Is the multiverse fake physics?

  • I
  • Thread starter kodama
  • Start date
  • Featured
  • #1
725
84

Main Question or Discussion Point

woit over at his blog not even wrong considers string theory based multiverse to be fake physics. he cites sean carroll as others on his blog as examples of fake physics.

is string theory based multiverse fake physics?
 

Answers and Replies

  • #2
Orodruin
Staff Emeritus
Science Advisor
Homework Helper
Insights Author
Gold Member
16,817
6,624
It is customary to include a link when discussing blog posts or similar.
http://www.math.columbia.edu/~woit/wordpress/
Not everyone reading will know the blog.

I think he has a clear point. Large parts of theoretical physics has become untestable and therefore unscientific. Trying to sell this as facts or success is misleading.
 
  • Like
Likes Dr. Courtney and OCR
  • #3
ohwilleke
Gold Member
1,498
398
I agree that the multiverse (not to be confused with the many worlds interpretation of QM) is fake physics.
 
  • Like
Likes Dr. Courtney
  • #4
Orodruin
Staff Emeritus
Science Advisor
Homework Helper
Insights Author
Gold Member
16,817
6,624
I agree that the multiverse (not to be confused with the many worlds interpretation of QM) is fake physics.
To be honest, I would still place QM interpretations into the same category. It is also a subject that is given far too much attention in popular discussion on QM.
 
  • Like
Likes Student100, beamie564, Fervent Freyja and 1 other person
  • #5
haushofer
Science Advisor
Insights Author
2,302
673
I agree that the multiverse (not to be confused with the many worlds interpretation of QM) is fake physics.
Can you elaborate?
 
  • #6
725
84
Can you elaborate?
ohwilleke is replying to my thread which is itself based on the claims of peter woit on not even wrong that
the multiverse is fake physics in analogy to fake news. even when claims of multiverse comes from
a cosmologist and phd like sean carroll or brian greene it is still fake physics.

woit says claims of the multiverse is based on string theory unification, which he regards to be a failed
research program, therefore physicists like sean carroll and several others he mentions are not discussing
genuine physics to a lay public.

what do the resident string theorists here say to this claim, i.e urs shcrieber et al
 
  • #7
haushofer
Science Advisor
Insights Author
2,302
673
ohwilleke is replying to my thread which is itself based on the claims of peter woit on not even wrong that
the multiverse is fake physics in analogy to fake news. even when claims of multiverse comes from
a cosmologist and phd like sean carroll or brian greene it is still fake physics.

woit says claims of the multiverse is based on string theory unification, which he regards to be a failed
research program, therefore physicists like sean carroll and several others he mentions are not discussing
genuine physics to a lay public.

what do the resident string theorists here say to this claim, i.e urs shcrieber et al
Well, I've read a fair amount of string theory and my own research involved it, so let me give my 2 cents.

The motivation for the multiverse from string theory is shaky. It involves an interpretation of the landscape, which is on its own quite ad hoc. I think the motivation from inflation is stronger: to get the right amount of inflation results quite naturally in eternal inflation. Let's say that at some time in the future we are very confident that inflation happened, and that our model implies eternal inflation. Philosophically, we entered then a boundary of our understanding: we have no way to falsify the implied multiverse, but as a consequence of our model we should take it seriously. There is nothing fake about that. It would be fake to reject it because we don't like the idea that we bumped into an end of our understanding. Physics thaught us that we should take our equations seriously. If we are just one bubble in a multiverse and we cannot enter those other bubbles, then that's the way reality is; nature doesn't care about being falsifiable.

But often people combine this 'inflationary multiverse' with the 'string landscape multiverse'. I don't see how that happens, and it is far from clear what the relation (if any) is. Let alone the multiverse from the MWI-interpretation. It is only in those cases you enter these "theory of anything"-objections agains the multiverse.

To be honest, if I had to choose, I would say that the MWI-interpretation of the multiverse is much more shaky than the inflationary multiverse. I've never understood why people like MWI, but that could also be my lack of deep knowledge of it.
 
  • Like
Likes amyami, nnunn, Andrew Bridges and 6 others
  • #8
haushofer
Science Advisor
Insights Author
2,302
673
To be honest, I would still place QM interpretations into the same category. It is also a subject that is given far too much attention in popular discussion on QM.
It depends on how you view science and physics. I strongly disagree with your view. Ontology, and as such interpretational issues, should imo be considered as a part of physics, and not 'just' philosophy.
 
  • Like
Likes amyami
  • #9
Orodruin
Staff Emeritus
Science Advisor
Homework Helper
Insights Author
Gold Member
16,817
6,624
It depends on how you view science and physics. I strongly disagree with your view. Ontology, and as such interpretational issues, should imo be considered as a part of physics, and not 'just' philosophy.
As you have guessed, I strongly disagree with this. If there are no testable differences, I see no scientific point in debating the issue. Just pick whichever interpretation you fancy (if you must) and nobody can disagree with you. To me this violates the very core of empirical science.
 
  • Like
Likes Paul Colby, Andrew Bridges, Jamison Lahman and 4 others
  • #10
2,788
587
As you have guessed, I strongly disagree with this. If there are no testable differences, I see no scientific point in debating the issue. Just pick whichever interpretation you fancy (if you must) and nobody can disagree with you. To me this violates the very core of empirical science.
What if in 10 years, people still have no explanation for fine tuning? In 50 years? In 100? Even then you don't think we should consider the multiverse?
 
  • #11
Orodruin
Staff Emeritus
Science Advisor
Homework Helper
Insights Author
Gold Member
16,817
6,624
What if in 10 years, people still have no explanation for fine tuning? In 50 years? In 100? Even then you don't think we should consider the multiverse?
No. It is a concept similar to God (I am using God to cover three of the main world religions - anyone may substitute for personal preference). I give you the two hypotheses:
  1. Fine tuning exists because of the multiverse.
  2. Fine tuning exists because God wanted it so.
I ask you the question: What testable differences exist between those two hypotheses?
If neither hypothesis can be falsified, I simply chose the agnostic path and do not include any of the hypotheses in my scientific description of how the world works. (I also have the same approach to religion by the way, but that is a different matter.)
 
  • Like
Likes nnunn, Andrew Bridges, Jamison Lahman and 2 others
  • #12
2,788
587
No. It is a concept similar to God (I am using God to cover three of the main world religions - anyone may substitute for personal preference). I give you the two hypotheses:
  1. Fine tuning exists because of the multiverse.
  2. Fine tuning exists because God wanted it so.
I ask you the question: What testable differences exist between those two hypotheses?
If neither hypothesis can be falsified, I simply chose the agnostic path and do not include any of the hypotheses in my scientific description of how the world works. (I also have the same approach to religion by the way, but that is a different matter.)
The difference is that eternal inflation may be a good theory with strong observational support. We may find out that we can't come up with a better theory. Why should we throw out a prediction of our only good theory?
Its like gravitational waves, people didn't doubt their existence. No one actually was surprised when they were discovered because GR is a very well established theory.
 
  • #13
Orodruin
Staff Emeritus
Science Advisor
Homework Helper
Insights Author
Gold Member
16,817
6,624
The difference is that eternal inflation may be a good theory with strong observational support.
Please show me this observational support.

We may find out that we can't come up with a better theory. Why should we throw out a prediction of our only good theory?
What do you mean "better"? If two theories makes the exact same predictions apart from things that cannot be tested - they are the same theory for all practical purposes and you can never find out which is preferred. Predictions that cannot be tested are not predictions because predictions by definition makes statements about things that will occur or not.

Its like gravitational waves, people didn't doubt their existence. No one actually was surprised when they were discovered because GR is a very well established theory.
This is different. Gravitational waves were a priori testable and based on the current dominating theory - which had already made a large amount of verified predictions that differed from its predecessor (Newtonian gravity) - they should be there. So I ask you, what predictions of the multiverse have been observed that cannot be explained without it?
 
  • Like
Likes Dougias
  • #14
2,788
587
Please show me this observational support.
I said maybe. I meant in the future, it may turn out to be so!
What do you mean "better"? If two theories makes the exact same predictions apart from things that cannot be tested - they are the same theory for all practical purposes and you can never find out which is preferred. Predictions that cannot be tested are not predictions because predictions by definition makes statements about things that will occur or not.
In the future, hypothetically, just imagine, that eternal inflation explains all observations really well and any other theory that doesn't predict a multiverse, is much more complicated. Imagine its like the choice between SR and aether theories. So people choose eternal inflation. They have observed all its predictions except for the multiverse. Why should they assume its not true?
 
  • #15
Orodruin
Staff Emeritus
Science Advisor
Homework Helper
Insights Author
Gold Member
16,817
6,624
In the future, hypothetically, just imagine, that eternal inflation explains all observations really well and any other theory that doesn't predict a multiverse, is much more complicated. Imagine its like the choice between SR and aether theories.
But this is the other way around! You can do away with the aether in LET and just be left with SR because there is no need to assume the aether of LET. In the same way, there is no need to assume an eternal inflation to explain what is going on in the observable universe.

Of course you can try to extrapolate a theory, but doing so you must be aware of that this is what you are doing - just as we know that we are extrapolating GR to a domain that by definition of the theory itself is untestable when we try to describe the interior of a black hole. If the theory is true in that regime - then you can never know that it is.
 
  • #16
725
84
But this is the other way around! You can do away with the aether in LET and just be left with SR because there is no need to assume the aether of LET. In the same way, there is no need to assume an eternal inflation to explain what is going on in the observable universe.

Of course you can try to extrapolate a theory, but doing so you must be aware of that this is what you are doing - just as we know that we are extrapolating GR to a domain that by definition of the theory itself is untestable when we try to describe the interior of a black hole. If the theory is true in that regime - then you can never know that it is.
where does string theory and its prediction belong on this list?
 
  • #17
FactChecker
Science Advisor
Gold Member
5,581
2,059
As you have guessed, I strongly disagree with this. If there are no testable differences, I see no scientific point in debating the issue. Just pick whichever interpretation you fancy (if you must) and nobody can disagree with you. To me this violates the very core of empirical science.
Are you saying that something must be testable in order to be true? Or is your objection more about calling it physics?
What about a modern theory that is compatible with all we know today? Doesn't that imply that it passes the "test" of all our current knowledge?
 
  • #18
haushofer
Science Advisor
Insights Author
2,302
673
As you have guessed, I strongly disagree with this. If there are no testable differences, I see no scientific point in debating the issue. Just pick whichever interpretation you fancy (if you must) and nobody can disagree with you. To me this violates the very core of empirical science.
A physical theory must do more than just 'agree with observation' in view of future development. An example is given by the epicykle theory, which reproduces observations concerning our solar system perfectly in a geocentric model. Mathematically we now understand why: given any irregular shaped closed curve, we can always use a finite number of epicykels to explain such a curve.

That's why I don't understand how some people can just put ontology into the 'philosophy'-corner and pretend it is not part of physics. It is. E.g., one reason why quantum gravity is not well understood could be in a similar fashion as the epicykels: we can calculate with it, but by regarding QM just as a bookkeeping device, we could overlook crucial hints which are important when considering gravity.

Similary, nowaydays the discussion about the nature of spacetime and the meaning of coordinates can be regarded as 'mere philosophy', but it troubled Einstein so much that for two years he abandoned general covariance. And I think that general covariance is still not thoroughly understood, by the community and also by a lot of professional physicists.
 
  • Like
Likes Auto-Didact, nnunn and substitute materials
  • #19
Orodruin
Staff Emeritus
Science Advisor
Homework Helper
Insights Author
Gold Member
16,817
6,624
A physical theory must do more than just 'agree with observation' in view of future development.
Yes, it must do so without introducing additional arbitrary epicycles that can fit any observation. Furthermore, epicycles would have lost out to Occam's razor long ago.

we can calculate with it, but by regarding QM just as a bookkeeping device, we could overlook crucial hints which are important when considering gravity.
Introducing different equivalent interpretations is not going to help you achieve this. Thinking about different and a priori distinguishable theories just might.
 
  • #20
264
38
To be honest, if I had to choose, I would say that the MWI-interpretation of the multiverse is much more shaky than the inflationary multiverse. I've never understood why people like MWI, but that could also be my lack of deep knowledge of it.
There are good reasons to be concerned about the unitary-only MWI approach. If one looks deeply into the foundations of MWI, one finds circularity and arguably worse logical fallacies. See, e.g, https://arxiv.org/abs/1406.4126 and https://arxiv.org/abs/1603.04845
 
  • Like
Likes haushofer
  • #21
297
522
...the two hypotheses:
Fine tuning exists because of the multiverse.
Fine tuning exists because God wanted it so.
― but they both might very well be true together ― just imagine the Great Supernatural Computer simulating all the Multiverse, including all those quantum Many Worlds in the whole space-time, all at once, as the Potentiality. Then, what remains to happen, is the actual choices of the observed events, made by the supernatural players of the great computer game (the first move is the choice of the good fine tuned Nature). It's called the "process formulation":

"The process formulation of quantum theory contains no explicit dependence on human observers: it allows quantum theory to be regarded as a theory describing the actual unfolding or development of the universe itself, rather than merely a tool by which scientists can, under special conditions, form expectations about their observations. The quantum theory of process is in general in accord with the ideas of the physicist, logician, and process philosopher Alfred North Whitehead. In particular, the actual is represented not by an advancing, infinitely thin slice through the space-time continuum, but rather by a sequence of actual becomings, each of which refers to a bounded spacetime region: event number n is represented, within physical theory, by a restriction on the set of classical fields allowed in the bounded space time region R(n). We have, therefore, neither becoming in three-dimensional space nor being in the four-dimensional world, but rather becoming in the four-dimensional world. "

Henry Stapp, "Physics and the Ultimate Significance of Time", page 267.
 
  • #22
34,370
10,445
A finite number of epicycles cannot match the predictions of GR exactly - they cannot take the mutual attraction between planets into account, for example. You can always find a set large enough to be consistent with current observations, of course, but hundreds of epicycles clearly lose compared to GR.

Where is the relation to the idea of multiple universes? I'm not aware of any hypothesis that would introduce hundreds of arbitrary parameters tuned to some observations. The fundamental laws of the set of universes in those multiverse approaches are usually extremely simple. They do not necessarily make predictions about the fundamental constants of our universe - but we have many theories that do not make those predictions. The Standard Model is a well established theory, although it has free parameters it cannot predict, and its predictions are limited to particles we already know. How would a theory that implies multiple universes with different values for the free parameters of the SM be worse than that? It can predict the same as the SM, and it can be falsified in the same way (here: by finding violations of the SM). If it makes predictions beyond that, e.g. some structures in the CMB, neutrino or GW background: even better.
 
  • Like
Likes AaronK and kodama
  • #23
Large parts of theoretical physics has become untestable and therefore unscientific. Trying to sell this as facts or success is misleading.
In other areas, when the accepted methodology generates scenarios which appear incompatible with that methodology, it is the methodology which comes under scrutiny. Similarly, if the search for truth leads to scientifically untestable theories, this may indicate a problem with Science, rather than the search for truth.
 
  • #24
86
16
Earth used to be The planet, The Universe.
Is the multi planet a fake? The multi solar system? The multi galaxy?
If, somehow, some entity exist, why not exist twice? Many? Infinity? Why not multi universe?
I think multiverse make sense in many many ways.
 
  • #25
Orodruin
Staff Emeritus
Science Advisor
Homework Helper
Insights Author
Gold Member
16,817
6,624
Why not multi universe?
I think multiverse make sense in many many ways.
Because it is inherently untestable. It might exist but you have no way of knowing that it does. Other planets, stars, and galaxies were never untestable - it was just a matter of constructing a large enough telescope.
 
  • Like
Likes Auto-Didact

Related Threads on Is the multiverse fake physics?

Replies
4
Views
2K
  • Last Post
2
Replies
28
Views
8K
  • Last Post
Replies
1
Views
3K
Replies
5
Views
3K
  • Last Post
2
Replies
34
Views
6K
  • Last Post
Replies
7
Views
1K
  • Last Post
Replies
1
Views
971
  • Last Post
Replies
7
Views
9K
Replies
4
Views
4K
  • Last Post
Replies
14
Views
4K
Top