Other Life in the Multiverse?

by Paul Gilster on February 25, 2010

What conditions would you say are ‘congenial to life’? For physicist Robert Jaffe and colleagues at MIT, the phrase refers to places where stable forms of hydrogen, carbon and oxygen can exist. Jaffe explains why:

“If you don’t have a stable entity with the chemistry of hydrogen, you’re not going to have hydrocarbons, or complex carbohydrates, and you’re not going to have life. The same goes for carbon and oxygen. Beyond those three we felt the rest is detail.”

It’s an important issue in Jaffe’s work because he wants to see whether other universes could harbor life. We know that slight changes to the laws of physics would disrupt the evolution of the universe we live in. The strong nuclear force, for example, could have been just a bit stronger, or weaker, and stars would have been able to produce few of the elements needed to build planets. Remove the electromagnetic force and light would not exist, nor would atoms and chemical bonds.

Nudging Nature’s Parameters

Run through the constants of nature and you’ll find many that have to show precise values for life as we know it to have formed. Thus the idea that there may be not one but many universes, each with its own laws, and the thought that we happen to occupy a universe where the conditions that make life a possibility managed to fall into place.

Anthropic reasoning like this — things have to be this way because otherwise we couldn’t be here to think about all this — suggests that multitudes of universes exist, a multiverse in which almost all the universes would be devoid of life and, indeed, matter as we know it. Jaffe is interested in finding out whether universes with different physical laws might not be so inhospitable to life after all. His team focused on universes with nuclear and electromagnetic forces that allow atoms to exist. Another stipulation: Universes that allowed stable forms of hydrogen, carbon and oxygen.

Then it became a matter of playing with nature’s building blocks. Take quarks: In our universe, the ‘down’ quark is roughly twice as heavy as the ‘up’ quark, so that neutrons are 0.1 percent heavier than protons. Jaffe’s team lightened up the down quark so that protons were up to one percent heavier than neutrons. According to this modeling, hydrogen would no longer be stable, but the heavier isotopes deuterium and tritium would be. Carbon-14 could exist and so would a form of oxygen. It’s a different universe than ours, but the models say life could emerge in it.

Other quark variations, including one where the ‘up’ and ‘strange’ quarks have roughly the same mass, unlike in our universe, produced atomic nuclei made up of neutrons and a hyperon called the ‘sigma minus,’ which would replace protons. The fact that we have a reasonable understanding about quark interactions makes them useful for studies of this kind, but changing other physical laws is even trickier business.

Into a ‘Weakless’ Universe

Nonetheless, Lawrence Berkeley National Laboratory researchers have modeled universes that lack one of the four fundamental forces of ours. Without the weak force big bang nucleosynthesis — turning groups of four protons into helium 4 nuclei of two protons and two neutrons — would not have been possible. But when the team at LNBL removed the weak nuclear force in their models, they were able to tweak the other three forces to compensate. Stable elements could form in this universe as well.

Note what’s happening here. Rather than changing a single constant, the LBNL researchers tweaked several. After all, in a multiverse that can keep spewing out universe after universe, all combinations would seem to be possible and you can keep trying until you get it right. This Scientific American article by Alejandro Jenkins (MIT) and Gilad Perez (now at the Weizmann Institute) gets into the specifics:

In the weakless universe, the usual fusing of protons to form helium would be impossible, because it requires that two of the protons convert into neutrons. But other pathways could exist for the creation of the elements. For example, our universe contains overwhelmingly more matter than antimatter, but a small adjustment to the parameter that controls this asymmetry is enough to ensure that the big bang nucleosynthesis would leave behind a substantial amount of deuterium nuclei. Deuterium, also known as hydrogen 2, is the isotope of hydrogen whose nucleus contains a neutron in addition to the usual proton. Stars could then shine by fusing a proton and a deuterium nucleus to make a helium 3 (two protons and one neutron) nucleus.

But would these stars be anything like what we are familiar with? The article continues:

Such weakless stars would be colder and smaller than the stars in our own universe. According to computer simulations by astrophysicist Adam Burrows of Princeton University, they could burn for about seven billion years—about the current age of our sun—and radiate energy at a rate that would be a few percent of that of the sun.

A Strange But Living Universe

A strange place, this ‘weakless’ universe. Supernova explosions of the kind that synthesize and distribute heavy elements in our universe would not occur, at least not from the same causes, but a different kind of supernova caused by accretion rather than gravitational collapse would be possible, allowing elements to seed interstellar space. A planet like ours circling one of the weakless stars would need to be six times closer to the Sun to stay habitable. And check this out:

Weakless Earths would be significantly different from our own Earth in other ways. In our world, plate tectonics and volcanic activity are powered by the radioactive decay of uranium and thorium deep within Earth. Without these heavy elements, a typical weakless Earth might have a comparatively boring and featureless geology—except if gravitational processes provided an alternative source of heating, as happens on some moons of Saturn and Jupiter.

Chemistry, on the other hand, would be very similar to that of our world. One difference would be that the periodic table would stop at iron, except for extremely small traces of other elements. But this limitation should not prevent life-forms similar to the ones we know from evolving. Thus, even a universe with just three fundamental forces could be congenial to life.

Accounting for the Cosmological Constant

Still tantalizing is the cosmological constant, a measure of the amount of energy found in empty space. The discovery of the continuing acceleration of the universe’s expansion has brought ‘dark energy’ into the picture, implying a cosmological constant that is positive as well as minute, allowing the universe to form structure. It’s a constant that seems fine-tuned to a remarkable degree, and as the article notes, “…the methods our teams have applied to the weak nuclear force and to the masses of quarks seem to fail in this case, because it seems impossible to find congenial universes in which the cosmological constant is substantially larger than the value we observe. Within a multiverse, the vast majority of universes could have cosmological constants incompatible with the formation of any structure.”

All of this is almost joyously theoretical, basing itself on a theory of inflation that conceives of small pockets of spacetime that inflate so rapidly that it is impossible to travel between them. Inflation is highly regarded but not definitively understood, but different values for the constants of nature in the universes it produces seem like a reasonable conjecture. And the cosmological constant itself is an example of fine-tuning on such a scale that it may require the existence of a multiverse to give us a rational explanation for how we lucked into this one.

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{ 68 comments }

Ron S March 9, 2010 at 22:56

Eniac,

No problem with the speculation, just so that I’m clear on the landscape we’re discussing. I’m sure it’s no surprise that I also enjoy speculation. Unfortunately, this sort of discussion requires some thinking and I’m a bit pressured for time right now, so please excuse me if I’m somewhat brief. It’s terrible how life gets in the way of the fun stuff.

Eniac: If “sufficient number” is written as “all possible”, I think you will agree that indeed “our” universe has to appear, unless you want to claim ours is impossible.”

If we assume there is a “generator” function for universes, it may have terms of both free and dependent parameters, and one or more of these will also include a random variable. I’m assuming that randomness of some variety is in there since without it we are left with a far more tightly constrained set of possible universes (deterministic by some program), and which is therefore immune to statistical analysis. That function produces the operating parameters of a universe, including: foundational physical laws locked within a false that, when it decays, deterministically or randomly (or a combination of both) into an initial state, condensation of physical laws, and entropy. More or less.

It is interesting that there is some real theoretical and empirical work going on today to see how far back into and beyond the inflation phase of our universe we can see, by correctly identifying durable chains of evidence that we can observe now.

Even if very successful, I am doubtful that we can learn anything about that foundational generator function, or even if there is one, or if it’s a one-shot affair or repeating. Maybe Tegmark talks to some of this, but I don’t know. I’ve had one of his papers on my desktop for months now, and have not had the time to delve into it.

But whatever that function can be, I agree with you that it must be capable of generating our universe (duh). The open question is what else it can generate, and if can do so, will it.

Smolin’s program relies on black holes to spawn new spacetimes that deterministically seed the generator function, constraining its degrees of freedom enough that there can be only small steps in the initial state and laws of daughter universes. He proposes no mechanism by which this information is passed forward.

Eniac: “Or, take general relativity. The formula governing all of space-time can be written down on a napkin, but it took many years (and presumably a lot of napkins and envelopes) to find the first non-trivial solution, and it doesn’t look pretty. In each of these cases, the ensemble of all possible solutions is simpler than a particular solution.”

To be honest, I don’t find this very deep. Differential equations and their ilk are notorious for being immune to analytical solutions, especially those with non-linearity, such as are found in GR. I don’t believe there’s any meaning to be found in this general field of mathematics, except to force mathematicians to run to their computers and do some real work by building numerical algorithms. (Confession: I once did this sort of thing, although I am not a real mathematician.)

Eniac: “…it is much easier to assume that they are all equally valid, that there is no such thing as a “reality finger” pointing to one particular instance. In fact, postulating such a finger would be pretty close to postulating a deity.”

Agreed!

Regarding Boltzman brains… I made a pretty large mistake in my previous comment, which you seemed to pick up on even though you didn’t tear into it. I was a bit careless because I was in a hurry. Let me try again.

I didn’t intend to directly compare the cases of a minimal Boltzman brain with another, more extreme statistical fluctuation that generates our present universe, as it is today. I was trying to trying to use that minimal case as a model to compare generated universes, from a false vacuum birth, that would give rise to one with just one minimally-intelligent species in the entire universe to one that is more fecund, and then to knock down that comparison as absurd. That is, the Boltzman brain approach to universe generation suffers from the same fine tuning problem as the Rare Earth hypothesis. Instead I wanted to argue that the generator function (which I elaborated upon earlier) does not suffer from that statistical constraint, and therefore there is no reason to believe that we find ourselves in a universe that can generate life (us), but only us; there is no reason to believe that the free and random parameter of the generator function suffers from that fine tuning problem (founded on statistical improbability), and therefore if the universe can support development of intelligent life it is highly improbable that it would do so only once, and it is more likely that it would be widespread in the universe.

My apologies for the long sentences!

Eniac March 10, 2010 at 11:37

Ron,

I (with Tegmark, AFAIK) don’t think there needs to be a generator. The ensemble is the set of all possible universes. Period. It needs only to be defined, not generated. Similar to the set of all integers, which is easily defined but can never be generated in its entirety. Take two times the number of Planck time intervals since the Big Bang. It is an integer, it could not possibly ever have been generated, but it is nevertheless just as “real” as any other integer.

That also means there needs to be no random variables. If, following Everett and Wheeler, both branches of any decision have equal right to claim “existence”, there is never anything truly random. No “collapse” of wave functions. Time evolution is described completely by the time evolution operator (U=e^iHt, I think, with H the Hamiltonian) on the universal wave function. This operator is unitary, meaning that phase space volume is maintained and time evolution completely reversible. Randomness and the direction of time are illusions generated by our restricted point of view (we “see” only those things causally connected to us by the Hamiltonian) . The other branch does not “collapse”, it simply disappears from view. God does not roll dice, after all.

Finally, you said it twice, and I did not directly comment, but you seem to think that the existence of our universe is somehow less probable than a spontaneously generated Boltzman brain. I claim the opposite. The universe is vastly more likely, because it is described by simple laws and all the steps finally leading to brains are all fairly plausible. Even in combination they still yield a much higher probability than that of a “naked” Boltzman brain. This is why we we have bodies, and see so many other people, other species, other planets, other stars, and other galaxies around us. All these things have origins in common with our own. They are all needed to make our existence plausible.

I do not think that ETI fall into this category, though, because they would not share origins with us. This is certainly debatable, though. Maybe they do. I am starting to change my mind about this… It depends on whether the origin of life is somehow “more difficult” than the origins of stars, planets, etc. If it isn’t, I suppose there should be other ETIs on other star systems just as there are other stars in other galaxies.

Ron S March 11, 2010 at 0:35

Eniac,

I think this discussion, while interesting, is starting to wind down. Maybe this is a good thing since this article is about to slip off Paul’s main page! Then again, maybe I’m just getting a little frustrated that we are not really able to see eye to eye on many points, or there is at least a sprinkling of miscommunication between us. Nevertheless, on to my reply to your previous comment.

First, I have no idea what it is that defines the parameter space of “all possible universes” you discuss. Perhaps Tegmark discusses this but, as I said, I haven’t read his work yet. Yet without some program telling us how it is that all possible combinations of parameters (independent axes) are each instantiated as a universe, each with its particular physical laws and other state data, I can make nothing of it. Perhaps this is a fault peculiar to myself but this seems to me like so much vague arm waving. You don’t like my presentation of generators — ok, fine — but I will insist that *something* has to trigger and seed a generator to instantiate each universe. We disagree on this point, obviously.

Eniac: “…you seem to think that the existence of our universe is somehow less probable than a spontaneously generated Boltzman brain.”

No I don’t! Apparently I failed, twice, to communicate this fact to you. My words seem clear enough to me, but perhaps that’s only because I know what it is I was attempting to say. I tried to draw an analogy, but definitely not compare, Boltzman brains of any complexity with universes that evolve from a distinct initial, ordered state. I then tried to tie the latter to the concept of a generating function, and then compare the relative probabilities of universes so created.

As you should have noted by now, I see no explanatory power at all in multiverses covering a full spectrum of laws and states, just as I see no explanatory power in Everett’s interpretation of QM where our universe (with its set of laws and states) is a tree of distinct universes which branches for every conceivable wave function collapse. It is a useful idea for writing some entertaining sci-fi novels, but the explanatory power is poor and, in my judgment, the cost is much too high.

Using either or both versions of multiverses (universe types, and all possible outcomes from the origin of this one) is one way that has been proposed to ground the anthropic principle. I don’t see it; it’s just too extreme. However, there will have to be a resolution to the meaning of probability within our physics, and the roll it may have played in determining our own universe’s physical laws. Is it fundamental or not, and if so then why? It’s an open question.

Eniac March 11, 2010 at 14:29

Ron,

I think we do understand things pretty much the same way, with the exception that I am not able to effectively convey my central, admittedly entirely philosophical point: Multiverses are awkward and uncomfortable as long as you try to include them in your concept of “reality”, somehow. They are natural and simplifying, on the other hand, if you permit that there is no such thing as reality. That there is no distinction between that which is possible, and that which is real. That everything that is possible is equally “real”. That there is no existence other than in the mathematical sense.

Yes, I know it sounds nutty, and I will desist now …

Ron S March 11, 2010 at 15:53

I really don’t see why you would want to rank various types of reality. As far as I’m concerned, this universe — including you, me and this blog — are entirely real. Whatever the substrate may be, we are here. How would you propose to compare this reality to another to judge their essences of reality? Nutty or not, this is a dead end.

One last thought. Mathematics is logic. So when you point to mathematics as a substrate, you are indirectly stating that (formal) logic is the substrate.

Eniac March 11, 2010 at 17:51

I really don’t see why you would want to rank various types of reality. As far as I’m concerned, this universe — including you, me and this blog — are entirely real. Whatever the substrate may be, we are here. How would you propose to compare this reality to another to judge their essences of reality?

That’s just what I am saying. Let’s not look for an “essence of reality”, because there is none.

One last thought. Mathematics is logic. So when you point to mathematics as a substrate, you are indirectly stating that (formal) logic is the substrate.

I suppose so. More concretely, though, my thought was that the universe is real in the same sense the Mandelbrot set is, no more, no less. No different types of reality at all, just that one type.

Eniac March 12, 2010 at 0:19

There we go, we have fallen off the front page :-)

Ron S March 12, 2010 at 0:41

Eniac: “…my thought was that the universe is real in the same sense the Mandelbrot set is…”

If you are unfamiliar with mathematical philosophy, it is very possible you would enjoy reading up on the alternative definitions of mathematical “reality”: Platonism, Formalism and Constructivism. From your various statements you would appear to be a Platonist. A Platonist regards mathematical objects as part of an objective reality, and doing mathematics is an act of discovery.

In contrast, a Formalist sees mathematics as no more than a sort of game played with axioms, theorems and definitions, with no bearing whatever on reality. A Constructivist sees mathematics as a pure human invention, which if not constructed does not exist, but is a useful tool.

Near as I can tell, I’m uncommitted to all mathematical philosophies.

Eniac March 12, 2010 at 13:47

I am not very familiar with mathematical philosophy, as I am sure you can tell, but it appears that I am indeed a Platonist. Except, perhaps, instead of defining mathematics in terms of reality, I like it the other way around. I have no doubt that mathematics is objective, but whether it is reality depends on your definition of reality. The easy way out is to define reality in terms of mathematics. Then it all fits together.

Oh, the beauty of it!

PS: Look at the Mandelbrot Set. Zoom in and fly around. Visit some of its places. Then tell me this is not an act of discovery.

ljk January 31, 2011 at 5:37

A Physicist Explains Why Parallel Universes May Exist

January 24, 2011

Our universe might be really, really big — but finite. Or it might be infinitely big.

Both cases, says physicist Brian Greene, are possibilities, but if the latter is true, so is another posit: There are only so many ways matter can arrange itself within that infinite universe. Eventually, matter has to repeat itself and arrange itself in similar ways. So if the universe is infinitely large, it is also home to infinite parallel universes.

Does that sound confusing? Try this:

Think of the universe like a deck of cards.

“Now, if you shuffle that deck, there’s just so many orderings that can happen,” Greene says. “If you shuffle that deck enough times, the orders will have to repeat. Similarly, with an infinite universe and only a finite number of complexions of matter, the way in which matter arranges itself has to repeat.”

Greene, the author of The Elegant Universe and The Fabric of the Cosmos, tackles the existence of multiple universes in his latest book, The Hidden Reality: Parallel Universes and the Deep Laws of the Cosmos.

Full article here:

http://www.npr.org/2011/01/24/132932268/a-physicist-explains-why-parallel-universes-may-exist

ljk May 23, 2011 at 21:34

http://www.technologyreview.com/blog/arxiv/26787/

Multiverse = Many Worlds, Say Physicists

Two of the most bizarre ideas in modern physics are different sides of the same coin, say string theorists

kfc 05/23/2011

The many worlds interpretation of quantum mechanics is the idea that all possible alternate histories of the universe actually exist. At every point in time, the universe splits into a multitude of existences in which every possible outcome of each quantum process actually happens.

So in this universe you are sitting in front of your computer reading this story, in another you are reading a different story, in yet another you are about to be run over by a truck. In many, you don’t exist at all.

This implies that there are an infinite number of universes, or at least a very large number of them.

That’s weird but it is a small price to pay, say quantum physicists, for the sanity the many worlds interpretation brings to the otherwise crazy notion of quantum mechanics. The reason many physicists love the many worlds idea is that it explains away all the strange paradoxes of quantum mechanics.

For example, the paradox of Schrodinger’s cat–trapped in a box in which a quantum process may or may not have killed it– is that an observer can only tell whether the cat is alive or dead by opening the box.

But before this, the quantum process that may or may not kill it is in a superposition of states, so the cat must be in a superposition too: both alive and dead at the same time.

That’s clearly bizarre but in the many worlds interpretation, the paradox disappears: the cat dies in one universe and lives in another.

Let’s put the many world interpretation aside for a moment and look at another strange idea in modern physics. This is the idea that our universe was born along with a large, possibly infinite, number of other universes. So our cosmos is just one tiny corner of a much larger multiverse.

Today, Leonard Susskind at Stanford University in Palo Alto and Raphael Bousso at the University of California, Berkeley, put forward the idea that the multiverse and the many worlds interpretation of quantum mechanics are formally equivalent.

But there is a caveat. The equivalence only holds if both quantum mechanics and the multiverse take special forms.

Let’s take quantum mechanics first. Susskind and Bousso propose that it is possible to verify the predictions of quantum mechanics exactly.

At one time, such an idea would have been heresy. But in theory, it could be done if an observer could perform an infinite number of experiments and observe the outcome of them all.

But that’s impossible, right? Nobody can do an infinite number of experiments. Relativity places an important practical limit on this because some experiments would fall outside the causal horizon of others. And that would mean that they couldn’t all be observed.

But Susskind and Bousso say there is a special formulation of the universe in which this is possible. This is known as the supersymmetric multiverse with vanishing cosmological constant.

If the universe takes this form, then it is possible to carry out an infinite number of experiments within the causal horizon of each other.

Now here’s the key point: this is exactly what happens in the many worlds interpretation. At each instant in time, an infinite (or very large) number of experiments take place within the causal horizon of each other. As observers, we are capable of seeing the outcome of any of these experiments but we actually follow only one.

Bousso and Susskind argue that since the many worlds interpretation is possible only in their supersymmetric multiverse, they must be equivalent. “We argue that the global multiverse is a representation of the many-worlds in a single geometry,” they say.

They call this new idea the multiverse interpretation of quantum mechanics.

That’s something worth pondering for a moment. Bousso and Susskind are two of the world’s leading string theorists (Susskind is credited as the father of the field), so their ideas have an impeccable pedigree.

But what this idea lacks is a testable prediction that would help physicists distinguish it experimentally from other theories of the universe. And without this crucial element, the multiverse interpretation of quantum mechanics is little more than philosophy.

That may not worry too many physicists, since few of the other interpretations of quantum mechanics have testable predictions either (that’s why they’re called interpretations).

Still, what this new approach does have is a satisfying simplicity– it’s neat and elegant that the many worlds and the multiverse are equivalent. William of Ockham would certainly be pleased and no doubt, many modern physicists will be too.

Ref: http://arxiv.org/abs/1105.3796: The Multiverse Interpretation of Quantum Mechanics

ljk November 28, 2011 at 12:51

Links to articles and programs on the multiverse and skepticism on the concept:

http://www.math.columbia.edu/~woit/wordpress/?p=4194

The multiverse theory has the wonderful appeal that if you are a screwup in this universe, at least maybe in several other ones you are a hero. But whether any of this is true remains to be seen.

ljk December 3, 2011 at 1:29

Spacetime ‘Branes: The Multiverse

by David Darling

Today I have the pleasure of hosting my friend David Darling, an astronomer and well-known science writer, who will update us on the multiverse. Dr. Darling has written many books of popular science, including Life Everywhere: The Maverick Science of Astrobiology (in which he mentions my views on Rare Earth and the Anthropic Principle). He also maintains a much-visited website, The Worlds of David Darling that contains The Internet Encyclopedia of Science. His latest book, Megacatastrophes!: Nine Strange Ways the World Could End, his second collaboration with Dirk Schulze-Makuch, will appear next spring.

The multiverse, or theory of many universes, is very much in the news right now because some recent work strongly suggests that it might be true. The basic, mind-boggling idea is that “out there” is more than just the bubble of space-time we happen to live in – what we call the Universe. There are trillions and trillions (and trillions and trillions…) of other universes. Don’t even bother trying to imagine them all or your head might explode.

Surprisingly, the word “multiverse” has been around for a long time. It was coined way back in 1895 by the American philosopher William James, although he probably had something quite different in mind than what modern scientists are talking about.

Full article here:

http://www.starshipnivan.com/blog/?p=5495

ljk December 3, 2011 at 1:32

Wednesday, November 30, 2011

Microphysics and Cosmophysics in the 1930s

Abstract:

By 1930, at a time when the new physics based on relativity and quantum theory had reached a state of consolidation, problems of a foundational kind began to abound. Physicists began to speak of a new “crisis” and envisage a forthcoming “revolution” of a scale similar to the one in the mid-1920s.

The perceived crisis was an issue not only in microphysics but also in cosmology, where it resulted in ambitious cosmophysical theories that transcended the ordinary methods of physics. The uncertain cognitive situation was, in some circles, associated to the uncertain political and moral situation.

Did the problems of foundational physics demand a revolution in thinking that somehow paralleled the political revolutions of the time?

I argue that although such ideas were indeed discussed in the 1930s, they were more rhetoric than reality. With the benefit of hindsight one can see that the perceived crisis was only temporary and not significantly related to social or ideological developments in the decade.

“Visions of Revolutions: Microphysics and Cosmophysics in the 1930s” by Helge Kragh

http://philosophyofscienceportal.blogspot.com/2011/11/microphysics-and-cosmophysics-in-1930s.html

ljk January 25, 2012 at 0:24

Physicists Hope to Catch Neutrons in the Act of Jumping from Our Universe to Another

By Clay Dillow

Posted 01.23.2012 at 2:26 pm

The notion of multiple universes is one that cosmologists like to theorize about but generally don’t relish proving, mainly because doing so would be very difficult. But a team of researchers that showed a few years ago how matter might travel between our universe and others now think they ought to be able to observe this phenomenon in action using existing technology, lending credence to the multiverse theory. All they need is a neutron bottle, some neutrons, and a year.

Full article here:

http://www.popsci.com/science/article/2012-01/physicists-hope-catch-neutrons-act-jumping-our-universe-another

ljk January 30, 2012 at 10:58

http://www.technologyreview.com/blog/arxiv/27517/

How Neutrons Might Escape Into Another Universe

The leap from our universe to another is theoretically possible, say physicists. And the technology to test the idea is available today

kfc 01/23/2012

The idea that our universe is embedded in a broader multidimensional space has captured the imagination of scientists and the general population alike.

This notion is not entirely science fiction. According to some theories, our cosmos may exist in parallel with other universes in other sets of dimensions. Cosmologists call these universes braneworlds. And among that many prospects that this raises is the idea that things from our Universe might somehow end up in another.

A couple of years ago, Michael Sarrazin at the University of Namur in Belgium and a few others showed how matter might make the leap in the presence of large magnetic potentials. That provided a theoretical basis for real matter swapping.

Today, Sarrazin and a few pals say that our galaxy might produce a magnetic potential large enough to make this happen for real. If so, we ought to be able to observe matter leaping back and forth between universes in the lab. In fact, such observations might already have been made in certain experiments.

The experiments in question involve trapping ultracold neutrons in bottles at places like the Institut Laue Langevin in Grenoble, France, and the Saint Petersburg Institute of Nuclear Physics. Ultracold neutrons move so slowly that it is possible to trap them using ‘bottles’ made of magnetic fields, ordinary matter and even gravity.

One reason to do this is to measure how quickly the neutrons decay by beta emission. So physicists measure the rate at which the neutrons hit the bottle walls and how quickly this drops.

There are two processes at work here: the rate of neutron decay and the rate at which neutrons escape from the bottle. So in the case of an ideal bottle, the rate of decay should be equal to the beta decay rate. But the bottles are not ideal so the rate of decay is always faster.

That leaves open the possibility that there might be a third process at work: that some of the extra decay might be the result of neutrons jumping from our universe to another.

So Sarrazin and co have used the measured decay rates to place an upper limit on how often this can happen.

Their conclusion is that the probability of a neutron jumping ship is smaller than about one in a million.

That doesn’t really say anything about whether matter swapping actually takes place. Only that if it does, it doesn’t happen very often.

However, Sarrazzin and co also say it should be straightforward to take better data that places stricter limits.

According to their theoretical work, a change in the gravitational potential should also influence the rate of matter swapping. So one idea is to carry out a neutron trapping experiment that lasts for a year or more, allowing the Earth to complete at least one orbit of the Sun.

In that time, the gravitational potential changes in a way that should influence the rate of matter swapping. Indeed, there ought to be an annual cycle. “If one can detect such a modulation it would be a strong indication that matter swapping really occurs,” they say.

That would be one of the biggest and most controversial discoveries in modern physics and one that is possible with technologies available today.

Anyone got an old neutron bottle lying around and a bit of spare time on their hands?

Ref: http://arxiv.org/abs/1201.3949: Experimental Limits On Neutron Disappearance Into Another Braneworld

ljk February 22, 2012 at 17:05

The latest from Not Even Wrong on the multiverse concept. The comments to this piece are also quite enlightening:

http://www.math.columbia.edu/~woit/wordpress/?p=4447

ljk May 22, 2012 at 12:37

Not Even Wrong aka Peter Woit comments on Brian Greene’s new article about the Multiverse in Newsweek magazine:

http://www.math.columbia.edu/~woit/wordpress/?p=4715

To quote:

The article is pretty uniformly a promotional piece for multiverse mania, although buried fairly deep in the piece is something a bit more skeptical:

Because the proposal is unquestionably tentative, we must approach it with healthy skepticism and invoke its explanatory framework judiciously.

Imagine that when the apple fell on Newton’s head, he wasn’t inspired to develop the law of gravity, but instead reasoned that some apples fall down, others fall up, and we observe the downward variety simply because the upward ones have long since departed for outer space. The example is facetious but the point serious: used indiscriminately, the multiverse can be a cop-out that diverts scientists from seeking deeper explanations. On the other hand, failure to consider the multiverse can place scientists on a Keplerian treadmill in which they furiously chase answers to unanswerable questions.

Which is all just to say that the multiverse falls squarely in the domain of high-risk science. There are numerous developments that could weaken the motivation for considering it, from scientists finally calculating the correct dark-energy value, or confirming a version of inflationary cosmology that only yields a single universe, or discovering that string theory no longer supports a cornucopia of possible universes. And so on.

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