Can there ever be a Theory of Everything?

[bhobba]

I take it that you think there will be a "ToE" and we'll know when we find it?

Yes. And my gut tells me it will be some startling unexpected symmetry - but that is just my gut - which means diddley squat.

Thanks
Bill

 

[atyy]

I agree with the first sentence. From the second sentence, I take it that you think there will be a "ToE" and we'll know when we find it?

The reason I think the discussion has nothing to do with quantum theory is that the discussion is about how we can know any theory is a TOE. The answer is we cannot. We could have the TOE in principle, but we could not know that it can never be falsified, since we cannot test all its predictions. That is standard scientific faith which you can find in a biology textbook.

The more interesting thing is - can we know that a theory is not a TOE, even though it passes all experimental tests to date? Quantum mechanics gives us two examples.

1) The measurement problem

2) The renormalizability problem in QFT

Some would say that classical GR is an example of a theory that passes all experimental tests, and cannot be a TOE because of its singularties (this issue is debatable, but I include it here since the argument is reasonable).

However, it is really the measurement problem that is present in quantum theory in a way that is not present in classical theory. The renormalizability problem doesn't seem to me especially quantum, just a version of the singularity problem in classical GR. Here are two good expositions of the measurement problem:

http://www.tau.ac.il/~quantum/Vaidman/IQM/BellAM.pdf
Bell, Against 'measurement'

http://cds.cern.ch/record/260158/files/P00021853.pdf?version=1
Tsirelson, This non-axiomatizable quantum theory

Of course, if one takes a Bohmian or GRW or Transactional Interpretation viewpoint, then even the measurement problem can be classed with the renormalizability problem of QFT and the singularity problem of GR - these occur because the theories are incomplete - we know the theories are only effective theories, although they have not been falsified. However, QM has options that cannot be ruled out yet. For example, there is the Many-Worlds approach, in which we have objective reality, but it is radically different from our commonsense reality.

 

[audire]

I'm not sure if it's just me but this time of circular logic or "going around in circles" is something that people of all scientific fields can relate to. Just like you can have two independent observers reach the same conclusion under differing circumstances you can have 2+(multiple) observers arguing the same point and getting NOWHERE :P

 

[audire]

I'm not sure if it's just me but this time of circular logic or "going around in circles" is something that people of all scientific fields can relate to, and dread. Just like you can have two independent observers reach the same conclusion under differing circumstances you can have 2+(multiple) observers arguing the same point and getting NOWHERE :P

 

[Gort]

Getting back to true quantum theory and Gell-Mann, please see, for example, http://arxiv.org/pdf/1106.0767v3.pdf and http://arxiv.org/pdf/gr-qc/9912076.pdf. These articles talk about discrete (non-continuous) time in QM histories. When asked about whether this concept "could be real" at Scranton (see Bill's video), Gell-Mann said "time MAY be non-continuous, but that's NOT WHAT WE DO..."

So does this mean Gell-Mann believes it is not the place of physics to determine what is real? Only what "works"?

 

[atyy]

Getting back to true quantum theory and Gell-Mann, please see, for example, http://arxiv.org/pdf/1106.0767v3.pdf and http://arxiv.org/pdf/gr-qc/9912076.pdf. These articles talk about discrete (non-continuous) time in QM histories. When asked about whether this concept "could be real" at Scranton (see Bill's video), Gell-Mann said "time MAY be non-continuous, but that's NOT WHAT WE DO..."

So does this mean Gell-Mann believes it is not the place of physics to determine what is real? Only what "works"?

In the sense you are asking, yes, it is not the place of science to determine what is real. But that is only because you use a perverse definition of real.

According to you, cars are not real and people are not real. Apparently, you only consider atoms, quarks, strings or whatever undiscovered degrees of freedom exist to be real. This is in contrast to the attitude taken throughout physics, and even in quantum mechanics, where what is presumably an emergent property - the definite macroscopic outcome - is real, even though one doesn't know whether the wave function is real.

Because you use such a perverse definition of real, you cannot see the real weirdness of quantum mechanics.

 

[Gort]

In the sense you are asking, yes, it is not the place of science to determine what is real. But that is only because you use a perverse definition of real.

According to you, cars are not real and people are not real. Apparently, you only consider atoms, quarks, strings or whatever undiscovered degrees of freedom exist to be real. This is in contrast to the attitude taken throughout physics, and even in quantum mechanics, where what is presumably an emergent property - the definite macroscopic outcome - is real, even though one doesn't know whether the wave function is real.

Because you use such a perverse definition of real, you cannot see the real weirdness of quantum mechanics.

I'm not sure you understood the thread. I've quoted a published article, Hawking, and Gell-Mann. Then I asked a few questions. The only time I inserted my "view" was when I said I agreed with Hawking and I agreed the universe has laws and they're written in the language of mathematics. Don't think I've said what "I think" is real or not. Not sure where you got that from!

 

[atyy]

I'm not sure you understood the thread. I've quoted a published article, Hawking, and Gell-Mann. Then I asked a few questions. The only time I inserted my "view" was when I said I agreed with Hawking and I agreed the universe has laws and they're written in the language of mathematics. Don't think I've said what "I think" is real or not. Not sure where you got that from!

But you ask questions in which the word "real" is used. If you don't know what the word means, your question is meaningless.

 

[atyy]

I'm not sure you understood the thread. I've quoted a published article, Hawking, and Gell-Mann. Then I asked a few questions. The only time I inserted my "view" was when I said I agreed with Hawking and I agreed the universe has laws and they're written in the language of mathematics. Don't think I've said what "I think" is real or not. Not sure where you got that from!

OK, I've read the article by Hawking and Mlodinow. At first I thought the confusions were in the physics buzz blog you linked to, rather than in Hawking and Mlodinow's work. However, the references to The Matrix, the fish bowl and quantum particles not having definite positions are all from Hawking and Mlodinow's essay. So they are basically confused.

The fish bowl is the standard analogy - it has nothing to do with The Matrix. It is the same analogy as your cloud-covered planet analogy.

The Matrix is more like the brain in a vat problem. This is usually rejected by science as a matter of faith.

The lack of reality trajectories for quantum particles is something different from both. In the standard quantum interpretation, one rejects that we are in a Matrix, and there is commonsense reality, which might be like the fish bowl. The unusual thing about quantum mechanics is that we don't know, in the standard interpretation, whether the wave function belongs to the same level of reality as the fish bowl. So quantum mechanics, unlike classical physics and the fish bowl, has within the interpretation of the theory itself, a layer of non-reality (or at least reality-agnosticism) that is not present in classical theories. This extra layer is called the Heisenberg cut, and is a peculiarly quantum problem.

 

[Gort]

OK, I've read the article by Hawking and Mlodinow...etc.

Now, that's valid criticism. Not sure who agrees with it (that's what a Forum's for), but at least it's valid.

I was going to say that the terms "real" and "reality" were introduced by Hawking (not me). That's why I asked the questions in the first place. The only times I used the terms were in referencing Hawking, or in referencing Gell-Mann's talk, where he was asked about whether this concept [discreet time] "could be real".

Of course the terms "real" and "reality" are controversial, especially in a QM Physics Forum. But, since they were said by no less physicists than Hawking and Gell-Mann, I think the terms and all their connotations are fodder for discussion.

If I was wrong, I guess the thread quickly dies.

 

[atyy]

Of course the terms "real" and "reality" are controversial, especially in a QM Physics Forum. But, since they were said by no less physicists than Hawking and Gell-Mann, I think the terms and all their connotations are fodder for discussion.

But they are not. There are several different and valid definitions of these terms. What one should not do is confuse the definitions and switch from one definition to the next without realizing it. Even in classical physics, we do acknowledge that there are levels of realism with Newtonian mechanics, special relativity and general relativity being different levels of approximation, or "realism" if one wishes. There is nothing peculiarly quantum here.

What is peculiarly quantum is that the standard interpretation of quantum mechanics contains in itself two levels of reality - this is the Heisenberg cut.

One way to see the difference is that Newtonian mechanics does not itself tell us that it is incomplete. We know that because observations tell us that Newtonian mechanics is wrong.

At present, no observations tell us that quantum mechanics is wrong. But could the two levels of reality in quantum mechanics itself be telling us that quantum mechanics is incomplete, even though no observations falsify the theory?

 

[kith]

One way to see the difference is that Newtonian mechanics does not itself tell us that it is incomplete. We know that because observations tell us that Newtonian mechanics is wrong.

At present, no observations tell us that quantum mechanics is wrong. But could the two levels of reality in quantum mechanics itself be telling us that quantum mechanics is incomplete, even though no observations falsify the theory?

This reminds me of something I read in the introduction of Zee's book on general relativity today. Even without experimental evidence for the shortcomings of classical mechanics, one could have guessed that there was something missing. Without Planck's constant, the unit system necessarily depends on at least one arbitrary man-made unit. So motivated by the thought that the physics should fundamentally be independent of such concepts, one could have conjectured that classical mechanics is incomplete.

It would be intriguing if the measurement problem indicated something like this. However, my gut feeling tells me that more fundamental theories will be "incomplete" in the same way and that the alleged "incompleteness" of QM may be related to demanding unreasonable things from a physical theory.

 

[bhobba]

So does this mean Gell-Mann believes it is not the place of physics to determine what is real? Only what "works"?

No. It means if a hypothesis doesn't have testable predictions then any preference one way or another tells us more about the psychology of that choice than science. Again this subjective view of science, while appealing to philosophers of a certain type, is NOT science - it's promulgated by those that for some reason have given up on what science is about. Science is a search for objective TRUTH.

See what Weinberg says:
http://www.phys.washington.edu/users/vladi/phys216/Weinberg_Against_philosophy.doc

Regarding continuous time what Gell-Mann was talking about is the concept of history in his interpretation of QM - called Consistent Histories:
http://quantum.phys.cmu.edu/CHS/histories.html

A history, from its definition, is naturally discreet (its defined as a sequence of projection operators). There is no observation in that interpretation - QM is simply the stochastic theory about histories. Time is still continuous, as it is in QFT.

Thanks
Bill

 

[bhobba]

Even without experimental evidence for the shortcomings of classical mechanics, one could have guessed that there was something missing.

Exactly - Classical physics has a number of issues eg black-body radiation. Experiment, in general, keeps us honest; in and of itself its not what determines scientific progress. IMHO that's determined by asking the right questions, which is the view of the following:
https://www.amazon.com/dp/0521634202/?tag=pfamazon01-20

It really is the hardest thing to do - but its crucial to making progress as the above shows. Once they were asked progress was swift.

Its also gives a though rebuttal of the subjectivist view of science by Kuhn and others.

Thanks
Bill

 

[atyy]

This reminds me of something I read in the introduction of Zee's book on general relativity today. Even without experimental evidence for the shortcomings of classical mechanics, one could have guessed that there was something missing. Without Planck's constant, the unit system necessarily depends on at least one arbitrary man-made unit. So motivated by the thought that the physics should fundamentally be independent of such concepts, one could have conjectured that classical mechanics is incomplete.

I haven't read Zee's GR book, but thanks for that pointer! The lecturer in my first quantum mechanics class started with this argument, but I haven't seen it in many textbooks. Actually, I was thinking of another Zee book - the one on QFT - and his explanation of Wilsonian renormalization and gravity as a non-renormalizable theory indicating its status as an effective theory.

It would be intriguing if the measurement problem indicated something like this. However, my gut feeling tells me that more fundamental theories will be "incomplete" in the same way and that the alleged "incompleteness" of QM may be related to demanding unreasonable things from a physical theory.

I don't think the two ideas are opposed. It could be that the cut indicates an incompleteness, and it could also be that the theory that replaces QM will also have a cut. The alternatives to considering QM incomplete are not that the next theory will not have a cut. The alternatives are MWI or some rejection of commonsense reality.

To my mind, considering QM incomplete explains why Copenhagen is so wonderful, because it is a great effective theory, whereas any hidden variable theory will be much more complicated because of things like Hardy's excess baggage theorem or Montina's http://arxiv.org/abs/0711.4770v2.

 

[Andre Kosmos]

I would of posted the recent success of the BICEP2 experiment with evidence of gravity being quantized with the potential for a quantum gravity theory in under a decade to unify QM and QFT with GR & SR to eventually produce a ToE far superior in terms of the number of problems in our current candidate theories like string theory and loop quantum. Now its more like a century or two away.

All I can really say is to have hope for this to change as future data from cosmological observations and particle physics experiments becomes available.

 

[bhobba]

I would of posted the recent success of the BICEP2 experiment with evidence of gravity being quantized with the potential for a quantum gravity theory in under a decade to unify QM and QFT with GR & SR to eventually produce a ToE far superior in terms of the number of problems in our current candidate theories like string theory and loop quantum. Now its more like a century or two away.

We already have an effective quantum theory of gravity:
http://arxiv.org/abs/1209.3511

I checked that experiment:
http://physicsworld.com/cws/article...sult-bites-the-dust-thanks-to-new-planck-data

Cant find anything there that either invalidates our current theories or probes regions beyond its cutoff, which is about the Plank scale.

Thanks
Bill

 

[kith]

I haven't read Zee's GR book, but thanks for that pointer! The lecturer in my first quantum mechanics class started with this argument, but I haven't seen it in many textbooks. Actually, I was thinking of another Zee book - the one on QFT - and his explanation of Wilsonian renormalization and gravity as a non-renormalizable theory indicating its status as an effective theory.

Yes, this might be a similar issue. But to me, it seems to be on a different level than the measurement problem. Are there attemps to relate these two?

I'd like to read both of Zee's books in detail but I probably won't find the time. I really like how he uses intuitive reasoning a lot and how he acknowledges that some concepts may make people feel uneasy.

 

[kith]

I don't think the two ideas are opposed. It could be that the cut indicates an incompleteness, and it could also be that the theory that replaces QM will also have a cut. The alternatives to considering QM incomplete are not that the next theory will not have a cut. The alternatives are MWI or some rejection of commonsense reality.

True but the latter could be a fundamental principle of science. On the one hand, we have the naive realism of everyday life and on the other hand, we have the knowledge we acquire by the scientific method. That both are on the same footing is not a small assumption. It seemed straightforward in classical physics but throughout the centuries, there were always people who felt uneasy about things like this.

Let's take the simple example of a simultaneous position and velocity. In everyday life, velocity is how fast something moves between two points. That you can define a velocity at a single point is marvelous mathematics but if a contemporary of Newton insisted that it this isn't something real but a tool we use, he would have been quite in line with a more modern Copenhagen-like world view.

To my mind, considering QM incomplete explains why Copenhagen is so wonderful, because it is a great effective theory, whereas any hidden variable theory will be much more complicated because of things like Hardy's excess baggage theorem or Montina's http://arxiv.org/abs/0711.4770v2.

I think Bohr wouldn't agree with your terminology of incompleteness because these complicated things cannot be observed. But we all agree that it's wonderful. ;-) From the perspective of incompleteness, I really admire Bohr's atomic model. It must have looked so odd and wrong to many people but it really fleshed out the important features of quantum theory at the time and made Heisenberg's breakthrough possible.

 

[lucas_]

Yes. And my gut tells me it will be some startling unexpected symmetry - but that is just my gut - which means diddley squat.

Thanks
Bill

What are the mathematical clues to this startling unexpected symmetry? maybe something that will interchange spacetime and matter? didn't we have any symmetry that can enclose them? were you talking about U(1)xSU(2)xSU(3) kind of symmetry like SU(5) or the GR symmetry? Remember Einstein tried to unite GR and matter by treating all of them as geometry or matter as geometry. If you feel you are not comfortable in this quantum forum, you can reply in the thread about this at Beyond the Standard Model https://www.physicsforums.com/threads/emergent-spacetime-matter.803466/

 

[bhobba]

What are the mathematical clues to this startling unexpected symmetry?

Beats me.

If I knew I would be earning my Nobel prize.

Its unlikely to be anything like what happened before - super-symmetry, which is its logical conclusion seems a dead end.

Its simply a belief that the self similarity as we peel away the onion rings will continue as per what Murray Gell-Mann said.

Thanks
Bill

 

[lucas_]

Beats me.

If I knew I would be earning my Nobel prize.

Its unlikely to be anything like what happened before - super-symmetry, which is its logical conclusion seems a dead end.

Its simply a belief that the self similarity as we peel away the onion rings will continue as per what Murray Gell-Mann said.

Thanks
Bill

How many years I have to study before I can have your mathematical knowledge and atyy knowledge too? I have spent 10 yrs reading over 100 laymen books on physics. I'm already 45 yrs old. I can't go back to college again. If only physicists would do their job. We could have spent our time elsewhere instead of spending so many hours a day studying it from scratch. But mainstream physicists are just so close minded. They only focused on what they expected to see. Not knowing that the very clues they ignored are keys to the full unification and and answer to that radical unexpected symmetry you talked about. But since the clues are banned in this forums.. and mainstream physicists ignored it.. then it is left to us who have witnessed them to pave the way. If we failed, then physics have to wait for a hundred years more for the real final theory because physicists are doing it blind, they will improve by leap and bounds if they have the clue ("the clue sprung from the soil of observational physics, and therein lies their strength. They are radical..." Minkowski words will be repeated soon again).

 

[Delta2]

We have at least two theories of everything namely string theory and quantum loop gravity but the problem with these two theories is that they are not experimentally tested or verified for any result that may predict within the framework of the http://en.wikipedia.org/wiki/Scientific_method at least not with current day's technology. So we can't say if they are true or false because the scientific method cannot be applied for them. In these days we are living String theory QLG,Quantum Physics and GR are just theories. It is the scientific method that is our one and only method with which we decide which theories are true , which are false and which are partially true. I think the physics needs to go one step beyond and find other methods with which to test the validity of any theory.

 

[bhobba]

How many years I have to study before I can have your mathematical knowledge and atyy knowledge too?

Don't worry - there is still plenty of time to go into the detail.

Start with this:
https://www.amazon.com/dp/0471827223/?tag=pfamazon01-20
https://www.amazon.com/dp/0465075681/?tag=pfamazon01-20
https://www.amazon.com/dp/0465036678/?tag=pfamazon01-20

There are associated video lectures for the last two:
http://theoreticalminimum.com/courses/classical-mechanics/2011/fall
http://theoreticalminimum.com/courses/quantum-mechanics/2012/winter

Work your way through it, take your time and post with any questions.

Once you have done that get back and we can chat about your next steps.

Regarding the other stuff we will see how you feel once you have learn't the detail. Remember guys like Einstein that made the big breakthroughs were very well versed in the current theories of their time. That's really the only way to see the issues they have.

Thanks
Bill

 

[DevilsAvocado]

I think this is what Hawking has realized (again, this is Hawking - not me!). He decided that there may be no such thing as a ToE because we don't know (and probably will never know) exactly how Nature works.

Maybe the blog has confused you, I recommend reading the book instead, which gives a much clearer view on what Hawking is talking about. When it comes to "reality" he is basically referring to the implications QM put on what could be considered real (i.e. existing/there all the time), and when it comes to the Theory of Everything he is naturally referring to a unified quantum theory, including all the four fundamental forces. A theory of everything does not mean that we would know absolutely everything about everything... although a unified quantum theory will give us a lot of 'power' in that direction.

"But the division of natural forces into four classes is probably artificial and a consequence of our lack of understanding. People have therefore sought a theory of everything that will unify the four classes into a single law that is compatible with quantum theory. This would be the holy grail of physics."

Newtonian gravity matched observations. So it became entrenched in a ToE. But was it actually a ToE? No - suppose we suddenly invent rockets and the universe is opened up to us. Suddenly, we need a new "ToE".

Newtonian gravity can never be wrong, it will always work the same way – within its domain. This is how science works. When a new theory comes along, it expands the domain and deepens our understanding, whilst at the same time it includes previous knowledge and verified facts in the new framework.

"Can theories built upon a framework so foreign to everyday experience that were modeled so accurately by classical physics? They can, for we and our surroundings are composite structures, made of an unimaginably large number of atoms, more atoms than there are stars in the observable universe. And though the component atoms obey the principles of quantum physics, one can show that the large assemblages that form soccer balls, turnips, and jumbo jets - and us - will indeed manage to avoid diffracting through slits. So though the components of everyday objects obey quantum physics, Newton's laws form an effective theory that describes very accurately how the composite structures that form our everyday world behave."

 

[Gort]

Newtonian gravity can never be wrong, it will always work the same way – within its domain. This is how science works. When a new theory comes along, it expands the domain and deepens our understanding, whilst at the same time it includes previous knowledge and verified facts in the new framework.

Nobody said Newtonian gravity could be wrong. It's a very good Theory of Something (ToS). There's lots of good ToS's. Theories that are valid within certain constraints, initial conditions, geometries, etc. But its not a ToE. It doesn't claim to be.

...when it comes to the Theory of Everything he is naturally referring to a unified quantum theory, including all the four fundamental forces. A theory of everything does not mean that we would know absolutely everything about everything... although a unified quantum theory will give us a lot of 'power' in that direction.

Of course a ToE doesn't mean we'll know "absolutely everything about everything", but it DOES imply that about the physical world. That's what a ToE is. By definition. And somehow, we'll have to test that it applies to "absolutely everything about everything". That's the question - can we make that test and how will we know when we get a positive result?

 

[bhobba]

That's what a ToE is. By definition.

That's not what a TOE is. In a sense we already have a TOE in that it agrees with all known experimental results. It however is aesthetically ugly. We want something without that ugliness eg the large number of parameters that needs to be put in by hand. As one theorist expressed it the standard model has parts of dazzling beauty and other parts that are a kluge - we want to get rid of the kludge.

Thanks
Bill

 

[rootone]

I think that there will always be a theory of almost, but not quite, everything.
There will always be something that we don't quite get, but we carry on striving to get to it.
That has to be a good thing, well definitely is not a bad thing.

 

[Gort]

In a sense we already have a TOE in that it agrees with all known experimental results. It however is aesthetically ugly.

Please explain what "it" is. I suppose we can define ToE any way you'd like, including a sum of "Theories of Somethings" or ToS's. In that sense, we do have lots of ToS's. The fact that we have to put ToS's together (stitched like a quilt) is "ugly", I suppose. But I subscribe to the idea that a ToE is a SINGLE theory or framework. As an example of an attempt, David Deutsch (a quantum physicist at the University of Oxford) tried to develop a framework that could encompass all physical theories by determining a set of overarching “meta-laws” that describe what can happen in the universe and what is forbidden. See http://arxiv.org/ftp/arxiv/papers/1405/1405.5563.pdf.

 

[bhobba]

Please explain what "it" is..

I thought it was rather obvious.

The standard model and an effective field theory of gravity.

It has a number of ugly issues eg the already alluded to large number parameters and the Landau pole in the Electroweak theory.

I personally don't know what a TOE will look like except it won't be ugly - it will all be the dazzling beauty some parts of the SM have.

Thanks
Bill