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!