Physicists - the new theologians

[Chalnoth]

Uhhh. I think that's disputed.

Sorry, I should have used "productive" instead of "promising". And string theory has been quite productive. It is from string theory that we get the idea of supersymmetry, after all, which so far the leading candidate for physics beyond the standard model. It's also been a fountain of ideas for potential (testable) ways in which extra dimensions might exist. And through string theory we've discovered some remarkable aspects of holography, where it turns out that the different string theories appear to exhibit identical physics (though this has so far only been partially shown...the remaining aspects remain promising, but the hard work has yet to be completed).

So, given that string theory has provided us with such a variety of new things to test in future experiments, why should theorists abandon it, exactly?

 

[redwards]

Sorry, I should have used "productive" instead of "promising". And string theory has been quite productive. It is from string theory that we get the idea of supersymmetry, after all, which so far the leading candidate for physics beyond the standard model. It's also been a fountain of ideas for potential (testable) ways in which extra dimensions might exist. And through string theory we've discovered some remarkable aspects of holography, where it turns out that the different string theories appear to exhibit identical physics (though this has so far only been partially shown...the remaining aspects remain promising, but the hard work has yet to be completed).

So, given that string theory has provided us with such a variety of new things to test in future experiments, why should theorists abandon it, exactly?

I didn't say they should. Merely that people who suggest that it is not the answer aren't crackpots.

 

[Chalnoth]

I didn't say they should. Merely that people who suggest that it is not the answer aren't crackpots.

Yes, they are, because they assert this when string theory has so many things going for it. Look, from what we know right now, there are many different potential avenues of theoretical physics research that are quite valid. String theory is one of those avenues. From the evidence available right now, those people that are asserting that string theory is full of bunk are just making specious arguments.

If they want to make a decent argument, they should be making a positive argument for some other approach, because these negative arguments against string theory aren't highlighting anything that string theory does worse than other theories.

 

[redwards]

Yes, they are, because they assert this when string theory has so many things going for it. Look, from what we know right now, there are many different potential avenues of theoretical physics research that are quite valid. String theory is one of those avenues. From the evidence available right now, those people that are asserting that string theory is full of bunk are just making specious arguments.

How is, "your theory is not falsifiable" a specious argument? That seems fairly fundamental, to me.

And where do you get off calling Feynman and Krauss 'crackpots'?

If they want to make a decent argument, they should be making a positive argument for some other approach, because these negative arguments against string theory aren't highlighting anything that string theory does worse than other theories.

There's nothing wrong with calling a spade a spade and acknowledging that string theory has fundamental problems. Nor is there anything wrong with suggesting people divert their attention to finding a different solution instead of continuing to study what appears to be a failed one

 

[Chalnoth]

How is, "your theory is not falsifiable" a specious argument? That seems fairly fundamental, to me.

It's also a problem that so far has faced every beyond-standard-model theory. The basic problem is that nearly all of these theories have some free parameters that could take on values that are far out of the range of detectability. So unless you want to level a critique against all work so far in searching for beyond-standard-model theories, it's an invalid critique.

And where do you get off calling Feynman and Krauss 'crackpots'?

Feynman can be forgiven as he died before much of the exciting stuff in string theory happened. Krauss is apparently entirely for physicists continuing to research string theory, he just doesn't think it deserves acclaim (to which I agree largely...it still is highly speculative, after all). He further admits that there really aren't any good alternatives, so I don't see why he should be quoted here.

There's nothing wrong with calling a spade a spade and acknowledging that string theory has fundamental problems. Nor is there anything wrong with suggesting people divert their attention to finding a different solution instead of continuing to study what appears to be a failed one

As I've said, the theorists who are so convinced string theory is fundamentally flawed should focus their efforts on coming up with an alternative. Unless they can do that, they shouldn't be bothered with these ridiculous negative arguments against string theory. Nobody, after all, is steadfastly asserting that string theory is accurate, merely that it's a worthwhile area of research. And so far, it has proved to be quite worthwhile to theorists.

 

[lawtonfogle]

How is, "your theory is not falsifiable" a specious argument? That seems fairly fundamental, to me.

And where do you get off calling Feynman and Krauss 'crackpots'?



There's nothing wrong with calling a spade a spade and acknowledging that string theory has fundamental problems. Nor is there anything wrong with suggesting people divert their attention to finding a different solution instead of continuing to study what appears to be a failed one

But isn't there a fundamental problem between other well known things, which we just say "We will get around to explaining that in a bit"? Yet, to say that is reason for people to divert their attention to finding a different solution, based off of the underlying argument that if it has problems we can't explain, it could be broken, is wrong. It isn't that they are suggesting that others should try different theories, but the underlying reason for doing so.

 

[ArnautDaniel]

I suggest you stop paying attention to a minority of what are essentially crackpots.

Oh I've studied some String Theory and have some idea who the crackpots are.

I'm still waiting for that paper with a prediction from String Theory that can be compared with experiment.

 

[Chalnoth]

Oh I've studied some String Theory and have some idea who the crackpots are.

I'm still waiting for that paper with a prediction from String Theory that can be compared with experiment.

You do realize, I hope, that there have been oodles of papers that have presented models that stem from string theory which can be directly tested?

 

[ArnautDaniel]

Sorry, I should have used "productive" instead of "promising". And string theory has been quite productive. It is from string theory that we get the idea of supersymmetry, after all, which so far the leading candidate for physics beyond the standard model.

Supersymmetry was floating around when String Theory was just the dream of a physicist with a crack pipe. People were coming up with supersymmetric extensions of the standard model when nobody was working on String Theory.

Of course supersymmetry has its own giant problem:

How exactly is it that we have yet to see any two particles which are super-partners of each other?

Odds are that supersymmetry is probably wrong as well.

Of course the modern physicist-theologian-theorist doesn't care about experiments.

It's also been a fountain of ideas for potential (testable) ways in which extra dimensions might exist. And through string theory we've discovered some remarkable aspects of holography, where it turns out that the different string theories appear to exhibit identical physics (though this has so far only been partially shown...the remaining aspects remain promising, but the hard work has yet to be completed).

So, given that string theory has provided us with such a variety of new things to test in future experiments, why should theorists abandon it, exactly?

Because they can't actually perform a calculation that predicts an actual number that can actually be measured?

Because the theory isn't remotely mathematically rigorous even by the standards of QFT (which has a few rigor problems of its own, but at least calculates numbers that can be compared to nature to justify itself).

Because I too can pick up a crack pipe and come up with nifty ideas like maybe extra dimensions exist and maybe every atom is a solar system of its own and maybe every other physicist is conspiring too suppress my crack pipe dreamed theory?

Look, all people are asking for is a number.

An empirical number.

Even one that can already be calculated using the standard model.

Where is it?

Really?

How can anything call itself physics and not pump out numbers?

Everything else belongs in the philosophy department.

They've had 30 years, they've failed miserably, they need to move on.

 

[Chalnoth]

Supersymmetry was floating around when String Theory was just the dream of a physicist with a crack pipe.

Ah, sorry, I misread the Wikipedia entry, as I had heard this previously.

But it remains the case that supersymmetry is a prediction of String Theory because it doesn't work without it.

Of course supersymmetry has its own giant problem:

How exactly is it that we have yet to see any two particles which are super-partners of each other?

Nearly all of the interesting models predict that we shouldn't have seen any superpartners just yet. Once we start probing into the low-TeV range, then there's a good reason to think that the theory is highly unlikely to be true. Until then, it's at least as likely as other beyond-standard-model theories.

Because they can't actually perform a calculation that predicts an actual number that can actually be measured?

You do realize, I hope, that string theory is a candidate for a theory of everything? Why on Earth do you think it should be easy to determine from a theory of everything what the observable consequences are? Or easy to measure once they are determined?

 

[Maxwell511]

I find it interesting that string theory is so often derided just outside the physics community. Within physics it's typically considered a promising theory that needs a hell of a lot of work. Here are the basic reasons why it's considered promising:

1. String theory is a very mathematically beautiful theory. In the past, seeking mathematical beauty has been a tremendous boon to theorists searching for new theories.

That's extremely subjective. Mathematical beauty is not a valid reason to assume something may be a good reflection of reality.

2. String theory is, as yet, the only candidate fundamental theory that we have. Until somebody can come up with an alternative fundamental theory, or until it is shown that string theory is inconsistent with itself or with reality, string theory will still be a valid avenue of research.

God did it. Plus I believe that the OP mentioned Loop Quantum Gravity one other potential theory.

3. Contrary to popular belief, string theory does make two very significant predictions: it predicts a fully-quantum law of gravity, and it predicts supersymmetry. The former is truly enticing for theorists because until string theory came along, nobody had a clue how to unify gravity and quantum mechanics. But in string theory, the theory doesn't work if you don't have gravity: it predicts it. And it's a fully quantum theory. And supersymmetry may well be detected at the LHC.

In order to survive as a theory of everything string theory is required to predict gravity. The problem with string theory at the moment is that it is a theory of anything. A very beautiful theory of anything but not necessarily right.

Finally, it is well-known among theoretical physicists that string theory is exceedingly difficult. It's soaked up a lot of man-hours just to get to our current understanding of the theory, and there's a lot left to go. It is entirely too premature to claim that the theory is unable to provide falsifiable experimental predictions (in a sense, the two above predictions are not falsifiable, as we already know about gravity, and supersymmetry may not be detected but still exist).

And even if the theory ultimately turns out to be false, the mathematics developed by people pursuing string theory will certainly remain useful to theoretical physicists and mathematicians alike.

Agreed. The mathematics of theories on the diffusion of heat came from fundamentally wrong theories.

 

[Chalnoth]

That's extremely subjective. Mathematical beauty is not a valid reason to assume something may be a good reflection of reality.

Except it's proven to be an excellent guide in the past. And it's not entirely subjective, as in large part it's just another manifestation of Occam's Razor.

God did it. Plus I believe that the OP mentioned Loop Quantum Gravity one other potential theory.

Loop Quantum Gravity is a potential theory of quantum gravity. I don't believe it works as a theory of everything. Now, I will state that at the current time, I don't have enough information to say whether LQG or ST is more likely to be accurate. But ST is quite a lot more than LQG is.

And "God did it" isn't even a theory. At least ST has the potential to act as an explanatory framework.

In order to survive as a theory of everything string theory is required to predict gravity. The problem with string theory at the moment is that it is a theory of anything. A very beautiful theory of anything but not necessarily right.

Which is one reason why I think it's got promise as a candidate theory of everything. While it's not strictly true that it's a theory of anything at all, it does have a mind-boggling number of possible solutions, which I would naively expect to be the case for a "theory of everything", as otherwise we're left with the strong anthropic principle, which is just nonsense. It does, of course, make it fantastically difficult to make predictions from, but I don't think we should expect a theory of everything to be easy.

 

[ArnautDaniel]

Ah, sorry, I misread the Wikipedia entry, as I had heard this previously.

But it remains the case that supersymmetry is a prediction of String Theory because it doesn't work without it.

That isn't a prediction.

A prediction is something that pops out of the theory. Not something you add to the theory because it doesn't work otherwise.

Nearly all of the interesting models predict that we shouldn't have seen any superpartners just yet. Once we start probing into the low-TeV range, then there's a good reason to think that the theory is highly unlikely to be true. Until then, it's at least as likely as other beyond-standard-model theories.

No, all the interesting models that aren't obviously wrong predict we shouldn't have seen superpartners yet.

There are plenty of interesting models that are wrong. And they are wrong precisely because they predict low mass superpartners.

Here, I'm such a nice guy, I'll even give you one.

Take the Standard Model and construct superpartners for every particle and give them the same mass as the original particle.

There the simple supersymmetric extension of the Standard Model.

It is of course wrong, but it is certainly interesting.

The fact is people have to work hard to construct models that don't end up with superpartners that we should have seen already.

Of course this is a big issue as we have no idea why anything has the particular mass it does.

The Higg's may account for mass existing at all, but it doesn't account for the coupling value for each field with the Higg's field, so people are still free to pull those numbers out of their rear.

You do realize, I hope, that string theory is a candidate for a theory of everything? Why on Earth do you think it should be easy to determine from a theory of everything what the observable consequences are? Or easy to measure once they are determined?

I heard a joke once:

There was a guy outside of a movie theater at night looking for his keys under a streetlight. Another guy comes along and helps him for a while.
After they can't find the keys for a while the other guy says:

"Are you sure you lost your keys here?"

The original guy says:

"No, I lost my keys in the theater, but the light is better out here."

That is String Theory in a nutshell.

 

[Chalnoth]

That isn't a prediction.

A prediction is something that pops out of the theory. Not something you add to the theory because it doesn't work otherwise.

Since any theory requires mathematical consistency, it's a prediction.

No, all the interesting models that aren't obviously wrong predict we shouldn't have seen superpartners yet.

Sure, but so what? Once we get past the really obviously wrong models, trying to solve the hierarchy problem often leads to masses in the TeV range.

I heard a joke once:

There was a guy outside of a movie theater at night looking for his keys under a streetlight. Another guy comes along and helps him for a while.
After they can't find the keys for a while the other guy says:

"Are you sure you lost your keys here?"

The original guy says:

"No, I lost my keys in the theater, but the light is better out here."

That is String Theory in a nutshell.

I don't see how.

 

[ArnautDaniel]

Since any theory requires mathematical consistency, it's a prediction.

Bosonic string theory isn't mathematically consistent?

No. It is mathematically consistent (well as mathematically consistent as any string theory is, given their dubious mathematics)

So since there are consistent string theories without supersymmetry, it isn't a prediction.

Sure, but so what? Once we get past the really obviously wrong models, trying to solve the hierarchy problem often leads to masses in the TeV range.

So now you've moved the bar, it isn't "interesting", now it is "not obviously wrong".

So all you are saying is that all the not obviously wrong models (i.e. models that don't have low mass superpartners) predict that that low mass superpartners don't exist.

Wow. That is truly profound.

Anyway the complete lack of an observed partner-superpartner pair leads one to suspect that supersymmetry may well not be part of nature.

Is there any other reason to hold out for supersymmetry beyond that one can't get string theory to work without it?

It really looks suspiciously like another reason to doubt string theory.

I don't see how.

Of course you don't.

You've drunk the kool-aid

 

[Chalnoth]

Bosonic string theory isn't mathematically consistent?

It's got a tachyon in it, which is completely nonsensical.

 

[ArnautDaniel]

It's got a tachyon in it, which is completely nonsensical.

It is still mathematically consistent.

You said that supersymmetry was a requirement to make a string theory consistent and so was a prediction.

I simply pointed out the fact that there are consistent non-supersymmetric string theories.

The fact is supersymmetry is introduced as a postulate to make things go so it isn't a prediction of the theory.

...

Let's take a look at things:

Okay so one finds that given a string theory, that by imposing supersymmetry on it one can get a theory with both bosons and fermions (the other thing bosonic string theory has problems with), and not tachyons.

Fine.

Now none of this proves that this is the only way to get a string theory with bosons, fermions, and no tachyons. There could well be a whole family of symmetries out there that does the same thing - heck maybe if we looked carefully we could find a member of this family that would do something sensible like make the theory have 3 physical dimensions and 1 of time.

So no, you aren't predicting supersymmetry, you are just saying that by supposing supersymmetry at the outset one can get a theory with certain nice properties

None of this makes supersymmetry proven or right.

So, we suppose supersymmetry...which means we are supposing at the outset that there are a whole lot of particles that exist that we have never observed...

...okay and from that we get a theory that has bosons, fermions and no tachyons and...well...requires 10 dimensions.

So now we are supposing a whole mess of particles no one has observed and dimensions no one has observed.

But...we say...but we have a theory that contains a quantum gravity...or seems to...kind of...but we can't really demonstrate that because we can't calculate anything, but it looks kind of like it should be what we think a quantum gravity should look like...

...of course what we think a quantum gravity should look like, and what nature might really do can be entirely different.

Okay so we've got this theory we can't calculate anything in that proposes there are particles we have never seen and dimensions we have never seen...and...

...and it requires these dubious things called "branes" which never existed in the previous models (i.e. the Standard Model), and also have never actually be detected, so now, in addition to all these particles and dimensions we've never seen we've got a new type of object we've never seen.

Why are branes proposed? Because they are needed to make what string theorists pretend are calculations go forward.

Okay so we've got particles, dimensions and branes that no one has ever seen, and maybe a quantum theory of gravity...but wait, there is still the pesky matter of getting the Standard Model (appropriately supersymmetrically extended mind you) to pop out. So to do this we must construct dubious Rube Goldberg Machines involving carefully placed branes and strings running along them.

Of course there is no proposal to explain why exactly the branes would be placed so conveniently.

...and of course I'm leaving out things like Calabi-Yao Manifolds and the "Cosmic Landscape" which would appear to claim that every possible universe exists, and that of course our Rube Goldberg Machine Standard Model satisfying universe must exist because, since everything possible is going on, this has to happen just because of the odds....

 

[Chalnoth]

I don't see how a theory with an unstable vacuum can honestly be considered consistent.

 

[ulu]

When under stress I repeat myself, when under stress I repeat myself When under stress I repeat myself, when under stress I repeat myself When under stress I repeat myself, when under stress I repeat myself

 

[ArnautDaniel]

I don't see how a theory with an unstable vacuum can honestly be considered consistent.

The general definition of "consistent" in mathematical circles is that you cannot deduce both A and not-A in the theory.

Assuming you have started with a consistent set of postulates and all your mathematical moves are all legitimate, then the theory should be consistent.

That is what good mathematics is all about.

You are either complaining of a consistent theory with properties you don't like, or a theory where someone has made a mathematical error introducing a contradiction somewhere.

Now the latter is possible as bosonic string theory isn't really mathematically rigorous (of course superstring theory isn't either - so who knows maybe you can prove anything in it because it contains a contradiction!)

...but I suspect by "consistent" you mean "remains consistent when we add a certain yet-to-be-named postulate X to the theory"

What is that postulate exactly?