
Scale-invariant instantons and the complete lifetime of the standard model - vixen99
https://journals.aps.org/prd/abstract/10.1103/PhysRevD.97.056006
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morelandjs
...subject to our assumed framework and chosen prior. People always forget
that Bayes theorem only marginalizes over the unknown parameters. It assumes
the model is otherwise given (true). You can only marginalize over the known-
unknowns, not the unknown-unknowns.

People like to slip assumptions into their models where the uncertainties are
not accounted for. The reason why everyone trusts the LIGO result is that we
have an extremely high degree of confidence in general relativity.

More generally, what's even the point of placing a confidence level on a non-
falsifiable claim? What utility does it serve?

~~~
lisper
> The reason why everyone trusts the LIGO result is that we have an extremely
> high degree of confidence in general relativity.

No, that's not true. The reason everyone "trusts" the LIGO results is because
we believe the people running the experiment are trustworthy. The results have
nothing to do with GR except insofar as they were designed to test a
heretofore untested prediction of GR (which prediction they have confirmed).

And the reason we want to test a prediction of GR is that we want to try to
falsify it, because that is the way progress is made in science.

I think you may have meant to say something about how we cannot know for
certain that GR is true, that that's right, we can't. But it's not like
Einstein just pulled GR out of a hat. It's the only known solution to the
problem that fits all of the known data. That doesn't prove it's true, but it
is the best explanation we have so we might as well carry on as if it's true
until someone proves otherwise or comes up with a better idea.

~~~
AnimalMuppet
I don't think that LIGO was designed (only) to test GR. It was also set up to
be an astronomical observatory. (I don't know which goal was considered more
important...)

~~~
lisper
Why do you think those are different goals?

~~~
AnimalMuppet
Because in the astronomy part, we're _assuming_ the GR is correct, and using
it to watch astronomical events in a way we couldn't before.

For example, the detected neutron star merger tested that gravitational waves
travel at the speed of light, since we were able to also detect the fast gamma
ray burst from it. That's testing GR. But it also showed that such fast gamma
ray bursts come from the merger of two neutron stars. That's not testing GR.

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empath75
> Furthermore, since the lifetime is finite and the Universe infinite, there
> is likely a bubble of true vacuum already out there, far away. It is
> sobering to envision this bubble, with its wall of negative energy,
> barreling towards us at the speed of light. It seems the long-term future of
> our Universe is not going to be slow freezing due to cosmic acceleration but
> an abrupt collision with one of these bubble walls.

It seems like the more interesting calculation is how far away one of these
bubbles is likely to be.

~~~
jerf
I think the most solid argument in favor of the quantum multiverse is along
the lines of "The universe is virtually certain to fall into a lower-energy
quantum vacuum state. That we have not observed it to be the case means either
that we have been astonishingly lucky, or that there is a selection process
going on. There is such a selection process; we can only witness futures in
which the entire past lightcone of the universe has not collapsed; despite the
near-certainty that such has occurred there are still far more possible
universes than that." In short, the quantum multiverse argument can be run
backwards in time, too; a given quantum system will observe a superposition of
all possible past states of the universe as it evolves forward in time, and we
can only see the ones in which we still survive.

Now, I still don't believe in the quantum multiverse. We have not proved to my
satisfaction that lower-energy quantum vacuum states are inevitable, on the
grounds that we don't know enough yet to know why it hasn't happened. (i.e.,
there may be other effects keeping it from happening, or perhaps there are
reasons why it actually can't happen such as the lower state being non-viable
for some other reason, etc.) But in my opinion, this is still the most solid
argument in its favor; if it can be established that our current universe with
near-certainty should evolve into something that we can't live in or observe
with a bubble expanding at the speed of light, it's going to take something
equally potent to counteract that.

Or, in other words, under this theory, for every split second of your entire
life, vastly, vastly more of your worldlines are getting lightspeed-
annihilated than not. %99.999... "keep writing 9s as long as you like" of
them. But the destruction is so total and instantaneous that you can never
observe this fact, so you go on happily living in the 0.00...01% of the
remainder, happy as a clam. Again, this isn't my own personal belief, but it's
a theory.

~~~
T-A
> The universe is virtually certain to fall into a lower-energy quantum vacuum
> state. That we have not observed it to be the case means either that we have
> been astonishingly lucky, or that there is a selection process going on.

If that is the most solid argument in favor of the quantum multiverse, this
paper is a disaster. See Eq. 6.28: the probability that we should have seen a
bubble by now is < 10^-516.

~~~
jerf
When I quoted that argument, I was not saying it was 100% accurate; after all,
I don't believe it myself. If further work comes along to prove that the
collapse into the lower state is not highly probable, then the argument
collapses. Again, not accepting the multiverse anyhow, that the best argument
in its favor collapses would not particularly bother me.

Of course, it would not constitute evidence _against_ , merely a lack of
evidence _for_. Now, some people with a insufficiently deep understanding of
probabilities and such will say those two things are completely different, but
they aren't; lack of evidence for is indeed a form of evidence against,
especially if one is actively searching for the evidence. It just isn't very
strong, and it certainly isn't a proof.

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xchip
Physicist here: I hardly understand this paper so don't worry if neither do
you.

~~~
pw6hv
I don't understand what is the point of your comment, I am a physicist and I
understand this paper but this does not mean that others should worry if they
don't.

~~~
andrewmcwatters
I think it's public commentary on the ease of consumption of these papers on
HN on a wider scale than just physicists.

~~~
fwdpropaganda
In your opinion, what does it say about HN that people have the need to say
"this is very complicated, don't worry if you don't get it"?

~~~
AnimalMuppet
It says that people here _expect_ to be able to understand things. "I'm not
smart enough to understand physics" is not a normal self-image on HN.

~~~
fwdpropaganda
Bingo.

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PaulHoule
Talk about fine-tuning! How is it we are in the metastable area?

~~~
Coding_Cat
The anthropic principle, had we been in an unstable region, we wouldn't be
able to talk about it now.

A completely stable universe might also have some issues that are not
immediately clear.

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IIAOPSW
If their wrong no one can call them out on it.

~~~
empath75
Well, since it’s the result of a long chain of logic based on the standard
model and measurement of various constants, they could be proven wrong in a
variety of ways—their logic could be faulty, their calculations incorrect, or
the standard model itself could be flawed.

~~~
muhbags
The standard model is definitely flawed in a couple of known ways.

~~~
pw6hv
Correct, but modifications to the SM that can accommodate dark matter,
inflation or other phenomena not explained within the SM do not necessarily
change the picture of the SM vacuum instability.

