Understanding TOE & QG: A Comparison for Physicists

[pivoxa15]

Just want to get some terminology right. Is TOE equivalent to QG?

If so is QG more frequently used by physicsts as it sounds more professional or simply more logical?

 

[George Jones]

Is TOE equivalent to QG?

In my opinion, no.

A quantum theory of gravity might be just a quantum theory of gravity, and not a theory of everything.

A theory of everything, again in my opinion, would have to include a quantum theory of gravity.

Another, *highly* speculative idea is that a theory of everything would modify things so much that quantum theory itself would no longer be valid (in appropriate domains).

 

[staf9]

In theory, no;

But, in my opinion, it all depends on the extent to which QG explains all other phenomena in physics. We won't know the extent to which QG explains other phenomena until it's figured out.

 

[arivero]

The original meanings of GUT and TOE are discussed somewhere by John Ellis, the proponent of the second word. It seems it has evolved a little.

EDIT: can someone provide a quote from "Physics gets physical", of Ellis, in Nature?

 

[Haelfix]

Toe = matter (GUT) + QG. Where the coupling constants of matter converge to the coupling constants of gravity (General relativity) and they all unite in some way.

String theory is sort of a TOE, whereas traditional LQG is purely QG (no matter.. yet).

The idea is you want a sort of fundamental high energy theory that's relatively simple, and then mechanisms like spontaneous symmetry breaking decouples everything and leads to all the complicated interactions we see at our scales.

 

[pivoxa15]

Doesn't QFT or quantum theory describe matter (fundalmental particles)?

 

[pivoxa15]

In my opinion, no.

A quantum theory of gravity might be just a quantum theory of gravity, and not a theory of everything.

A theory of everything, again in my opinion, would have to include a quantum theory of gravity.

Another, *highly* speculative idea is that a theory of everything would modify things so much that quantum theory itself would no longer be valid (in appropriate domains).

Whats something that can't by explained by quantum theory nor GR?

 

[pivoxa15]

Toe = matter (GUT) + QG. Where the coupling constants of matter converge to the coupling constants of gravity (General relativity) and they all unite in some way.

String theory is sort of a TOE, whereas traditional LQG is purely QG (no matter.. yet).

The idea is you want a sort of fundamental high energy theory that's relatively simple, and then mechanisms like spontaneous symmetry breaking decouples everything and leads to all the complicated interactions we see at our scales.

Doesn't quantum theory describe all fundamental matter?

 

[marcus]

pivoxa in post #6 you asked Doesn't QFT or quantum theory describe matter (fundalmental particles)?

Try thinking of it this way:
quantum mechanics > QFT > SM which describes matter if you plug in some 20 or 30 numbers

quantum mechanic is a very general framework which doesn't describe anything in particular. It is a bunch of ideas, math formalism, principles, practices etc. which you can use to construct quantum theories most of which are wrong or simply meaningless. Most theories of any kind are wrong or meaningless, after all. But the quantum framework is excellent (we don't know yet, perhaps all good theories have to be constructed within it, or it might turn out not to be fundamental after all, nobody can predict the future).

within the excellent general framework of quantum mechanics one can construct a more specialized thing called QFT. this also does not describe anything in particular.
It comes in an infinite number of versions and you can devise versions of QFT which are nonsense.

However if you make certain choices you can set up a version of QFT called STANDARD MODEL, and the SM does describe observed particles of matter!

It might not describe everything exactly right. It might not explain Dark Matter. It might not explain why the cosmological constant is 0.6 joules per cubic kilometer. It might not predict Dark Energy correctly. It might not have much to say about 96 PERCENT OF THE UNIVERSE's stuff. But is does a really really impressive job accounting for the remaining 4 PERCENT!

And of course it doesn't account for spacetime geometry. It doesn't explain gravity----why and how matter interacts with geometry. But that is a separate issue.

So be happy. think about the picture
QM > QFT > SM

Quantum mechanics, the general quantum framework does NOT describe particles but you can use it to construct QFT.

QFT still doesn't tell you what nature looks like, because it comes in an infinite number of versions, but you can use it to construct SM

SM is pretty good, finally, but still has some problems.
(You have to fine tune 26 or so numbers that you have to plug in. it doesn't explain why those particular 26-odd numbers---we could use a whole new theory to explain them. And even with those 26 numbers adjusted, the SM still has issues. Does the proton eventually decay or not? Should SM be extended to include supersymmetric partners? Exactly how and why have they never been seen? At what energy scale do the electro and the weak part company, and how do they do that? At what scale do the electro and weak and strong all unify? And still nothing said about gravity.)

So SM is pretty good but it still has problems.

this is just my take on it. Maybe someone else would like to correct my overall perspective or some details of it. did you check Wikipedia about standard model?

pivoxa in post #7 you said Whats something that can't by explained by quantum theory nor GR?

I hope what I just posted gives some ideas----like for example Dark Energy, but actually a lot of other things too.
I think that post #7 was asking George Jones, sorry to jump in. I would like to see his response too.

 

[George Jones]

Whats something that can't by explained by quantum theory nor GR?

I don't know of anything empirical for which quantum theory and GR is not a possible explanation .

I just meant that no physical theory, including quantum theory, is sacred. History teaches us theories sometime fail. When mild tweaking brings the theory back into alignment with experiment, then the modified theory might not be considered new, and the theory might retain its name, but if a radical theoretical rewrite is required, then the resulting theory might be considered new, and might have a new name. For example, Newtonian theory ---> quantum theory. We might find data which shows that quantum theory is not universally valid, i.e., quantum theory ---> ?, where ? no longer uses the name "quantum".

As marcus says we might already have such data, but I think it's more likely that a quantum theory of gravity, whether or not its part of a TOE, will explain this data.

However, we can't rule out that our present data will lead us to a new theory that can no longer use the name 'quantum', and, even if this isn't so, we must always be open to the possibility that future data might require this.

This would be tremendously exciting!

 

[setAI]

nope- it would just be a single theory to describe the sum of all emergent causality of this type of world

any real TOE would IMO have to start from the "Monad" and describe how the phase space of universes is generated through it's self-interaction

 

[pivoxa15]

pivoxa in post #6 you asked Doesn't QFT or quantum theory describe matter (fundalmental particles)?

Try thinking of it this way:
quantum mechanics > QFT > SM which describes matter if you plug in some 20 or 30 numbers

quantum mechanic is a very general framework which doesn't describe anything in particular. It is a bunch of ideas, math formalism, principles, practices etc. which you can use to construct quantum theories most of which are wrong or simply meaningless. Most theories of any kind are wrong or meaningless, after all. But the quantum framework is excellent (we don't know yet, perhaps all good theories have to be constructed within it, or it might turn out not to be fundamental after all, nobody can predict the future).

within the excellent general framework of quantum mechanics one can construct a more specialized thing called QFT. this also does not describe anything in particular.
It comes in an infinite number of versions and you can devise versions of QFT which are nonsense.

However if you make certain choices you can set up a version of QFT called STANDARD MODEL, and the SM does describe observed particles of matter!

It might not describe everything exactly right. It might not explain Dark Matter. It might not explain why the cosmological constant is 0.6 joules per cubic kilometer. It might not predict Dark Energy correctly. It might not have much to say about 96 PERCENT OF THE UNIVERSE's stuff. But is does a really really impressive job accounting for the remaining 4 PERCENT!

And of course it doesn't account for spacetime geometry. It doesn't explain gravity----why and how matter interacts with geometry. But that is a separate issue.

So be happy. think about the picture
QM > QFT > SM

Quantum mechanics, the general quantum framework does NOT describe particles but you can use it to construct QFT.

QFT still doesn't tell you what nature looks like, because it comes in an infinite number of versions, but you can use it to construct SM

SM is pretty good, finally, but still has some problems.
(You have to fine tune 26 or so numbers that you have to plug in. it doesn't explain why those particular 26-odd numbers---we could use a whole new theory to explain them. And even with those 26 numbers adjusted, the SM still has issues. Does the proton eventually decay or not? Should SM be extended to include supersymmetric partners? Exactly how and why have they never been seen? At what energy scale do the electro and the weak part company, and how do they do that? At what scale do the electro and weak and strong all unify? And still nothing said about gravity.)

So SM is pretty good but it still has problems.

this is just my take on it. Maybe someone else would like to correct my overall perspective or some details of it. did you check Wikipedia about standard model?

pivoxa in post #7 you said Whats something that can't by explained by quantum theory nor GR?

I hope what I just posted gives some ideas----like for example Dark Energy, but actually a lot of other things too.
I think that post #7 was asking George Jones, sorry to jump in. I would like to see his response too.

SO QM has a similarity with string theory. We don't actaully know exactly what string theory is as we don't know what M theory is. So until M theory is fully worked out there is still hope that a physical model exists inside string theory or framework that explains our universe and hopefully is actaully the TOE!?

 

[arivero]

http://www.nature.com/nature/journal/v403/n6767/full/403241b0.html

paid link, sorry.

 

[arivero]

http://www.nature.com/nature/journal/v403/n6767/full/403241b0.html

paid link, sorry.

Furthermore, the link sends to other paid link:

http://www.nature.com/nature/journal/v323/n6089/abs/323595a0.html

Review Article
Nature 323, 595 - 598 (16 October 1986); doi:10.1038/323595a0

The superstring: theory of everything, or of nothing?

John Ellis

Theory Division, CERN, CH-1211 Geneva, Switzerland

Superstring models excite theoretical physicists because they may unite the four fundamental forces. These theories are formulated in a ten-dimensional world of extraordinarily high energies. Recent work indicates how superstrings may nevertheless relate to our four-dimensional world and to laboratory experiments.

So, at least according J Ellis, the term TOE is born explicitly to address superstrings.

It is also used by Veneziano early in 1986 and by M. MITCHELL WALDROP in the journal "Science", 20 September 1985, in the same context. And then before, again by J Ellis in
http://scholar.google.es/scholar?hl=en&lr=&cluster=2576344060349484959
From the Standard Model to Grand Unification
J. Ellis
Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences, Vol. 304, No. 1482, Gauge Theories of the Fundamental Interactions (Jan. 29, 1982), pp. 69-86

Perhaps there is a theory of everything (TOE) that predicts the effective 0 measured
on some very large momentum scale (Ellis & Gaillard 1979)

Before 1980, google scholar
http://scholar.google.es/scholar?hl...erything"&as_ylo=1000&as_yhi=1980&btnG=Search
has 21 links for the expression, of them only a couple about elementary particle physics.

 

[pivoxa15]

String theory is the only 'deep' or mathematically challenging theory today worthy of TOE?

History is on the side of deep theories?