast on a geological timescale!) Odds are if you lived through one of these magnetic field flips you would never notice, but it is intriguing anyway! Here's a Science News article to find out more.
The basic explanation for the magnetic field of the Earth is something called the "dynamo effect." Molten iron in the core of the Earth carries electrical currents. Due to the spinning of the Earth, these currents tend to build up, and their resulting magnetic fields build up as well. Much the same way that electrical currents in a loop of wire can create an electromagnet, the Earth's magnetic field is born of loops of current inside the core. However, the exact details of this are still fuzzy. Making the whole question more complex is the evidence that the direction of the magnetic field of the Earth has reversed in the past. How exactly does that happen?
A couple of years ago, some scientists used a supercomputer to model the flipping of the Earth's magnetic fields. They visualized the output of their mathematical simulations using blue and orange lines to signify the field lines linked to the North and South poles of the Earth. Their simulations model how the field might flip, showing the strange state of the magnetic field in the middle of the transition. Below are images representing the Earth's field before and during a flip of polarity.
Finally, there is some recent evidence that perhaps this process of flipping happens really fast (well, fast on a geological timescale!) Odds are if you lived through one of these magnetic field flips you would never notice, but it is intriguing anyway! Here's a Science News article to find out more.
Tuesday, September 21, 2010
Multiple Universes vs. Higher Dimensions
I recently got an email out of the blue from a woman who was my childhood baby sitter. She has been reading popular physics books and was hoping that I could help with a lingering question: what
exactly is the difference between multiple universes and higher dimensions? This is a great question! As my answer grew longer and longer I realized maybe I should just turn it into a blog posting! Many of my students have asked me the same thing (see related earlier blog posts here and here), and it takes some work to explain.
In science fiction and in our casual vocabulary, "dimension" and "universe" may seem like similar or equivalent ideas. But, in current physical theory, they are really different. "Dimension" is a technical term with a very specific meaning that deals with the geometric properties of space. In contrast,
interestingly, "universe" has no single technical definition in physics, so it is often used by physicists to mean lots of different things. This vocabulary sloppiness creates a lot of confusion.
About Higher Dimensions
Most people are probably familiar with the idea that a piece of paper can be thought of as a "two dimensional"object or space. What does this mean? It means that if you want to specify the location of a dot on the piece of paper, you will need exactly two numbers to do so. These could be, for example, the distance of the dot from the left edge of the paper, and the distance of the dot from the bottom edge, in inches or centimeters or whatever. Any point on the paper can be described using a pair of these coordinates, which you might express as (x,y). Equivalently, there are two perpendicular
directions in which motion can take place within the space of the paper. An ant confined to the paper can move left and right and from the top to the bottom of the page, but can't move "in" or "out" of the paper.
"Dimension" to physicists always has the meaning expressed in these examples: it is an "axis" to the space you are talking about, or, equivalently, a direction that is available for the motion of objects in
the space. All positions in a one-dimensional space can be specified using just a single number (x), all positions in a two-dimensional space can be specified using two numbers (x,y), and all positions in our
familiar everyday three-dimensional space can be specified with three (x,y,z).
Since Einstein's work in the early 20th century, physicists have described our universe as a "four-dimensional" space (or "spacetime") in which time acts as a fourth dimension (or axis, or coordinate). This is just saying that to properly specify "positions" in our universe, you need to specify (x,y,z, t). We
can also write down equations that talk about spaces with even higher dimensions, which would require more coordinate axes to describe. Higher dimensional mathematics is something that math and science majors commonly encounter early in their undergraduate careers if not in high school, so it's not really even that exotic. What's new is the idea that higher dimensions might actually exist in physical space.
Relatively recently, the popular string theory (also called M-theory) has postulated that space in our universe might contain extra dimensions beyond our ordinary four. This is a very hard concept to get
your head around, because all of our mental mechanics for visualization are confined to ordinary three-dimensional space (even getting your head around four-dimensional space-time is tricky). Usually people try to explain this by an analogy, so I will do the same.
If you were the ant on a piece of paper, without the ability to look or move out of the paper, then visualizing or fully experiencing the third dimension would be impossible for you. If a person poked a finger through the piece of paper from above, your experience within your space would be of a barrier suddenly appearing at a particular location, but you would have no idea that the barrier you encountered was a two-dimensional "slice" of a larger three-dimensional object (the
finger). However, you might be able to infer the existence of higher dimensions by observing weird things happening in your space like the sudden appearance or disappearance of something that could be explained by, say, a three-dimensional finger poking its way through your space.
We too, like the ant, have no way of seeing "out" into higher dimensions if they exist. We can't directly perceive higher dimensions. But it is more than just that we lack some kind of "sense" for those
higher dimensions, the way that we lack the ability to hear a dog whistle or see infrared light. It's important to remember that our senses themselves derive from various forms of physical "detector" systems (our eyes, for example, are light detectors). All of those sensory detector systems play by the same physical rules that govern everything that is made out of atoms and molecules. So, for us to "sense" higher dimensions, it would have to be the case that systems made of ordinary atoms and molecules could move in those extra "directions." Apparently, they don't, or at least not in any obvious ways.
In fact, if the extra dimensions postulated by string theory or M-theory are there, they will be very hard for us to detect in any way even with the fanciest equipment out there. These extra dimensions really are supposed to be extra "directions" in the space around us, everywhere through the universe. But all of the physics of ordinary particles, atoms, and molecules is still operating in three spatial dimensions (plus time). So, finding any subtle clues of those extra dimensions is going to be really hard.
Multiple universes pop up as speculative possibilities in a lot of different physical theories. And, what's meant in each case is different. There's a semantics point here that is important: if in the word "universe" you include every phenomenon that is observable by scientists, then by definition science can only ever really know about "one universe." If you subscribe to that definition, then all "multiple universe" ideas are purely speculative. But, physical theories leave room for a lot of possibilities.
A few "multiple universe" ideas (not an exhaustive list):
One particular point of confusion is that the string theories that postulate higher dimensions also can provide explanations of the Big Bang and the origin of our universe in the context of many universes. Moreover, if you postulate extra dimensions, then you could imagine a "superspace" in which our three-dimensional "universe" is one of many. This is a hot topic of discussion right now. But, to wrap up the original question, the concept of a "dimension" and the concept of a "universe" are, even in this case, distinct and potentially independent. We could have the extra dimensions of space in our universe without there being other universes. Or, there could be other universes without any universe needing more than the ordinary three space dimensions and one time dimension. Dimensions are really just "directions" in space, while "universes" usually refer to some kind of totally separate space from the one accessible to the atoms, light, and particles we know.
These are pretty difficult concepts to express concisely, so I encourage followup questions!
exactly is the difference between multiple universes and higher dimensions? This is a great question! As my answer grew longer and longer I realized maybe I should just turn it into a blog posting! Many of my students have asked me the same thing (see related earlier blog posts here and here), and it takes some work to explain.
In science fiction and in our casual vocabulary, "dimension" and "universe" may seem like similar or equivalent ideas. But, in current physical theory, they are really different. "Dimension" is a technical term with a very specific meaning that deals with the geometric properties of space. In contrast,
interestingly, "universe" has no single technical definition in physics, so it is often used by physicists to mean lots of different things. This vocabulary sloppiness creates a lot of confusion.
About Higher Dimensions
Most people are probably familiar with the idea that a piece of paper can be thought of as a "two dimensional"object or space. What does this mean? It means that if you want to specify the location of a dot on the piece of paper, you will need exactly two numbers to do so. These could be, for example, the distance of the dot from the left edge of the paper, and the distance of the dot from the bottom edge, in inches or centimeters or whatever. Any point on the paper can be described using a pair of these coordinates, which you might express as (x,y). Equivalently, there are two perpendicular
directions in which motion can take place within the space of the paper. An ant confined to the paper can move left and right and from the top to the bottom of the page, but can't move "in" or "out" of the paper.
"Dimension" to physicists always has the meaning expressed in these examples: it is an "axis" to the space you are talking about, or, equivalently, a direction that is available for the motion of objects in
the space. All positions in a one-dimensional space can be specified using just a single number (x), all positions in a two-dimensional space can be specified using two numbers (x,y), and all positions in our
familiar everyday three-dimensional space can be specified with three (x,y,z).
Since Einstein's work in the early 20th century, physicists have described our universe as a "four-dimensional" space (or "spacetime") in which time acts as a fourth dimension (or axis, or coordinate). This is just saying that to properly specify "positions" in our universe, you need to specify (x,y,z, t). We
can also write down equations that talk about spaces with even higher dimensions, which would require more coordinate axes to describe. Higher dimensional mathematics is something that math and science majors commonly encounter early in their undergraduate careers if not in high school, so it's not really even that exotic. What's new is the idea that higher dimensions might actually exist in physical space.
Relatively recently, the popular string theory (also called M-theory) has postulated that space in our universe might contain extra dimensions beyond our ordinary four. This is a very hard concept to get
your head around, because all of our mental mechanics for visualization are confined to ordinary three-dimensional space (even getting your head around four-dimensional space-time is tricky). Usually people try to explain this by an analogy, so I will do the same.
If you were the ant on a piece of paper, without the ability to look or move out of the paper, then visualizing or fully experiencing the third dimension would be impossible for you. If a person poked a finger through the piece of paper from above, your experience within your space would be of a barrier suddenly appearing at a particular location, but you would have no idea that the barrier you encountered was a two-dimensional "slice" of a larger three-dimensional object (the
finger). However, you might be able to infer the existence of higher dimensions by observing weird things happening in your space like the sudden appearance or disappearance of something that could be explained by, say, a three-dimensional finger poking its way through your space.
We too, like the ant, have no way of seeing "out" into higher dimensions if they exist. We can't directly perceive higher dimensions. But it is more than just that we lack some kind of "sense" for those
higher dimensions, the way that we lack the ability to hear a dog whistle or see infrared light. It's important to remember that our senses themselves derive from various forms of physical "detector" systems (our eyes, for example, are light detectors). All of those sensory detector systems play by the same physical rules that govern everything that is made out of atoms and molecules. So, for us to "sense" higher dimensions, it would have to be the case that systems made of ordinary atoms and molecules could move in those extra "directions." Apparently, they don't, or at least not in any obvious ways.
In fact, if the extra dimensions postulated by string theory or M-theory are there, they will be very hard for us to detect in any way even with the fanciest equipment out there. These extra dimensions really are supposed to be extra "directions" in the space around us, everywhere through the universe. But all of the physics of ordinary particles, atoms, and molecules is still operating in three spatial dimensions (plus time). So, finding any subtle clues of those extra dimensions is going to be really hard.
About Multiple Universes
Multiple universes pop up as speculative possibilities in a lot of different physical theories. And, what's meant in each case is different. There's a semantics point here that is important: if in the word "universe" you include every phenomenon that is observable by scientists, then by definition science can only ever really know about "one universe." If you subscribe to that definition, then all "multiple universe" ideas are purely speculative. But, physical theories leave room for a lot of possibilities.
A few "multiple universe" ideas (not an exhaustive list):
- there exist wholly separate areas of three-dimensional space operating by the same basic physical laws as ours, but yet somehow not connected to ours.
- there exist many simultaneous versions of the universe in the same physical space but inaccessible to one another (this pops up mainly in many-worlds theories of quantum mechanics)
- there exist wholly separate physical entities in which the laws of physics may be completely different from the laws of physics in our observable universe.
One particular point of confusion is that the string theories that postulate higher dimensions also can provide explanations of the Big Bang and the origin of our universe in the context of many universes. Moreover, if you postulate extra dimensions, then you could imagine a "superspace" in which our three-dimensional "universe" is one of many. This is a hot topic of discussion right now. But, to wrap up the original question, the concept of a "dimension" and the concept of a "universe" are, even in this case, distinct and potentially independent. We could have the extra dimensions of space in our universe without there being other universes. Or, there could be other universes without any universe needing more than the ordinary three space dimensions and one time dimension. Dimensions are really just "directions" in space, while "universes" usually refer to some kind of totally separate space from the one accessible to the atoms, light, and particles we know.
These are pretty difficult concepts to express concisely, so I encourage followup questions!
Monday, September 6, 2010
Reactions to an interview with Simon Singh
Simon Singh is a science writer, and his historical account of the development of cosmology theory (the book Big Bang) is the central required text for my course on the subject at SAIC. Who knew that in addition to covering science history, he's in the business of taking on current pseudoscience?
Interestingly, Singh was recently sued by British chiropractors for publicly stating in one of his articles that the efficacy of chiropractic for certain ailments isn't supported by evidence. He didn't back down, and after spending a lot of his own money, he ended up winning the lawsuit. That definitely gives me a warm and fuzzy feeling, although it's depressing that this ended up in a lawsuit to begin with.
In this Wired Magazine interview with Singh, he brings up a few points about science in society that I find somewhat provocative, or at least intriguing. One of the key quotes from the interview is this: "you have to decide who you trust before you decide what to believe." So... why should you decide to trust scientists, as opposed to trusting, say, the anti-vaccine or no-global-warming folks?
I definitely do believe there are good reasons to trust scientists. I am willing to trust other scientists because I believe that (if they're being responsible anyway) what they're doing is making reasonable arguments and inferences based on evidence. I trust other scientists because implicitly I believe that if I were in their place, looking at the same evidence, I'd come to the same conclusions. But is that a reasonable assumption? And how much does my trust depend on the fact that I'm trained in science?
To me, a lot of science boils down to straightforward reasoning processes that I might even be tempted to call "common sense." So that's why it's particularly interesting to me that another quote from Singh's interview is "Science has nothing to do with common sense." Really? I can see his point (that sometimes the arguments of science are pretty subtle and convoluted), but his own Big Bang book does a pretty good job of making dramatic claims about the universe feel like common sense...
Lots to think about! I'll be curious to see what my students think.
Interestingly, Singh was recently sued by British chiropractors for publicly stating in one of his articles that the efficacy of chiropractic for certain ailments isn't supported by evidence. He didn't back down, and after spending a lot of his own money, he ended up winning the lawsuit. That definitely gives me a warm and fuzzy feeling, although it's depressing that this ended up in a lawsuit to begin with.
In this Wired Magazine interview with Singh, he brings up a few points about science in society that I find somewhat provocative, or at least intriguing. One of the key quotes from the interview is this: "you have to decide who you trust before you decide what to believe." So... why should you decide to trust scientists, as opposed to trusting, say, the anti-vaccine or no-global-warming folks?
I definitely do believe there are good reasons to trust scientists. I am willing to trust other scientists because I believe that (if they're being responsible anyway) what they're doing is making reasonable arguments and inferences based on evidence. I trust other scientists because implicitly I believe that if I were in their place, looking at the same evidence, I'd come to the same conclusions. But is that a reasonable assumption? And how much does my trust depend on the fact that I'm trained in science?
To me, a lot of science boils down to straightforward reasoning processes that I might even be tempted to call "common sense." So that's why it's particularly interesting to me that another quote from Singh's interview is "Science has nothing to do with common sense." Really? I can see his point (that sometimes the arguments of science are pretty subtle and convoluted), but his own Big Bang book does a pretty good job of making dramatic claims about the universe feel like common sense...
Lots to think about! I'll be curious to see what my students think.
Friday, June 25, 2010
Is the Universe Fundamentally Indeterministic?
My answer? Yes!!
What does that mean exactly? Yeah, mumble mumble mumble.
Backing up, I recently got a question from someone named Brian, who was commenting on the previous post. I love this question - it goes straight to one of the most profound philosophical ideas that physics leads us to ponder. The question was:
"I was just curious if you knew whether QM's being non-deterministic also rules out determinism at higher levels (like molecules, cells, etc)."
I'm not going to pretend that I can give a complete and totally satisfying answer to this question, but I will mumble at length about it! It is going to take a couple of steps to get to the actual question. So, here goes...me mumble my way through my own thoughts on the subject, in several steps
Quantum mechanics (the physics of very small systems like particles and atoms) is based on mathematical laws that are probabilistic in nature. For example, these laws can tell you the probability that if you measure the location of an electron in an atom, you will find it at a particular place. But, you can never predict exactly where the electron will be. Hence, quantum mechanics is not a deterministic theory (it does not enable you to make exact predictions of the properties of particle systems).
Now, the question is: is the probabilistic behavior fundamental, or is this just how we characterize what we observe because our theory is incomplete? Maybe if we knew more about electrons, and we could measure extra properties of the electron or the atom, we could predict the exact location at any time. Perhaps there are "hidden variables" describing the system of the electron in the atom, and our theory is just missing those.
This is a tempting way to rescue determinism, but it turns out to be impossible! In 1964, a guy named Bell used a little bit of logic to come up with a straightforward way to test whether hidden variables could work. Interestingly, you can test this experimentally without needing to specify what those hidden properties are. Sure enough, experimental tests of particle behaviors prove that quantum mechanics isn't missing anything - the probabilistic description is complete.
As I discovered this spring (when I taught a class in Randomness), trying to explain Bell's theorem is really hard! And, I should also mention that it's something that continues to be the subject of enormous discussion at the intersection between philosophy and physics (see, for example, the Stanford Encyclopedia of Philosophy article on Bell's Theorem). As well as I understand it, the experimental tests of Bell's theorem lead you inescapably to pick one of the three following conclusions:
1) The universe is "fundamentally random", such that the behavior of something like an electron in an atom does not follow deterministic rules (whether or not we know those rules)
2) The universe does follow deterministic rules, but the behavior of a single particle is influenced by the location/behavior of every other particle in the universe (hence, even in principle it would be impossible to make exact predictions anyway).
3) Basic, simple logic is wrong.
If 3 were true, a whole lot of other stuff would make no sense. But, depending on your philosophical preferences, you can pick option 1 or 2. I'm perfectly happy with option 1, hence my resounding "yes" at the top of this post.
Ok, so let's just go forward with the assumption that particle behaviors can only be predicted probabilistically, and not deterministically. Does that preclude deterministic behavior in macroscopic systems made up of many particles? Not necessarily.
The rules of quantum mechanics, including the fuzzy, probabilistic behavior, really only operate for small systems. Once you start to build up systems of many particles, their collective behavior becomes much more "classical" - governed by mathematics that is fully deterministic and allows exact prediction of behavior. Probing the transition from probabilistic rules to deterministic rules is something physicists are currently doing (see some of the material in this previous post, for example).
It's not like one set of rules just turns off at a particular size scale and the other set of rules turns on. Basically, the deterministic laws of classical physics (Newton's laws of motion, for example) can be viewed as only approximately true. But the larger the system, the closer the approximation gets to being pretty perfect. By the time you are operating with an object like a grain of dust, its behavior can be predicted with mathematics that is strictly deterministic, to a very very high accuracy.
So where does that leave the behavior of cells? REALLY INTERESTING QUESTION! I don't think anyone knows for sure, and a lot of the detailed physics of tiny biological systems is under study right now. Cells are large enough objects that in terms of their physics, they probably could be described with deterministic mathematics. But, at the same time, some of the processes within cells do take place at small enough scales that quantum mechanics could matter. So, this is science to actively watch for in the coming decades - is anyone able to figure out whether the probabilistic nature of quantum mechanics measurably translates to randomness in the behavior of cells?
There's one more step in how I think through all of this in my own head. The underlying question to me (whether or not Brian had this in mind) is whether human brains are ultimately deterministic or not. In other words, is every thought that I have a result of deterministic clockwork-like motions in my head? Or is some of the apparent spontaneity ultimately due to the fundamental randomness of the universe (a lovely thought, in my opinion)?
This would seem to be a straightforward either-or situation: either my brain is deterministic or it isn't. But, I'd like to point out that even if it is deterministic, that doesn't necessarily mean we will ever actually be able to accurately predict what a system as complex as the brain will do. This is not just a statement of the current limitations of science, but has to do with fundamental physics as well.
Even in fully deterministic systems, the interactions of many objects (particles, cells, etc.) can lead to a level of complexity such that the behavior appears to be random, and cannot ever be reduced in practice to deterministic laws. It may be the case that to exactly predict the behavior of one neuron (even in a deterministic brain) you would need to know the positions and motions of so many particles that it would take a computer the size of the universe just to store the numbers. If this is the case, the brain could still be "effectively" indeterministic - it could follow deterministic rules but involve such a level of complexity that no human instrument (present, or future, or even in science fiction) could ever determine what you're going to think next.
What does that mean exactly? Yeah, mumble mumble mumble.
Backing up, I recently got a question from someone named Brian, who was commenting on the previous post. I love this question - it goes straight to one of the most profound philosophical ideas that physics leads us to ponder. The question was:
"I was just curious if you knew whether QM's being non-deterministic also rules out determinism at higher levels (like molecules, cells, etc)."
I'm not going to pretend that I can give a complete and totally satisfying answer to this question, but I will mumble at length about it! It is going to take a couple of steps to get to the actual question. So, here goes...me mumble my way through my own thoughts on the subject, in several steps
Step 1: Quantum Mechanics and Determinism:
Quantum mechanics (the physics of very small systems like particles and atoms) is based on mathematical laws that are probabilistic in nature. For example, these laws can tell you the probability that if you measure the location of an electron in an atom, you will find it at a particular place. But, you can never predict exactly where the electron will be. Hence, quantum mechanics is not a deterministic theory (it does not enable you to make exact predictions of the properties of particle systems).
Now, the question is: is the probabilistic behavior fundamental, or is this just how we characterize what we observe because our theory is incomplete? Maybe if we knew more about electrons, and we could measure extra properties of the electron or the atom, we could predict the exact location at any time. Perhaps there are "hidden variables" describing the system of the electron in the atom, and our theory is just missing those.
This is a tempting way to rescue determinism, but it turns out to be impossible! In 1964, a guy named Bell used a little bit of logic to come up with a straightforward way to test whether hidden variables could work. Interestingly, you can test this experimentally without needing to specify what those hidden properties are. Sure enough, experimental tests of particle behaviors prove that quantum mechanics isn't missing anything - the probabilistic description is complete.
As I discovered this spring (when I taught a class in Randomness), trying to explain Bell's theorem is really hard! And, I should also mention that it's something that continues to be the subject of enormous discussion at the intersection between philosophy and physics (see, for example, the Stanford Encyclopedia of Philosophy article on Bell's Theorem). As well as I understand it, the experimental tests of Bell's theorem lead you inescapably to pick one of the three following conclusions:
1) The universe is "fundamentally random", such that the behavior of something like an electron in an atom does not follow deterministic rules (whether or not we know those rules)
2) The universe does follow deterministic rules, but the behavior of a single particle is influenced by the location/behavior of every other particle in the universe (hence, even in principle it would be impossible to make exact predictions anyway).
3) Basic, simple logic is wrong.
If 3 were true, a whole lot of other stuff would make no sense. But, depending on your philosophical preferences, you can pick option 1 or 2. I'm perfectly happy with option 1, hence my resounding "yes" at the top of this post.
Step 2: Macroscopic Determinism:
Ok, so let's just go forward with the assumption that particle behaviors can only be predicted probabilistically, and not deterministically. Does that preclude deterministic behavior in macroscopic systems made up of many particles? Not necessarily.
The rules of quantum mechanics, including the fuzzy, probabilistic behavior, really only operate for small systems. Once you start to build up systems of many particles, their collective behavior becomes much more "classical" - governed by mathematics that is fully deterministic and allows exact prediction of behavior. Probing the transition from probabilistic rules to deterministic rules is something physicists are currently doing (see some of the material in this previous post, for example).
It's not like one set of rules just turns off at a particular size scale and the other set of rules turns on. Basically, the deterministic laws of classical physics (Newton's laws of motion, for example) can be viewed as only approximately true. But the larger the system, the closer the approximation gets to being pretty perfect. By the time you are operating with an object like a grain of dust, its behavior can be predicted with mathematics that is strictly deterministic, to a very very high accuracy.
So where does that leave the behavior of cells? REALLY INTERESTING QUESTION! I don't think anyone knows for sure, and a lot of the detailed physics of tiny biological systems is under study right now. Cells are large enough objects that in terms of their physics, they probably could be described with deterministic mathematics. But, at the same time, some of the processes within cells do take place at small enough scales that quantum mechanics could matter. So, this is science to actively watch for in the coming decades - is anyone able to figure out whether the probabilistic nature of quantum mechanics measurably translates to randomness in the behavior of cells?
Step 3: "Effective" Indeterminism:
There's one more step in how I think through all of this in my own head. The underlying question to me (whether or not Brian had this in mind) is whether human brains are ultimately deterministic or not. In other words, is every thought that I have a result of deterministic clockwork-like motions in my head? Or is some of the apparent spontaneity ultimately due to the fundamental randomness of the universe (a lovely thought, in my opinion)?
This would seem to be a straightforward either-or situation: either my brain is deterministic or it isn't. But, I'd like to point out that even if it is deterministic, that doesn't necessarily mean we will ever actually be able to accurately predict what a system as complex as the brain will do. This is not just a statement of the current limitations of science, but has to do with fundamental physics as well.
Even in fully deterministic systems, the interactions of many objects (particles, cells, etc.) can lead to a level of complexity such that the behavior appears to be random, and cannot ever be reduced in practice to deterministic laws. It may be the case that to exactly predict the behavior of one neuron (even in a deterministic brain) you would need to know the positions and motions of so many particles that it would take a computer the size of the universe just to store the numbers. If this is the case, the brain could still be "effectively" indeterministic - it could follow deterministic rules but involve such a level of complexity that no human instrument (present, or future, or even in science fiction) could ever determine what you're going to think next.
Friday, June 18, 2010
Determinism and dish towels
In my class this spring on "randomness", I tried to convince my students that quantum mechanics (the physics of the very small) is inconsistent with a deterministic universe. The physics of this is difficult to explain without getting technical, and I am still working on a good explanation. For the purposes of this post, you may have to take my word for it that on a fundamental level, the behaviors of particles simply cannot be exactly predicted, even in principle. Fundamental physics is demonstrably not deterministic.
Despite the fact that this idea has been around for a long time, I'm discovering that today's college students still react with a lot of skepticism - there is still a deep desire to "rescue" determinism and to explain all observed randomness as merely apparent. Einstein is often quoted as being similarly uncomfortable with the claims of quantum mechanics. Famously, he said "God does not play dice with the universe". While you could probably spend a lot of time analyzing and critiquing Einstein's position, physicist Niels Bohr (one of the founders of quantum mechanics) had a pithy comeback: "Stop telling God what to do!"
Considering that what's at stake in the debate between Einstein and Bohr was (and is) one of the most fundamental philosophical questions you can ask about our universe, is it weird that nowadays you can wash and dry your dishes with Bohr's quote?
This lovely dish towel can be purchased here.
Despite the fact that this idea has been around for a long time, I'm discovering that today's college students still react with a lot of skepticism - there is still a deep desire to "rescue" determinism and to explain all observed randomness as merely apparent. Einstein is often quoted as being similarly uncomfortable with the claims of quantum mechanics. Famously, he said "God does not play dice with the universe". While you could probably spend a lot of time analyzing and critiquing Einstein's position, physicist Niels Bohr (one of the founders of quantum mechanics) had a pithy comeback: "Stop telling God what to do!"
Considering that what's at stake in the debate between Einstein and Bohr was (and is) one of the most fundamental philosophical questions you can ask about our universe, is it weird that nowadays you can wash and dry your dishes with Bohr's quote?
Wednesday, June 16, 2010
The Best Thing Ever
Lately, I have been reading a lot about the impact that Carl Sagan had on the public interest in (and understanding of) space. Every time I think about Sagan, I end up with "A Glorious Dawn" stuck in my head. I love this ridiculous video - everybody loves it! It's the best thing ever.
Saturday, May 1, 2010
Science and fashion?
One of the reasons I enjoy teaching science at an art and design school is because I believe science is such a rich source of ideas and inspiration for all forms of creative pursuits. I've started keeping my eyes open for different (and sometimes surprising) ways that scientific concepts or imagery appear in art, design, and even fashion.
The dress below is from the Lela Rose fall 2010 collection. When I ran across it, I read that the pattern for the fabric is inspired by Hubble Space Telescope 'images of lunar floors'. If I had to guess, I would have thought the images were from NASA space probes photographing Jupiter's moons, rather than Hubble, but what do I know?
The pattern looks to me like a re-imagining of the impact craters on moons as pools of water. Jupiter's moon Callisto is known for its craters and is what the pattern resembles most in terms of actual space images:
Image from http://photojournal.jpl.nasa.gov/target/Callisto
This gives me a random opportunity to make a plug for how cool the moons of Jupiter are. The four moons originally observed by Galileo (helping to lead to the sun-centered model of the solar system) are shown in a NASA "family portrait" below:
Image from http://photojournal.jpl.nasa.gov/target/Callisto
The other thing I thought about when I came across this dress was this post by one of my students to the Unstable Nucleus class blog.
The dress below is from the Lela Rose fall 2010 collection. When I ran across it, I read that the pattern for the fabric is inspired by Hubble Space Telescope 'images of lunar floors'. If I had to guess, I would have thought the images were from NASA space probes photographing Jupiter's moons, rather than Hubble, but what do I know?
The pattern looks to me like a re-imagining of the impact craters on moons as pools of water. Jupiter's moon Callisto is known for its craters and is what the pattern resembles most in terms of actual space images:
Image from http://photojournal.jpl.nasa.gov/target/Callisto
This gives me a random opportunity to make a plug for how cool the moons of Jupiter are. The four moons originally observed by Galileo (helping to lead to the sun-centered model of the solar system) are shown in a NASA "family portrait" below:
Image from http://photojournal.jpl.nasa.gov/target/Callisto
The other thing I thought about when I came across this dress was this post by one of my students to the Unstable Nucleus class blog.
Thursday, April 8, 2010
Multiple Multiverses
Two students wrote to me in the last week asking about two separate articles, both claiming "proof" of the existence of multiple universes. Oddly enough, the two articles are talking about completely different kinds of physics! Both articles are guilty of journalistic abuses of science, in my opinion - especially in their use of the word "proof". Yet they both report on reputable scientific research, so there is some validity to both ideas. Let's disentangle them a bit.
1. Macroscopic Quantum Mechanics and Multiverses.
(image from researcher Andrew Cleland, at UCSB), taken from a Science News article)
The first of the articles emailed to me this week has the provocative title "Freaky Physics Proves Multiple Universes Exist", from Fox News. This is a pretty exotic-sounding title.
The research reported in the Fox News article deals with quantum mechanics. Quantum mechanics is the physics of the very small, and it includes well-known oddities like the idea that a particle can be simultaneously in many places at once. The act of 'observing' the particle (which always involves light or other particles interacting with it) forces it to 'pick' which position it is in. These kinds of behaviors have been confirmed by many experiments, it just sounds especially strange and spooky when you try to describe quantum mechanics with ordinary language.
One of the long-standing explanations for weird quantum simultaneity involves a notion of many universes. These 'universes' are differentiated by multiple possible outcomes of every physical event. For example, if you flip a coin and it has a truly random chance of falling heads or tails, we would envision that it actually falls as heads in 'one universe' and as tails in 'another universe'. This helps with the quantum mechanics interpretation, because when we say that a particle behaves as if it's simultaneously in many places, what we mean is that there are simultaneously many universes in which it's doing different things.
This version of 'multiple universes' is not something you would think of as separate whole physical systems 'beyond' our universe of stars and galaxies and space. The quantum mechanical 'universes' are infinitely many simultaneous variations on everything that has ever happened.
So what's the article about? Basically, researcher Andrew Cleland and his collaborators have managed to create a tiny object (shown in the picture above) that displays the same kind of quantum fuzziness as individual particles do. Even though the object (like a little vibrating fin) is quite tiny, it is still HUGE compared to individual particles, so it is essentially macroscopic. The exciting thing is seeing that it shows the same properties of individual particles: it behaves as though it is simultaneously vibrating in different ways. This is a macroscopic manifestation of a particle property that is well know. It is also a step in the direction of better understanding possible technological applications of quantum mechanics.
Is this 'proof' of multiverses? No! The multiverse (multiple universe) idea is an interpretation of what we see in this experiment and what we have seen in many previous experiments. It's a valid interpretation, but there are others that don't involve multiple universes that are equally valid.
2. Dark Flow and Multiverses
(Hubble Space Telescope image of the Coma Cluster)
In my classes on cosmology, students often ask me whether there might be other universes somehow 'beyond' ours. Perhaps, universes containing different sets of stars and galaxies and beings. I usually answer that I don't know how to talk about 'beyond' the universe, since the universe contains all of space as we know it. But, then I say that it's always possible. Even so, the question of multiple universes doesn't become a significant question for science until those other universes have an observable impact on ours.
Well, that's exactly what some other researchers have recently claimed, as reported in a National Geographic article called "New Proof Unknown 'Structures' Tug at our Universe". This article is reporting on research by Alexander Kashlinsky and collaborators, in which they analyzed images of galaxy clusters (enormous groupings of many galaxies in clouds of gas and dark matter) and also images of the Cosmic Microwave Background. It's tricky to explain their technique in a few sentences, but the bottom line is that they believe that they have shown that a large number of galaxy clusters all seem to be moving in the same direction. This is called the "Dark Flow", which is just a cheesy name to designate the unexplained motion.
A number of scientists (including local supersmart grad student Ryan Keisler) have criticized the data analysis techniques that were used to find evidence for "Dark Flow". The Dark Flow research is not something straightforward to do - galaxy clusters are far too large for us to literally see them moving. It involves subtle calculations using a combination of different types of data, and there are a lot of places where things can go wrong. Other scientists analyzing the exact same data fail to see this effect, so it is fair to say there is serious doubt about the "Dark Flow" result!
However, if there were to be an observed "Dark Flow", it might have a pretty cool interpretation. One way to explain bulk motion of many large objects in the universe is to postulate something along the lines of gravity from beyond our observable universe (perhaps this counts as being from another universe?). I have no idea how this would work, but it's intriguing. Popular news articles like the one above are going way too far calling this 'proof' of multiple universes. However, unexplained large-scale gravitational pulls would be one potential way that other universes could affect ours, thus leading to new theories that extend beyond our own universe.
So, I wouldn't make too much of this. However, for all of my students who find multiple universes so fascinating, here's an example where they are being seriously discussed in science!
1. Macroscopic Quantum Mechanics and Multiverses.
(image from researcher Andrew Cleland, at UCSB), taken from a Science News article)
The first of the articles emailed to me this week has the provocative title "Freaky Physics Proves Multiple Universes Exist", from Fox News. This is a pretty exotic-sounding title.
The research reported in the Fox News article deals with quantum mechanics. Quantum mechanics is the physics of the very small, and it includes well-known oddities like the idea that a particle can be simultaneously in many places at once. The act of 'observing' the particle (which always involves light or other particles interacting with it) forces it to 'pick' which position it is in. These kinds of behaviors have been confirmed by many experiments, it just sounds especially strange and spooky when you try to describe quantum mechanics with ordinary language.
One of the long-standing explanations for weird quantum simultaneity involves a notion of many universes. These 'universes' are differentiated by multiple possible outcomes of every physical event. For example, if you flip a coin and it has a truly random chance of falling heads or tails, we would envision that it actually falls as heads in 'one universe' and as tails in 'another universe'. This helps with the quantum mechanics interpretation, because when we say that a particle behaves as if it's simultaneously in many places, what we mean is that there are simultaneously many universes in which it's doing different things.
This version of 'multiple universes' is not something you would think of as separate whole physical systems 'beyond' our universe of stars and galaxies and space. The quantum mechanical 'universes' are infinitely many simultaneous variations on everything that has ever happened.
So what's the article about? Basically, researcher Andrew Cleland and his collaborators have managed to create a tiny object (shown in the picture above) that displays the same kind of quantum fuzziness as individual particles do. Even though the object (like a little vibrating fin) is quite tiny, it is still HUGE compared to individual particles, so it is essentially macroscopic. The exciting thing is seeing that it shows the same properties of individual particles: it behaves as though it is simultaneously vibrating in different ways. This is a macroscopic manifestation of a particle property that is well know. It is also a step in the direction of better understanding possible technological applications of quantum mechanics.
Is this 'proof' of multiverses? No! The multiverse (multiple universe) idea is an interpretation of what we see in this experiment and what we have seen in many previous experiments. It's a valid interpretation, but there are others that don't involve multiple universes that are equally valid.
2. Dark Flow and Multiverses
(Hubble Space Telescope image of the Coma Cluster)
In my classes on cosmology, students often ask me whether there might be other universes somehow 'beyond' ours. Perhaps, universes containing different sets of stars and galaxies and beings. I usually answer that I don't know how to talk about 'beyond' the universe, since the universe contains all of space as we know it. But, then I say that it's always possible. Even so, the question of multiple universes doesn't become a significant question for science until those other universes have an observable impact on ours.
Well, that's exactly what some other researchers have recently claimed, as reported in a National Geographic article called "New Proof Unknown 'Structures' Tug at our Universe". This article is reporting on research by Alexander Kashlinsky and collaborators, in which they analyzed images of galaxy clusters (enormous groupings of many galaxies in clouds of gas and dark matter) and also images of the Cosmic Microwave Background. It's tricky to explain their technique in a few sentences, but the bottom line is that they believe that they have shown that a large number of galaxy clusters all seem to be moving in the same direction. This is called the "Dark Flow", which is just a cheesy name to designate the unexplained motion.
A number of scientists (including local supersmart grad student Ryan Keisler) have criticized the data analysis techniques that were used to find evidence for "Dark Flow". The Dark Flow research is not something straightforward to do - galaxy clusters are far too large for us to literally see them moving. It involves subtle calculations using a combination of different types of data, and there are a lot of places where things can go wrong. Other scientists analyzing the exact same data fail to see this effect, so it is fair to say there is serious doubt about the "Dark Flow" result!
However, if there were to be an observed "Dark Flow", it might have a pretty cool interpretation. One way to explain bulk motion of many large objects in the universe is to postulate something along the lines of gravity from beyond our observable universe (perhaps this counts as being from another universe?). I have no idea how this would work, but it's intriguing. Popular news articles like the one above are going way too far calling this 'proof' of multiple universes. However, unexplained large-scale gravitational pulls would be one potential way that other universes could affect ours, thus leading to new theories that extend beyond our own universe.
So, I wouldn't make too much of this. However, for all of my students who find multiple universes so fascinating, here's an example where they are being seriously discussed in science!
Sunday, April 4, 2010
Mini Big Bangs? Or "God Particles"? Or What?
It's a pretty exciting time in fundamental physics! The gigantic Large Hadron Collider (LHC), which is the world's most expensive and complex single machine, is finally smashing particles together as of last week.
The LHC is a particle accelerator that speeds up protons to insanely high energies and collides them with each other. The energy the protons carry is transformed into mass in these collisions, creating a spray of exotic particles. These particles are created out of energy according to Einstein's famous E-mc^2 equation, which says that energy and mass can be exchanged. The goal here is not to break up the protons and find out their structure, but to create new forms of matter that haven't yet been discovered.
Mini Big Bangs?
If you read any popular science news this week, you might have run into quotes like this one: "Physicists smashed sub-atomic particles into each other with record energy on Tuesday, creating thousands of mini-Big Bangs like the primeval explosion that gave birth to the universe 13.7 billion years ago." This quote is from a Reuters article by Robert Evans and Jonathan Lynn, published in the New York Times under the title "Mini Big Bangs Created in Cosmos Origins Project".
Is this true? Is this machine really making "mini big bangs"? Well, no, not exactly. The Big Bang is often mentioned in connection with LHC science, but that's not because it's capable of creating explosions that birth universes (as far as we know anyway!). One of the reasons high energy collisions are so interesting is because they approximate the conditions of the universe just a tiny fraction of a second after the Big Bang. The early universe was a hot, dense sea of particles, and the laws of physics under those conditions are something we still don't fully understand. We hope that by replicating those early-universe conditions momentarily in a collider like the LHC, we may be able to create deeper theories of the structure of matter that allow us to better understand the whole history of the universe. So, while each proton collision at the LHC approximates conditions shortly after the Big Bang, it isn't "creating thousands of mini-Big Bangs".
God Particles?
Some of the articles you'll see in the news describe the LHC as chasing the "God Particle". For example, here's an article from Time Magazine entitled "Why the Collider Matters: In Search of the God Particle". The term "God Particle" is a nickname for a particular particle whose existence is speculated but has not yet been proven. Its more formal name is the "Higgs Boson". Within the current physics theory that we have to describe the properties of particles and their interactions, the Higgs Particle plays a critical role. It is a hypothetical particle that is predicted, in some sense, by the mathematics that physicists have used to describe and model the behavior of the known particles in this fundamental theory, which is called the Standard Model. The Higgs is the "missing piece" in the Standard Model. It gets the name "God Particle" both because it is a critical component to the theory and because physicists have spent decades trying to discover its existence, so far to no avail.
If the Higgs particle exists, it is a very heavy particle (much heavier than a proton). Since energy and mass can be exchanged, you can potentially create very heavy particles in the laboratory in the context of very high energy collisions of other particles. This is why the LHC has a good chance of finally creating Higgs particles in a controlled environment in which they can be studied. If they are seen, it will be one of the major discoveries that physicists have spent the last couple of decades pursuing.
The LHC is a particle accelerator that speeds up protons to insanely high energies and collides them with each other. The energy the protons carry is transformed into mass in these collisions, creating a spray of exotic particles. These particles are created out of energy according to Einstein's famous E-mc^2 equation, which says that energy and mass can be exchanged. The goal here is not to break up the protons and find out their structure, but to create new forms of matter that haven't yet been discovered.
Mini Big Bangs?
If you read any popular science news this week, you might have run into quotes like this one: "Physicists smashed sub-atomic particles into each other with record energy on Tuesday, creating thousands of mini-Big Bangs like the primeval explosion that gave birth to the universe 13.7 billion years ago." This quote is from a Reuters article by Robert Evans and Jonathan Lynn, published in the New York Times under the title "Mini Big Bangs Created in Cosmos Origins Project".
Is this true? Is this machine really making "mini big bangs"? Well, no, not exactly. The Big Bang is often mentioned in connection with LHC science, but that's not because it's capable of creating explosions that birth universes (as far as we know anyway!). One of the reasons high energy collisions are so interesting is because they approximate the conditions of the universe just a tiny fraction of a second after the Big Bang. The early universe was a hot, dense sea of particles, and the laws of physics under those conditions are something we still don't fully understand. We hope that by replicating those early-universe conditions momentarily in a collider like the LHC, we may be able to create deeper theories of the structure of matter that allow us to better understand the whole history of the universe. So, while each proton collision at the LHC approximates conditions shortly after the Big Bang, it isn't "creating thousands of mini-Big Bangs".
God Particles?
Some of the articles you'll see in the news describe the LHC as chasing the "God Particle". For example, here's an article from Time Magazine entitled "Why the Collider Matters: In Search of the God Particle". The term "God Particle" is a nickname for a particular particle whose existence is speculated but has not yet been proven. Its more formal name is the "Higgs Boson". Within the current physics theory that we have to describe the properties of particles and their interactions, the Higgs Particle plays a critical role. It is a hypothetical particle that is predicted, in some sense, by the mathematics that physicists have used to describe and model the behavior of the known particles in this fundamental theory, which is called the Standard Model. The Higgs is the "missing piece" in the Standard Model. It gets the name "God Particle" both because it is a critical component to the theory and because physicists have spent decades trying to discover its existence, so far to no avail.
If the Higgs particle exists, it is a very heavy particle (much heavier than a proton). Since energy and mass can be exchanged, you can potentially create very heavy particles in the laboratory in the context of very high energy collisions of other particles. This is why the LHC has a good chance of finally creating Higgs particles in a controlled environment in which they can be studied. If they are seen, it will be one of the major discoveries that physicists have spent the last couple of decades pursuing.
Tuesday, March 23, 2010
The Raisin-Bread Universe
One of the most difficult ideas to convey in my classes on Cosmology is the notion that the universe can be expanding without there being a "center" that it is expanding away from. This comes up especially in the context of interpreting the original data taken by Edwin Hubble used to make the first observational arguments that the universe is expanding, and originated in a "Big Bang". Hubble (and his collaborator Humeson) discovered that all distant galaxies appear to be flying away from us, with the most distant ones flying away the fastest. This would seem to imply that all of the galaxies used to be closer together, but it would also seem to imply that we're at a special central location (otherwise, why is everything rushing away from here?).
The correct interpretation of Hubble's observations is that space itself is expanding. The galaxies aren't exactly moving, but the space in between them is growing over time. No matter what galaxy you happen to live in, the expansion of space itself makes it look as though all the rest of the galaxies are moving away from you.
The traditional analogy that is used in this scenario is the "raisin bread universe". Imagine that every galaxy is a raisin in a loaf of raisin bread. As the bread bakes, the whole loaf expands. The raisins all used to be closer together, but as the bread expands they all become more distant from each other. No matter what raisin you happen to be, it looks as though all the other raisins are running away. Same thing with the galaxies in the universe.
This is a pretty potent analogy for grasping what's meant by the expansion of the universe. Yet, it's rarely given a good visual form. Here are a few versions I could find:
The version above is from this website.
Here's an animated gif:
This one is from this webpage.
What do you think? Could you do better? Do these images work to convey the idea?
The correct interpretation of Hubble's observations is that space itself is expanding. The galaxies aren't exactly moving, but the space in between them is growing over time. No matter what galaxy you happen to live in, the expansion of space itself makes it look as though all the rest of the galaxies are moving away from you.
The traditional analogy that is used in this scenario is the "raisin bread universe". Imagine that every galaxy is a raisin in a loaf of raisin bread. As the bread bakes, the whole loaf expands. The raisins all used to be closer together, but as the bread expands they all become more distant from each other. No matter what raisin you happen to be, it looks as though all the other raisins are running away. Same thing with the galaxies in the universe.
This is a pretty potent analogy for grasping what's meant by the expansion of the universe. Yet, it's rarely given a good visual form. Here are a few versions I could find:
The version above is from this website.
Here's an animated gif:
This one is from this webpage.
What do you think? Could you do better? Do these images work to convey the idea?
Tuesday, March 9, 2010
Cosmic Scales
Two videos that give you a sense of the vastness of space and the smallness of the Earth in comparison. The first is a classic (Powers of Ten by Charles and Ray Eames). The second is a recent video by the American Museum of Natural History using actual astronomical data to show the observable universe.
Wednesday, March 3, 2010
Messages sent to deep space
Radio waves (including those used for broadcast television) are a form of light. As such, they travel at the fundamental 'speed of light' through space. Since we've been broadcasting radio waves for communication and entertainment for decades, this means that these signals are now tens of light years away from the Earth. Might they be the first thing any other intelligent life form in the galaxy discovers about us?
This is from "abstruse goose". I can't find any information about the author besides the signature (?) at the top. Here's where you can find the original: http://abstrusegoose.com/163
This is from "abstruse goose". I can't find any information about the author besides the signature (?) at the top. Here's where you can find the original: http://abstrusegoose.com/163
Old news that's still cool: the Voyager spacecraft
Voyager 1 and Voyager 2 were both launched in 1977. They've been traveling away from the Earth every since, and have passed beyond the orbit of Pluto. They are powered by "radioisotope thermoelectric generators", which use heat from the radioactive decay of Plutonium-238 to generate electricity. The plutonium will of course decay away over time, and the electrical generators will degrade in other ways, so the spacecraft will lose the ability to communicate with the Earth sometime around 2025.
A few crazy things to contemplate:http://voyager.jpl.nasa.gov/index.html
1) Voyager 1 is currently more than 10 billion miles away from the Earth. It took over 30 years for it to get that far, even traveling at crazy speeds (it's currently going about 38,000 miles an hour). Light travels the same distance in about 14 hours. At this rate, for a comparable spacecraft to go one lightyear would take over 17,000 years. And, the next nearest star to the sun is over 4 light years away. This just goes to show that practical interstellar space travel really is the stuff of science fiction for the time being. Check out the Voyager site at http://voyager.jpl.nasa.gov/index.html
2) Here's what the Earth looks like from millions of miles away. This picture was taken by Voyager 1 in 1990, and Carl Sagan dubbed it the "pale blue dot", and wrote a book about it. The bands across the image are sunlight interacting with the camera optics. The earth is the tiny blue dot you can barely see in the sunbeam on the right. More about this image can be found here.
3) If you were an alien, would you understand this? It's the cover on the "Golden Record" developed by Carl Sagan, meant to record significant sounds from the Earth in case extraterrestrial life ever discovers one of the Voyager spacecraft. The whole story of the Golden Record interesting as a time capsule of 1970s romanticism in science. The image comes from the Voyager site, here. A recent NPR radio program about Sagan and his wife and the Golden Record is found here. That NPR site has some great links, including some of the audio from the record itself.
A few crazy things to contemplate:http://voyager.jpl.nasa.gov/index.html
1) Voyager 1 is currently more than 10 billion miles away from the Earth. It took over 30 years for it to get that far, even traveling at crazy speeds (it's currently going about 38,000 miles an hour). Light travels the same distance in about 14 hours. At this rate, for a comparable spacecraft to go one lightyear would take over 17,000 years. And, the next nearest star to the sun is over 4 light years away. This just goes to show that practical interstellar space travel really is the stuff of science fiction for the time being. Check out the Voyager site at http://voyager.jpl.nasa.gov/index.html
2) Here's what the Earth looks like from millions of miles away. This picture was taken by Voyager 1 in 1990, and Carl Sagan dubbed it the "pale blue dot", and wrote a book about it. The bands across the image are sunlight interacting with the camera optics. The earth is the tiny blue dot you can barely see in the sunbeam on the right. More about this image can be found here.
3) If you were an alien, would you understand this? It's the cover on the "Golden Record" developed by Carl Sagan, meant to record significant sounds from the Earth in case extraterrestrial life ever discovers one of the Voyager spacecraft. The whole story of the Golden Record interesting as a time capsule of 1970s romanticism in science. The image comes from the Voyager site, here. A recent NPR radio program about Sagan and his wife and the Golden Record is found here. That NPR site has some great links, including some of the audio from the record itself.
Friday, February 19, 2010
The Galaxy Garden
What do you make of these?
These are images of the "Galaxy Garden", a project by artist Jon Lomberg in Kona, Hawaii. It's a garden designed to provide a scale model of the Milky Way, including the black hole at the center of the galaxy (modeled by a fountain). At this scale, our local solar system is much smaller than a single dot on a leaf. Weird? Goofy? Kinda fun?
These are images of the "Galaxy Garden", a project by artist Jon Lomberg in Kona, Hawaii. It's a garden designed to provide a scale model of the Milky Way, including the black hole at the center of the galaxy (modeled by a fountain). At this scale, our local solar system is much smaller than a single dot on a leaf. Weird? Goofy? Kinda fun?
Sunday, February 14, 2010
String Theory and Cosmology
Here, finally, is the promised second installment on the subject of string theory and cosmology.
In the previous post, I tried to give a relatively quick overview of what "string theory" is, more or less. Basically, it's a proposed re-envisioning of the fundamental structure of matter that would help to solve some of the outstanding questions in particle physics. So, what does this have to do with cosmology - the study of the physics and history of the universe as a whole?
If you're familiar with the idea of the Big Bang, you know that the early universe was a hot and dense place. So hot, and so dense, that the sorts of objects we see in the universe today (stars, galaxies, and ourselves) could not have existed. The whole universe was filled with a sea of interacting particles and radiation, for the first few hundred thousand years of its existence. As you imagine 'running the movie backwards' and ask about the earlier and earlier moments after the Big Bang, you have to imagine the universe getting hotter and hotter, and denser and denser, the closer you get to that initial moment.
There are limits to what telescopes, looking out farther and farther, can tell us about the hot, dense early universe. Instead, we turn to high-energy particle accelerators here on earth. By smashing particles into each other at higher and higher energies, we are able to momentarily mimic the conditions of the earliest universe. The hope is that as we learn more about the behavior and structure of matter at high energies, we will be able to understand what must have happened in the very earliest universe. This is why there are deep ties between cosmology and particle physics: to understand the early universe, we need to understand matter in extreme conditions. These extreme conditions are where current particle physics theory starts to break down: we don't know what mathematical formulas or physical models to apply for particles and their interactions at the highest energies that are relevant in upcoming accelerator experiments and in the Big Bang.
String theory definitely is one theory that could fit the bill. If it turns out to be true, then many physicists hope it will help to answer some outstanding puzzles in cosmology theory too. One of the biggest of these is the mystery of "inflation", which is a proposed period of rapid expansion in the first 10-36 seconds. While we have a number of indirect lines of evidence that inflation occurred, existing particle physics theory doesn't have a way to explain why it might have happened. Perhaps string theory will provide an answer?
So, to sum up: the primary reason that string theory is relevant for cosmology is that it could provide a more complete and fundamental description of matter applicable even to the extreme conditions of the Big Bang. A deeper theory of particle physics is definitely one of the major pieces needed for better understanding the history of the universe. There are other (somewhat more exotic) ways that string theory either might impact cosmological phenomena, or even suggest a different philosophical viewpoint on the nature of physical law (what I'm alluding to here is the so-called anthropic principle, which would take another blog post to describe). However, the main connection between string theory and cosmology is through the mysterious physics of the hot, dense early universe.
In the previous post, I tried to give a relatively quick overview of what "string theory" is, more or less. Basically, it's a proposed re-envisioning of the fundamental structure of matter that would help to solve some of the outstanding questions in particle physics. So, what does this have to do with cosmology - the study of the physics and history of the universe as a whole?
If you're familiar with the idea of the Big Bang, you know that the early universe was a hot and dense place. So hot, and so dense, that the sorts of objects we see in the universe today (stars, galaxies, and ourselves) could not have existed. The whole universe was filled with a sea of interacting particles and radiation, for the first few hundred thousand years of its existence. As you imagine 'running the movie backwards' and ask about the earlier and earlier moments after the Big Bang, you have to imagine the universe getting hotter and hotter, and denser and denser, the closer you get to that initial moment.
There are limits to what telescopes, looking out farther and farther, can tell us about the hot, dense early universe. Instead, we turn to high-energy particle accelerators here on earth. By smashing particles into each other at higher and higher energies, we are able to momentarily mimic the conditions of the earliest universe. The hope is that as we learn more about the behavior and structure of matter at high energies, we will be able to understand what must have happened in the very earliest universe. This is why there are deep ties between cosmology and particle physics: to understand the early universe, we need to understand matter in extreme conditions. These extreme conditions are where current particle physics theory starts to break down: we don't know what mathematical formulas or physical models to apply for particles and their interactions at the highest energies that are relevant in upcoming accelerator experiments and in the Big Bang.
String theory definitely is one theory that could fit the bill. If it turns out to be true, then many physicists hope it will help to answer some outstanding puzzles in cosmology theory too. One of the biggest of these is the mystery of "inflation", which is a proposed period of rapid expansion in the first 10-36 seconds. While we have a number of indirect lines of evidence that inflation occurred, existing particle physics theory doesn't have a way to explain why it might have happened. Perhaps string theory will provide an answer?
So, to sum up: the primary reason that string theory is relevant for cosmology is that it could provide a more complete and fundamental description of matter applicable even to the extreme conditions of the Big Bang. A deeper theory of particle physics is definitely one of the major pieces needed for better understanding the history of the universe. There are other (somewhat more exotic) ways that string theory either might impact cosmological phenomena, or even suggest a different philosophical viewpoint on the nature of physical law (what I'm alluding to here is the so-called anthropic principle, which would take another blog post to describe). However, the main connection between string theory and cosmology is through the mysterious physics of the hot, dense early universe.
Monday, January 18, 2010
An Introduction to String Theory
This post is prompted by a question from Daniel, one of my former students. He said he's been reading a bit about string theory lately and wondered whether there is any connection between string theory and cosmology. This is a very tough subject, but I'll try to give it a shot! I'll start off with a little bit of background on what we mean by "string theory" in this post, and then follow up later with how it connects to the physics of the universe as a whole.
One of the goals of physics research is to figure out the fundamental structure of matter. Most people are familiar with the idea that ordinary matter is made up of particles like protons, neutrons, and electrons. Go a little deeper and you find out that protons and neutrons are made up of even more fundamental particles called quarks. Decades of experimental research (largely using high-energy particle accelerators like Fermilab) have been used to build a theoretical model for the structure of matter, which goes by the very snazzy title of the "Standard Model".
The Standard Model is a theory that describes all the types of particles we know to exist, as well as the ways that they an interact. For example, electrons are fundamental particles that are described in the Standard Model. Their interactions with each other through the electric force are also encapsulated in the theory. The Standard Model has been fantastically successful, in that it is capable of predicting how particles will behave to very high accuracy. At the same time, this powerful theory is frustrating to physicists because we know it is still incomplete.
The biggest way that the Standard Model is incomplete is that it leaves out the force of gravity. It just doesn't work to stuff a description of gravitational forces into the mathematics of the Standard Model. On the one hand, gravity is so weak between individual particles that we can completely leave it out of the theory and still have a highly accurate model for describing how individual particles will interact. But on the other hand, if we want our fundamental theory to mathematically describe all the behavior of matter, how can we possibly leave out something as obvious as gravity?
Another way that the Standard Model is incomplete is that we suspect it's "missing" some fundamental particles. For example, we believe that the explanation for a number of weird phenomena in the universe is that there's some new particle out there that we're calling Dark Matter. We know Dark Matter can't be made up of any of the particles in the Standard Model, so clearly the Standard Model doesn't describe the complete picture.
(Just for your curiosity, if you want to know what it looks like to write down an equation that describes all the particles and their interactions, one version the Standard Model equation has been typed up an posted in pdf form here. Yikes!)
String theory is one postulated theory to replace the Standard Model (actually, there are many versions of string theory, so it's not strictly "one" theory). So far, we don't have evidence that string theory is correct, and a lot of physicists remain skeptical about it. String theory is a highly mathematical model that allows gravity to be described in the same framework as everything else we know about the behavior of matter. In order to do this, it plays fast and loose with the fundamental nature of space-time, with some exotic consequences. In particular, string theory requires the existence of many extra "spatial dimensions". It also requires the existence of a bunch of additional particles that we have never seen, and one of these as-yet-unknown particles might explain Dark Matter. Basically, these "requirements" for the existence of extra dimensions and extra particles are results of the mathematics: if the equations of string theory are true, then they must exist.
In string theory, all of the "fundamental" particles of the Standard Model (and also any new exotic fundamental particles we haven't discovered yet) actually have an even more fundamental common structure. All of these things we call "particles" are pictured as being vibrating "strings". The strings are the true fundamental constituents of all matter. Depending on how the strings are vibrating, they behave like particles with different properties (e.g. an electron, or a quark). Even the force of gravity can be understood in terms of vibrating strings. In particular, the strings associated with gravity vibrate and wiggle beyond our ordinary three-dimensional space into a bunch of extra spatial dimensions.
One idea people seem to find especially intriguing from string theory is the notion that there are "extra dimensions" to space. I've noticed that this concept often gets confused in people's minds with the idea of "multiple universes", so let me see if I can help you to distinguish these ideas.
The extra dimensions in string theory are difficult to talk about because they defy visualization by our human brains. Let's start by imagining a line drawn across a piece of paper. A line is something that you would describe mathematically as a "one-dimensional" object. This means that you can represent every position on the line using a single number, perhaps the distance from the edge of the paper. The whole piece of paper itself is a "two-dimensional" object: to specify a particular position on the piece of paper, you need to provide two numbers, like the distance from the top and the distance from the left edge. Another way of thinking of this is that if you were confined to a piece of paper, your motion would be limited to being in the up-down direction, the left-right direction, or some combination of these. Ordinary space that we live in has three dimensions: we can move in the up-down direction, the left-right direction, and a third "in-out" direction.
In string theory, there are extra "directions" for the motion of strings, that aren't visible to us. They exist everywhere, and if you were a string you could have access to them in addition to the regular three dimensions in which we ordinarily move around. But, that's a really different idea than a "different universe".
A good place to start to learn more is the PBS website associated with the program The Elegant Universe. Check it out here.
The Background: Why String Theory?
One of the goals of physics research is to figure out the fundamental structure of matter. Most people are familiar with the idea that ordinary matter is made up of particles like protons, neutrons, and electrons. Go a little deeper and you find out that protons and neutrons are made up of even more fundamental particles called quarks. Decades of experimental research (largely using high-energy particle accelerators like Fermilab) have been used to build a theoretical model for the structure of matter, which goes by the very snazzy title of the "Standard Model".
The Standard Model is a theory that describes all the types of particles we know to exist, as well as the ways that they an interact. For example, electrons are fundamental particles that are described in the Standard Model. Their interactions with each other through the electric force are also encapsulated in the theory. The Standard Model has been fantastically successful, in that it is capable of predicting how particles will behave to very high accuracy. At the same time, this powerful theory is frustrating to physicists because we know it is still incomplete.
The biggest way that the Standard Model is incomplete is that it leaves out the force of gravity. It just doesn't work to stuff a description of gravitational forces into the mathematics of the Standard Model. On the one hand, gravity is so weak between individual particles that we can completely leave it out of the theory and still have a highly accurate model for describing how individual particles will interact. But on the other hand, if we want our fundamental theory to mathematically describe all the behavior of matter, how can we possibly leave out something as obvious as gravity?
Another way that the Standard Model is incomplete is that we suspect it's "missing" some fundamental particles. For example, we believe that the explanation for a number of weird phenomena in the universe is that there's some new particle out there that we're calling Dark Matter. We know Dark Matter can't be made up of any of the particles in the Standard Model, so clearly the Standard Model doesn't describe the complete picture.
(Just for your curiosity, if you want to know what it looks like to write down an equation that describes all the particles and their interactions, one version the Standard Model equation has been typed up an posted in pdf form here. Yikes!)
What is String Theory?
String theory is one postulated theory to replace the Standard Model (actually, there are many versions of string theory, so it's not strictly "one" theory). So far, we don't have evidence that string theory is correct, and a lot of physicists remain skeptical about it. String theory is a highly mathematical model that allows gravity to be described in the same framework as everything else we know about the behavior of matter. In order to do this, it plays fast and loose with the fundamental nature of space-time, with some exotic consequences. In particular, string theory requires the existence of many extra "spatial dimensions". It also requires the existence of a bunch of additional particles that we have never seen, and one of these as-yet-unknown particles might explain Dark Matter. Basically, these "requirements" for the existence of extra dimensions and extra particles are results of the mathematics: if the equations of string theory are true, then they must exist.
In string theory, all of the "fundamental" particles of the Standard Model (and also any new exotic fundamental particles we haven't discovered yet) actually have an even more fundamental common structure. All of these things we call "particles" are pictured as being vibrating "strings". The strings are the true fundamental constituents of all matter. Depending on how the strings are vibrating, they behave like particles with different properties (e.g. an electron, or a quark). Even the force of gravity can be understood in terms of vibrating strings. In particular, the strings associated with gravity vibrate and wiggle beyond our ordinary three-dimensional space into a bunch of extra spatial dimensions.
Extra Dimensions?
One idea people seem to find especially intriguing from string theory is the notion that there are "extra dimensions" to space. I've noticed that this concept often gets confused in people's minds with the idea of "multiple universes", so let me see if I can help you to distinguish these ideas.
The extra dimensions in string theory are difficult to talk about because they defy visualization by our human brains. Let's start by imagining a line drawn across a piece of paper. A line is something that you would describe mathematically as a "one-dimensional" object. This means that you can represent every position on the line using a single number, perhaps the distance from the edge of the paper. The whole piece of paper itself is a "two-dimensional" object: to specify a particular position on the piece of paper, you need to provide two numbers, like the distance from the top and the distance from the left edge. Another way of thinking of this is that if you were confined to a piece of paper, your motion would be limited to being in the up-down direction, the left-right direction, or some combination of these. Ordinary space that we live in has three dimensions: we can move in the up-down direction, the left-right direction, and a third "in-out" direction.
In string theory, there are extra "directions" for the motion of strings, that aren't visible to us. They exist everywhere, and if you were a string you could have access to them in addition to the regular three dimensions in which we ordinarily move around. But, that's a really different idea than a "different universe".
More on String Theory
A good place to start to learn more is the PBS website associated with the program The Elegant Universe. Check it out here.
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