New Physics Complications Lend Support to Multiverse Hypothesis

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"New Physics Complications Lend Support to Multiverse Hypothesis"

From Scientific American:


On an overcast afternoon in late April, physics professors and students crowded into a wood-paneled lecture hall at Columbia University for a talk by Nima Arkani-Hamed, a high-profile theorist visiting from the Institute for Advanced Study in nearby Princeton, N.J. With his dark, shoulder-length hair shoved behind his ears, Arkani-Hamed laid out the dual, seemingly contradictory implications of recent experimental results at the Large Hadron Collider in Europe.

“The universe is inevitable,” he declared. “The universe is impossible.”

The spectacular discovery of the Higgs boson in July 2012 confirmed a nearly 50-year-old theory of how elementary particles acquire mass, which enables them to form big structures such as galaxies and humans. “The fact that it was seen more or less where we expected to find it is a triumph for experiment, it’s a triumph for theory, and it’s an indication that physics works,” Arkani-Hamed told the crowd.

However, in order for the Higgs boson to make sense with the mass (or equivalent energy) it was determined to have, the LHC needed to find a swarm of other particles, too. None turned up.

With the discovery of only one particle, the LHC experiments deepened a profound problem in physics that had been brewing for decades. Modern equations seem to capture reality with breathtaking accuracy, correctly predicting the values of many constants of nature and the existence of particles like the Higgs. Yet a few constants — including the mass of the Higgs boson — are exponentially different from what these trusted laws indicate they should be, in ways that would rule out any chance of life, unless the universe is shaped by inexplicable fine-tunings and cancellations.

Bolded by me. While certainly not enough to definitively prove the existence of a multiverse, from the way the article reads it does sound like the Standard Model has some holes in it. I personally defer judgement to those on this forum whose knowledge of such things vastly exceed my own. Any thoughts?
 

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  • #2
marcus
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That was a colloquium talk Arkani-Hamed gave at Columbia on 29 April. It was commented on by Peter Woit, who attended, in his blog of 30 April
http://www.math.columbia.edu/~woit/wordpress/?p=5747
So then there was some discussion by a number of people at the blog.

And then again on 24 May Natalie Wolchover gave a journalistic account at the Simons Foundation website titled Is Nature Unnatural? https://www.simonsfoundation.org/features/science-news/is-nature-unnatural/
The Simons website has a department called "Simons Science News" and she writes for that.
Her article was picked up by SciAm and reposted online 1 June.

On 25 May, after Natalie Wolchover's 24 May post, Peter Woit commented again on Arkani-Hamed colloquium, and the coverage in Simons News. That led to a bunch more discussion at his blog:
http://www.math.columbia.edu/~woit/wordpress/?p=5946&cpage=1#comments
So all this controversy and fuss seems to have been a little over a month ago.
The title of Peter Woit's blog post of 25 May was
The "Unnatural" Standard Model

If you want to see some informed discussion you might have a look there. Turns out the message in this case is not exactly new. Nima has been singing the same song for a while and Woit gives links to earlier presentations by him. The recently reported LHC results didn't occasion a revolutionary new departure AFAICS. But you can check out the discussion at
http://www.math.columbia.edu/~woit/wordpress/?p=5946&cpage=1#comments
and see what other people had to say and what arguments developed over what points.
 
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  • #3
marcus
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Multiverse is an awfully vague word, though.
You can distinguish between two types of multiverse vision, the type which can serve to excuse the failure of string research to come up with one distinguished version of physics and the type of multiplicity which does not excuse or motivate acceptance of string ideas.

For example consider a scenario that led to the proliferation of a whole bunch of totally unconnected universes all with the same laws of physics and natural constant as we have. that would be no comfort to string folks. You would still face the question "why are these laws what they are?" and "why is the cosmological constant and the various masses what they are?"

But consider a scenario that you could imagine leads to a whole bunch with all different physical constants! Then physicists could think of themselves as excused from having to explain why physics is the way it is. It could just be an ACCIDENT! That would be a great comfort to string folks. Leonard Susskind started promoting that idea in 2003.
In that year partly because of a paper called the KKLT (by his colleagues at stanford) people in the business began to suspect string approach would never arrive at a TOE, explaining why the physics of our world, that we see and live in, is how it is. KKLT got an estimate that string "predicts" some 10100 different versions of physics with different sets of constants.

That could be seen as a disaster but suppose there actually are all those different versions of physics and we are just in the one we are in by accident! Then the theory is a SUCCESS! Or one can imagine that anyway. And one is excused from the traditional hard job physicists have always had of explaining why this world is this way.

So that's the background. Two types of "Multiverse" fantasy. One type is of no aid or comfort to string theorists---it is kind of neutral or irrelevant. Other big bang events may have occurred unrelated to ours with no suggestion that together they form a larger ensemble that instantiates the String Landscape of versions of physics. We disregard them and keep focused on what we got, which we want to explain.
And the other type, which some devoted string folks are still promoting after 10 years (beginning with the 2003 papers by KKLT and by Susskind).

Interestingly the string leadership (that organizes the annual conference) froze out the Landscape Multiverse starting in 2008. Strings 2008 (Geneva) did not have any Landscape Multiverse papers. Susskind was not invited to give a paper and he did not attend. David Gross one of the leaders most adamantly opposed to the Multiverse excuse and the whole Landscape business, has always been the lead speaker or the person who gives the "outlook" talk at the end. It has been a pretty consistent pattern ever since 2008. I think he has referred to it as "giving up". That is giving up on the job which he hopes the theory will be able to do.
 
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from the way the article reads it does sound like the Standard Model has some holes in it.
There's nothing wrong with the standard model. The LHC is seeing 100% standard model and nothing but standard model; the Higgs was the last missing piece and it turned up.

All the other particles that were supposed to turn up are "beyond-standard-model", and they were expected, as part of elaborate schemes that would explain why the Higgs is light and how it stays light. There are two issues. First, the elementary particles get their mass from the "VEV" (energy density) of the Higgs field, and the VEV is quite small compared to what it could be. This is the "hierarchy problem". Second, although the Higgs is light, it ought to look heavy because of virtual particles, unless all the effects just balance miraculously. This is the "finetuning problem", and supersymmetry was supposed to solve it by introducing new particles that would make the virtual effects cancel in a more natural way. But the new particles aren't being seen.
 
  • #5
marcus
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That's the background. So when you hear someone talking Multiverse to wide audience, or thru a journalist to the public that's the question to ask. Is that person trying to let theoretical physicists (string of the Susskind school in particular) off the hook?

I agree with what Mitchell just said but I want to continue the thought.

When you hear them, ask if they are wringing their hands and making a big fuss about some of the numbers in the Standard Model. "Oh dear these numbers are so BIG or else so TINY! Oh dear we will never be able to explain these numbers!!! There must be a multiverse and these numbers simply must be an ACCIDENT! Oh good, then we don't have to explain them. Our theory giving a lot of different answers, instead of a bug, that is actually a feature! A theory of nature is supposed to give a lot of different answers, get it?, because there is a MULTIVERSE :biggrin:
 
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  • #6
Physics Monkey
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One thing I find (probably due to my own predilections) a bit silly about discussions of naturalness, multiverse, etc. is the little attention paid to perspectives from condensed matter physics as well as non-perturbative issues.

I want to emphasize at the start that I'm not suggesting that people haven't thought about these things before, just that maybe we should ponder them more often.

For example:

Assuming holographic duality is correct (which it almost certainly is), the "landscape" of string theory is definitely real. Roughly speaking, each AdS solution is dual to the low energy physics of a different "material".

We know such material landscapes exist in condensed matter physics. Moreover, the mother theory (our "M-theory" if you like) is quite simple: electrons and nuclei interacting via electromagnetism. One can object that nuclei are not that simple, but we can always invoke the standard model up to a few hundred GeV to describe nuclei.

It seems then not hard to believe that the theory describing our universe has multiple solutions among which there is one in which we happen to find ourselves?

Another example:

Much discussion centers around whether the standard model is really well-defined or not at all energies (see e.g. Woit's blog comments), including talk of Landau poles and non-unitarity scattering, etc.

However, there is an even more basic issue. The standard model has not even really been defined at all, if by defined you mean "able to be put on a computer" (this is Wilson's definition). The standard model definitely cannot be a final theory because, as formulated, it is not even a complete theory.

And this doesn't mean naturalness is necessarily the right way to think, but something has to give. I suspect there is physics in the remarkable difficulty one encounters formulating a regulated theory which has things like Lorentz invariance and chiral gauge interactions (as an example of my thesis, I saw the issue of non-pert chiral gauge mentioned just once on the blog comments). Such a regulator may exist apart from fine-tuning, but I don't think anyone knows it.
 
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  • #7
phyzguy
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To me these arguments are akin to saying, "Newtonian gravity is unnatural, because, out of all of the infinity of values G could have, only one describes our universe." Huh?? Of course any physical theory will have undetermined parameters that need to be determined from observation - so what's new? Or am I missing something?
 

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