What is the evidence for GR and against the graviton theory?

[UnicycleGuy]

Puzzled by "anti-relativists"

Right off the bat, I'm sorry if this is the wrong forum. I joined to ask this question.

What is the story with the apparently large contingent of people who seem to be in denial about SR and GR, and endlessly belittle Einstein's part in creating them? I sort of understand creationists, though I do not share their views, but used to think such people had little to say on physics. As with creationists, no amount of experimental confirmation will ever convince them that they are wrong. Are they anti-semites, religiously inspired, morons, mavericks or all of these?

I have recently entered into a debate with someone who holds some rather strange ideas, but is at least polite. The good news is that this has caused me to dust off my copy of 'Gravitation', and to refresh and improve my (qualitative) understanding of GR. I'll leave the number crunching to people with larger brains. :-)

Maybe I should just walk away, but I prefer The Enlightenment over the Dark Ages.


UnicycleGuy

 

[NeoDevin]

They don't like things that run counter to their intuition.

 

[mgb_phys]

They would deny Quantum Mechanics too except they don't understand it

 

[Kurdt]

They would deny Quantum Mechanics too except they don't understand it

I wasn't aware they understood relativity either.

 

[RonL]

I think one of my biggest change points was when I started thinking, "what was going on before God put the rainbow in the sky?"

 

[UnicycleGuy]

I could sit here all day and call such people morons and whatnot, but that's not what I'm after. There are lots of things I find counter-intuitive, including SR, but I don't construct gigantic fallacious arguments in some kind of attempt to de-legitimise or undermine them. What is the ultimate motivation? Is it political, religious, racist, financial? Maybe they don't know. I saw this pile of garbage yesterday: http://www.relativitycollapse.net . It is passing strange.

My own debate is/was with an individual who seems to find answers to all of the Universe's mysteries in obscure and unsupported claims about plasma. I guess we need mavericks because every now and then they might be right. But not this time, eh?


UnicycleGuy

 

[Huckleberry]

Without explaining more specifically what their objections are you won't receive valuable answers to your question. The best you could hope for is speculation on speculation. If 'strange ideas' is as descriptive as you can get then you have the answers you were looking for.

edit - maybe try asking this question on a site that is anti-relativist. I'm sure they would be more than happy to tell you exactly what their objections are. Until then the answer is always 42.

 

[UnicycleGuy]

Without explaining more specifically what their objections are you won't receive valuable answers to your question. The best you could hope for is speculation on speculation. If 'strange ideas' is as descriptive as you can get then you have the answers you were looking for.

Well, that's a fair point. I'm not really interested in how A justifies his claim that spacetime curvature is meaningless, B's denial that GPS involves regular relativistic corrections, or what C says to "demonstrate" that Einstein was a plagiarist, etc. I'm more interested in the ultimate motivations for these activities. It seems utterly bizarre to make such claims in face of countless confirmations of the theory. Just more creationist types...

I suspect this is a pointless quest, so I withdraw the question.


UnicycleGuy

 

[mgb_phys]

I wasn't aware they understood relativity either.

no but E=mc2 is easier to write on a poster than

(see even I couldn't get the tex to work out!)

 

[Janus]

I could sit here all day and call such people morons and whatnot, but that's not what I'm after. There are lots of things I find counter-intuitive, including SR, but I don't construct gigantic fallacious arguments in some kind of attempt to de-legitimise or undermine them. What is the ultimate motivation? Is it political, religious, racist, financial? Maybe they don't know. I saw this pile of garbage yesterday: http://www.relativitycollapse.net. It is passing strange.




UnicycleGuy

The difference is that you seem to be able to accept that some things can be counter-intutitive and still be correct.
Many of these others however, suffer from chronic "teenageritis"; the belief that they already know everything and that all "authority figures" are idiots.

 

[sylas]

no but E=mc2 is easier to write on a poster than

(see even I couldn't get the tex to work out!)

You want this T-shirt:

 

[Kurdt]

Write the operators out in full why don't you.

 

[russ_watters]

I wasn't aware they understood relativity either.

They understand just enough to not like it.

 

[TheStatutoryApe]

I think that for just about anyone who would devote their life to science their greatest dream is to do something grand and "shake the foundations". Disproving long held theories, as many great scientists in history have done before them, would fit the bill quit nicely.

 

[OAQfirst]

You want this T-shirt:

Where can I get that?

 

[Ivan Seeking]

I think Janus hit the nail on the head. Some people can't seem to accept that their perception of the world is fallible. There is also a confidence issue. If one doesn't study physics and gain an understanding of how we got to where we are today, it is impossible [for many people] to make the leap of faith and trust science when theory contradicts intuition.

What adds to this problem are those times when science is wrong or incomplete. Two examples come to mind: I was taught that it was a fact that the expansion of the universe is slowing down. There were no qualifiers. It was taught as an absolute fact. In all honesty, I felt a bit betrayed by science when later I learned that an accelerating expansion was within the margin of error all along. Why weren't we told that thirty years ago? Apparently the correct assessment would have been that the expansion could be slowing down, speeding up, or it could be a constant. Could it be that science education showed a bias in order to support the BB Theory?

Another example would be the realization that we had missed 70-90% of the universe. WHOOPS! Talk about egg on the face. To scientists and science lovers, it was a grand discovery. To others, it was just more evidence that scientists take themselves too seriously.

To me the lesson here is not to be so cock-sure that we know as much as we think we do. I love science and physics, so I can only imagine the effect that these discoveries had on people who don't.

 

[Kronos5253]

Where can I get that?

I second that question lol

To the OP:

If it's for the purpose of a discussion with a friend, if you want to prove them wrong, start by assuming they're right.

 

[chroot]

Generally, such people are ignorant about the scientific method. If you talk to them long enough, they will all eventually demonstrate one or more of the following:

1) They do not understand that science only seeks to make models which can predict the outcomes of experiments.

2) They confuse science with philosophy, and make the unreasonable demand that science also explain why its models work, in some form of meta-argument.

3) They do not understand that a model is, in fact, an explanation in and of itself, and no meta-argument is required.

4) They do not understand that any two theories which predict all the same outcomes are, in fact, the same theory, though perhaps dressed up in different mathematical formalisms.

The arrogance and distrust of authority they commonly display is really orthogonal to their misconceptions about science; many scientists also display arrogance and distrust of authority.

So, crackpots are really those who suffer from both arrogance and ignorance simultaneously. Their arrogance is usually much more strongly vocalized, though, and it's so annoying that it usually becomes the entire focus of any debate with them.

From their perspective, any scientist they speak with gets angry and smug, and that reaction only cements their belief that they are winning the debate. It creates a positive feedback loop, where arrogance begets more arrogance. Eventually, they stop caring about the science and focus entirely on the human interaction, and are forever lost.

The same situation happens in many other contexts -- people who feel strongly about religion or politics can become "religious crackpots" and "political crackpots" by exactly the same mechanism.

- Warren

 

[Saw]

I myself, of course, think that SR and GR are correct or at least correct enough to be the foundation for the enormous progress that science and technology have experienced since the advent of those theories (I put this caveat just because sooner or later an evolution/improvement must exist; it's always like that; otherwise, relativity as we know it today would not exist and we'd still adhere to the Galilean mindset).

But it must also be noted that the way science is usually popularized does not help. I suggest you count the number of times that divulgation books use the adjectives "puzzling", "startling", "unbelievable", "incredible" or propose that you should dispense with your logic... It's not rare that people end up being puzzled when they are insistingly being told that something is puzzling. It's not strange that some people object being ordered to dispense with logic and common sense.

As to relativity being counter-intuitive..., I think it is the other way round. It is extremely intuitive: it is the one-shot realization that, even if light does not take the motion of the source, all physical phenomena still conform to the principle of relativity, even if you don't know the logical path that you must traverse to reach such conclusion. That is what an intuition is: you know the answer, you don't know how you got it.

I think that many contenders against relativity would not contend if students or laymen were simply told: Einstein, who was a very intuitive man, made some postulates that "appear" to contradict common sense. But these postulates have been corroborated by experience. So there must be a logic in them, which has not yet been fully unveiled. You are invited to seek that logic and certainly that should boost our understanding of current theories and, who knows, it might even facilitate dvelopments. It is not strictly necessary to fully understand the ultimate causes of phenomena to make science. Very often a pure mathematical formulation of the values that we measure with our instruments suffices to do wondrous things. But of course a better logical understanding of the mathematical concepts and of the measurement process would be welcome...

In this sense, I do not understand why people define Einstenian and Lorentzian (aether) relativity as conflicting and competing theories. For me there is no such opposition. It simply happens that the former provides some easy rules to make science without wasting time on pondering over why the tricks work. That is the beauty of intuition. If you are in a desert and have a dog that finds water by instinct, you'd better trust it if you wish to survive. But, given more time, there is nothing wrong with making some geological investigation. The same applies to relativity: I only need a few formulas to predict that a muon created at the upper atmosphere will hit the surface, but it still seems advisable to keep investigating why it is so, on the basis of the aether hypothesis or any other hypothesis that you may feel like "framing"...

 

[OAQfirst]

Generally, such people are ignorant about the scientific method. If you talk to them long enough, they will all eventually demonstrate one or more of the following:

1) They do not understand that science only seeks to make models which can predict the outcomes of experiments.

2) They confuse science with philosophy, and make the unreasonable demand that science also explain why its models work, in some form of meta-argument.

3) They do not understand that a model is, in fact, an explanation in and of itself, and no meta-argument is required.

4) They do not understand that any two theories which predict all the same outcomes are, in fact, the same theory, though perhaps dressed up in different mathematical formalisms.

The arrogance and distrust of authority they commonly display is really orthogonal to their misconceptions about science; many scientists also display arrogance and distrust of authority.

So, crackpots are really those who suffer from both arrogance and ignorance simultaneously. Their arrogance is usually much more strongly vocalized, though, and it's so annoying that it usually becomes the entire focus of any debate with them.

From their perspective, any scientist they speak with gets angry and smug, and that reaction only cements their belief that they are winning the debate. It creates a positive feedback loop, where arrogance begets more arrogance. Eventually, they stop caring about the science and focus entirely on the human interaction, and are forever lost.

The same situation happens in many other contexts -- people who feel strongly about religion or politics can become "religious crackpots" and "political crackpots" by exactly the same mechanism.

- Warren

This is one of the most insightful and intelligent explanations I've ever read on this issue.

 

[gel]

http://en.wikipedia.org/wiki/Herbert_Dingle" .

I suspect that in many cases it is actually an abnormal psychological condition.

 

[junglebeast]

General relativity is only one hypothetical explanation for gravity. The graviton is another. I personally find the evidence for gravitons to be much more convincing. I've spoken with several physicists on the matter, none of which have been able to point to any evidence that strongly supports GR over the standard model. I therefore classify belief in GR in the same category as belief in God: faith, or pseudo-science at best.

 

[gel]

I personally find the evidence for gravitons to be much more convincing.

So you find zero evidence to be more convincing than a lot of very accurate data agreeing with GR? Very odd.
not that they are inconsistent anyway. Quantum gravity theories, which involve the gravition, are merely refinements of GR in regimes in which GR is expected to break down (as all existing theories must at some point - no serious scientists believes that any current theory is a complete and final theory of everything, afaik)

 

[mgb_phys]

I therefore classify belief in GR in the same category as belief in God: faith, or pseudo-science at best.

Except that my GPS stops working if I don't believe in GR, it continues to work if I don't believe in Santa Claus (oddly my DVD player does stop working - but I blame Disney)

 

[gel]

(oddly my DVD player does stop working - but I blame Disney)

me too. Not GR related, just the damn region encoding.

 

[russ_watters]

General relativity is only one hypothetical explanation for gravity. The graviton is another. I personally find the evidence for gravitons to be much more convincing. I've spoken with several physicists on the matter, none of which have been able to point to any evidence that strongly supports GR over the standard model. I therefore classify belief in GR in the same category as belief in God: faith, or pseudo-science at best.

You should reread warren's four points in his post above! You are drawing-up a conflict that doesn't exist. Any future theory of gravity will necessarily be mathematically identical to GR at least insofar as every experiment performed to date could tell.

 

[junglebeast]

So you find zero evidence to be more convincing than a lot of very accurate data agreeing with GR? Very odd.
not that they are inconsistent anyway. Quantum gravity theories, which involve the gravition, are merely refinements of GR in regimes in which GR is expected to break down (as all existing theories must at some point - no serious scientists believes that any current theory is a complete and final theory of everything, afaik)

1) GR was proposed to explain the bending of light by gravity. Although it was a WACKY idea, people chose to accept it because it explained the observable events when nothing else did. Also, people may have been more open to the concept in light of the current political situation.

2) It was discovered that all of the other fundamental forces are mediated by gauge bosons in the standard model, and all of their associated bosons have been observed. This theory makes intuitive sense.

3) The idea that gravity may also be mediated by a boson is logical, and was proposed, but since we already have a working model for gravity and we can't find a graviton...GR stays. Of course, we have no equipment capable of detecting the graviton, so we have no way to disprove GR.

4) The evidence for GR is not actually evidence for GR. It's really just evidence that gravity bends light. But the graviton can also explain that.

Of course GR works mathematically, because mathematically, you can think of the coordinate system as moving or you can think of the things within the coordinate system as moving. But just because the math works out the same for a moving coordinate system doesn't mean that's what's actually happening.

So as far as I can tell, both theories explain the observations, and the only reason to believe in GR is it was proposed first. By Occam's razor, why should I believe in a theory that requires a completely non-intuitive perspective of warping spacetime, when there's another theory that uses the completely intuitive concept of gauge bosons, which has already been proven for the other forces?

 

[matt.o]

Gravity bends light? I thought that light travels on null geodesics, which happen to be a curved path when a mass is present.

 

[mgb_phys]

1) GR was proposed to explain the bending of light by gravity. Although it was a WACKY idea, people chose to accept it because it explained the observable events when nothing else did. Also, people may have been more open to the concept in light of the current political situation.

The equations predict behaviour that is observed. This doesn't mean the theory is correct - but there aren't any other theories that give correct observations.

This theory makes intuitive sense.

Because a 2m tall plains dwelling ape will have really good intuition about the nature of space time

Of course, we have no equipment capable of detecting the graviton, so we have no way to disprove GR.

We also have no theory of gravitons that give the same behaviour as GR

4) The evidence for GR is not actually evidence for GR. It's really just evidence that gravity bends light.

Thats true of any theory, all a good theory can do is make testable predictions.

 

[junglebeast]

You should reread warren's four points in his post above! You are drawing-up a conflict that doesn't exist. Any future theory of gravity will necessarily be mathematically identical to GR at least insofar as every experiment performed to date could tell.

What you say is only true if we continue to theorize without making new experiments. It is certainly possible that new experiments may be devised that show a discernible difference between GR and some new theory that has approximately the same effect as our current model but differs, for example, in the center of a black hole, or at the big bang, or across cosmic scales like trillions of light years, or at the quantum scale, or that gravity is quantized. If we observe a graviton, that's a measurable difference. There certainly are measurable differences between GR and the graviton, it's just that we can't measure them yet. That doesn't make GR correct.

 

[junglebeast]

We also have no theory of gravitons that give the same behaviour as GR

It's not necessary to have a theory which gives the same behavior as GR -- it's only necessary to have a theory that gives the same behavior for the outcome of the experiments. Can you cite 1 experiment in which GR predicts a result that can be verified, which would violate the graviton model?

 

[mgb_phys]

It's not necessary to have a theory which gives the same behavior as GR -- it's only necessary to have a theory that gives the same behavior for the outcome of the experiments.

Isn't that the same thing ?
behavior = observation = outcome of the experiments.

Can you cite 1 experiment in which GR predicts a result that can be verified, which would violate the graviton model?

Does the graviton model give any predictions?
My understanding (I'm not a particle physicist) is that the graviton model consists of taking the predictions of GR and determining what properties a graviton would have to match them.
Of course that doesn't mean it's wrong, a graviton would have to have these same effects - it's just a suspicious way of going about it.

 

[russ_watters]

What you say is only true if we continue to theorize without making new experiments.

We are making new experiments all the time! The limitation right now is only in the technological power we can currently wield to conduct these tests.

It is certainly possible that new experiments may be devised that show a discernible difference between GR and some new theory that has approximately the same effect as our current model but differs, for example, in the center of a black hole, or at the big bang, or across cosmic scales like trillions of light years, or at the quantum scale, or that gravity is quantized.

Quite true - you aren't disagreeing with me.

If we observe a graviton, that's a measurable difference.

Ok...

There certainly are measurable differences between GR and the graviton, it's just that we can't measure them yet. That doesn't make GR correct.

No, what makes GR "correct" is that it matches the observations of every experiment yet devised to challenge it. And finding a graviton doesn't necessarily contradict GR if it is outside the scope of what the math of GR can predict.

 

[junglebeast]

Isn't that the same thing ?
behavior = observation = outcome of the experiments.

I said that in response to, "We also have no theory of gravitons that give the same behaviour as GR," because you seemed to be indicating that the graviton theory was not a valid competing model. I was pointing out that a theory does not need to give the same behavior as GR in order to be a competing theory. The graviton and GR would both be able to explain all observed behavior, but they both predict slightly different behavior in certain circumstances that we haven't had the capacity to observe yet.

Does the graviton model give any predictions?
My understanding (I'm not a particle physicist) is that the graviton model consists of taking the predictions of GR and determining what properties a graviton would have to match them.Of course that doesn't mean it's wrong, a graviton would have to have these same effects - it's just a suspicious way of going about it.

Essentially yes, but precisely, no. The necessary properties of the graviton can be inferred from the results of GR -- but it's not possible to get the exact same results under all situations using a particle.

 

[Pengwuino]

I think one of the problems is that in the end, there's too much faith involved in most scientific discussion. In our formal education, we "see" the "proof" behind a lot of physical theories hidden behind a jumble of machines and devices that you're told prove some physical law. Honestly, I've never looked at hydrogen radiate, seen the speed of light defy logic, or that a planet bends light. It's quite hard to really come from a first principle and prove something without at some point, making an observable assumption that the person you're teaching has never seen actually proven.

It's really a failure based on just how complex the subject has become. You can't go and build your own particle accelerator and detector from scratch without being told what to do at some point unless you're quite committed to learning the result in isolation through your own initiative. I think the typical physicist just takes assumptions and has faith that if the assumptions are indeed wrong, someone would have pointed it out and proven it wrong.

If someone walked up to me off the street and told me special relativity is wrong, intellectually I could not honestly argue with him, let alone demean them. I know the theory, i know the physics community basically agrees with it and they say it is experimentally verified... but I've never seen it. It almost can feel like a God/no God argument. Oh I believe God exists! Why? Someone told me. You think he doesn't? Why? Someone told you (or you have your own argument which usually isn't logical or relies on arguable assumptions).

Of course, that's just a majority of scientific discussions in my mind... not between experts.

 

[Hurkyl]

I said that in response to, "We also have no theory of gravitons that give the same behaviour as GR," because you seemed to be indicating that the graviton theory was not a valid competing model. I was pointing out that a theory does not need to give the same behavior as GR in order to be a competing theory. The graviton and GR would both be able to explain all observed behavior,

And since (to my knowledge) there aren't any graviton theories that agree with all observed behavior...

(I'm assuming a theory has to be able to make fairly specific predictions before we consider it)

 

[junglebeast]

And since (to my knowledge) there aren't any graviton theories that agree with all observed behavior...

In this framework, the gravitational interaction is mediated by gravitons, instead of being described in terms of curved spacetime as in general relativity. In the classical limit, both approaches give identical results, which are required to conform to Newton's law of gravitation. ... Some proposed theories of quantum gravity[7] (in particular, string theory) attempt to address this issue. In string theory, gravitons (as well as the other particles) are states of strings rather than point particles, and then the infinities do not appear, while the low-energy behavior can still be approximated by a quantum field theory of point particles. In that case, the description in terms of gravitons serves as a low-energy effective theory.

http://en.wikipedia.org/wiki/Graviton

No, what makes GR "correct" is that it matches the observations of every experiment yet devised to challenge it. And finding a graviton doesn't necessarily contradict GR if it is outside the scope of what the math of GR can predict.

By your logic, one could conclude that all theories which explain the same effect can be simultaneously true. That's nonsense! The theories are mutually exclusive

 

[Fredrik]

And since (to my knowledge) there aren't any graviton theories that agree with all observed behavior...

I could be wrong, but I think there's a (non-renormalizable) QFT of gravity (based on the idea of writing the metric as g=\eta+h and only quantizing h) that makes the same predictions as GR if you ignore all the Feynman diagrams that include a loop.

By your logic, one could conclude that all theories which explain the same effect can be simultaneously true. That's nonsense! The theories are mutually exclusive

Don't forget that the only thing experiments can tell us is how accurate a theory's predictions are, or that no theory that's been found so far can possibly be "true".

 

[f95toli]

By your logic, one could conclude that all theories which explain the same effect can be simultaneously true. That's nonsense! The theories are mutually exclusive

There is no such thing as a "true" theory. If two theories give the same result to within the accuracy of an experiment they are both correct in that situation; an obvious example would be SR and classical mechanics. Since most experiments (e.g. all engineering projects except a few notable exceptions such as the GPS) are performed at speeds much lower than c they both agree with experiment (which is why we tend to use Newton's laws most of the time).

Now, SR is obviously valid in situations where classical mechanics is not; but I don't think anyone would argue that Newton's laws are "wrong"; they are simply not valid in all the situations we can test experimentally.

 

[junglebeast]

There is no such thing as a "true" theory. If two theories give the same result to within the accuracy of an experiment they are both correct in that situation...Now, SR is obviously valid in situations where classical mechanics is not; but I don't think anyone would argue that Newton's laws are "wrong"; they are simply not valid in all the situations we can test experimentally.

There is such a thing as a true theory. I think, therefore, I am; therefore the universe is real, and has real laws. It is true that we can never prove one of our made up theories to be exactly in accordance with a true law of the universe, but the goal in science is to keep approaching the truth in the hopes that someday, we actually do know the true laws. Perhaps we are overly ambitious as a species by our pattern of always believing the latest theory up until the point where it is disproven. But once a better theory arises, we can reject an old theory.

Newton's laws are wrong. Undeniably, they are wrong. But they are very good approximations at certain scales, so we still use them as mathematical tools. But it's important to recognize that they are just approximations and we keep in perspective the knowledge of quantum mechanics so that we know where we can and can't use Newton's laws.

GR and the graviton cannot both be true, but one of them might be true. It is logical to continue using GR as a mathematical tool, but it is illogical to believe that GR is correct and can be extrapolated into all circumstances when there are other competing theories sticking their noses out.

Theories of Physics are not only used in the context of the experiments which are used to validate them. They are extrapolated out to situations in which we haven't made observations yet in order to make predictions. They are used to postulate on the origins of our existence in the universe, and they do have philosophical repercussions.

 

[jamesb-uk]

Newton's laws are wrong. Undeniably, they are wrong. But they are very good approximations at certain scales, so we still use them as mathematical tools. But it's important to recognize that they are just approximations and we keep in perspective the knowledge of quantum mechanics so that we know where we can and can't use Newton's laws.

If you believe in quantum mechanics over Newton's laws, then why do you believe in 'the graviton' over GR? Why must quantum mechanics be right, but Newton's laws and GR can't?

I thought the whole point of your argument was that we cannot be certain of any theory, so how can you be certain Newton was wrong, if you are unsure about GR?

 

[Hurkyl]

http://en.wikipedia.org/wiki/Graviton

The next sentence in that article says:

However, attempts to extend the Standard Model with gravitons have run into serious theoretical difficulties​

and this is consistent with my understanding of the situation: we know methods that look like they might give the right answer, but we can't figure out how to make them to work.

(I believe the description there is oversimplified, but I'll let someone more knowledgeable comment on that)

By your logic, one could conclude that all theories which explain the same effect can be simultaneously true. That's nonsense! The theories are mutually exclusive

(I was never talking about "theories which explain the same effect". I was talking about "theories that make agree with observed behavior". There is a difference, y'know: most theories which purport 'explain' some effect get wrong answers)

(1) As the quote said, what makes a theory "correct" is that it matches the observations of every experiment yet devised to challenge it. We use empirical evidence to evaluate the "truth" of our theories, because we don't have some mythical "truth valuation of the universe" which is a function whose inputs are mathematical statements and whose outputs are truth values. Even if such a mythical truth valuation existed, we could never be sure we knew what it was, so it's not a useful concept.

(2) If two theories make exactly the same predictions, then there is nothing to decide between them, no matter how radically different they might appear at first...

(2) But really, you simply aren't being imaginative enough. Go mull over a simple purely mathematical example for a while -- the theory of real number arithmetic and the theory of Euclidean geometry happen to be exactly equivalent mathematical theories.

 

[junglebeast]

If you believe in quantum mechanics over Newton's laws, then why do you believe in 'the graviton' over GR? Why must quantum mechanics be right, but Newton's laws and GR can't?

I thought the whole point of your argument was that we cannot be certain of any theory, so how can you be certain Newton was wrong, if you are unsure about GR?

Newton's laws do not match observations, so they can't be true. Quantum laws do match observations, and there does not exist any other good theory that explains those observations, so to the best of our knowledge quantum theory is true.

GR is one of several theories that matches observations, and the best of our knowledge is not able to rule out other competing theories. Until all but 1 theory can be ruled out, it would be presumptuous to trust any 1 of those contending theories. It would be no different than gambling on which Survivor will win the contest. They aren't all going to win (they aren't all right), but we don't know which.

Whenever there are 2 or more contradictory theories which predict the same results as all experiments (which is the case with GR And the graviton), then none of the experiments can be used as evidence for either theory. It would be like saying, "I heard you talking on the phone today. Therefore, you must have been talking to my sister." No, because it could have been anyone. Likewise, the "evidence" for GR is equally evidence for quantum gravity, and it stops being evidence for either theory over the other. The only evidence that remains for either theory is the fact that the other forces are quantized, which gives a slight edge to the likelihood of quantum gravity.

 

[junglebeast]

The next sentence in that article says:

However, attempts to extend the Standard Model with gravitons have run into serious theoretical difficulties​

and this is consistent with my understanding of the situation: we know methods that look like they might give the right answer, but we can't figure out how to make them to work.

But the next sentence after that proposes a way..

(1) As the quote said, what makes a theory "correct" is that it matches the observations of every experiment yet devised to challenge it. We use empirical evidence to evaluate the "truth" of our theories, because we don't have some mythical "truth valuation of the universe" which is a function whose inputs are mathematical statements and whose outputs are truth values. Even if such a mythical truth valuation existed, we could never be sure we knew what it was, so it's not a useful concept.

(2) If two theories make exactly the same predictions, then there is nothing to decide between them, no matter how radically different they might appear at first...

You are not being logical. Let me try putting this into mathematical terms. A and B are theories, C is observation.

A implies C.
B implies C.
C is true.
You cannot conclude that either A or B is true.

A theory is true under these circumstances only:

A implies C.
Nothing else implies C (so C implies A).
C is true.
Therefore theory A is true.

In reality, we can never prove that "nothing else implies C." We accept a theory as being likely true under this circumstance:

A implies C.
Nothing else that we know of implies C.
C is true.
Therefore theory A is true, to the best of our knowledge.

(2) But really, you simply aren't being imaginative enough. Go mull over a simple purely mathematical example for a while -- the theory of real number arithmetic and the theory of Euclidean geometry happen to be exactly equivalent mathematical theories.

Sorry, but no -- you are confusing theories with theorems. Theories are well-supported hypothesis based on observations, whereas theorems are true by definition. There are no theories in math. A theorem is not accepted until it is proven that it directly follows from other definitions or assumptions under all conditions.

Whereas 2 mathematical theorems may be equivalent, we are not discussing theories which are equivalent. We are discussing theories which are equivalent only up to the presently observed cases. They are not equivalent when extrapolating into all new cases, and are therefore mutually exclusive theories -- NOT just a change in perspective.

 

[Hurkyl]

But the next sentence after that proposes a way..

Sure. But a proposal is merely a proposal.

A theory is true under these circumstances only:

A implies C.
Nothing else implies C (so C implies A).
C is true.
Therefore theory A is true.

In reality, we can never prove that "nothing else implies C."

I've never heard of that logical rule of deduction. Care to provide a reference?

It's irrelevant, though:
(1) "A implies C" cannot be known with certainty
(2) "Nothing else implies C" is trivially easy to disprove. (For example, C implies C)

There are no theories in math.

You lose.

The word is used slightly differently in physics, but none of the differences are relevant to the discussion.

 

[jamesb-uk]

Newton's laws do not match observations, so they can't be true. Quantum laws do match observations, and there does not exist any other good theory that explains those observations, so to the best of our knowledge quantum theory is true.

GR is one of several theories that matches observations, and the best of our knowledge is not able to rule out other competing theories. Until all but 1 theory can be ruled out, it would be presumptuous to trust any 1 of those contending theories. It would be no different than gambling on which Survivor will win the contest. They aren't all going to win (they aren't all right), but we don't know which.

Just because a theory we have is the only one which matches observations, it is not necessarily true- we may very well observe some things in the future which contradict quantum theory- as has happened to many theories in the past. According to your argument, you should feel exactly the same way you do about GR, as all theories which comply with observations.

 

[Tibarn]

The only evidence that remains for either theory is the fact that the other forces are quantized, which gives a slight edge to the likelihood of quantum gravity.

The validity of this argument depends on whether you consider gravity to be a "true" force, which GR does not.

 

[junglebeast]

Sure. But a proposal is merely a proposal.

Well, that's all any theory is -- an idea that was proposed which works to explain observations.

I've never heard of that logical rule of deduction. Care to provide a reference?

If A implies B and B implies A then A = B. I don't remember the name for that logical rule but it's fairly obvious and I shouldn't have to give a reference for it.

The logical fallacy you were committing is called "Affirming the consequent": the antecedent in an indicative conditional is claimed to be true because the consequent is true; if A, then B; B, therefore A.

It's irrelevant, though:
(1) "A implies C" cannot be known with certainty
(2) "Nothing else implies C" is trivially easy to disprove. (For example, C implies C)

(1) A was defined to be a theory which predicts an observation C...so A is chosen by definition to imply C.

(2) It was meant, "no other theory" implies observation "C". An observation is itself not a theory.


You lose.

The word is used slightly differently in physics, but none of the differences are relevant to the discussion.[/QUOTE]

Ok..whatever. There are mathematical theories. But the differences ARE relevant, in the way that I already pointed out, which you ignored.

 

[belliott4488]

junglebeast-

Why do you say that a theory of gravitons (Quantum Gravity) and GR are contradictory? I thought QG is just the proposed quantum field theoretical extension of GR, just as QM is the quantum extension of Classical Mechanics. Not only is QG not contradictory to GR, a fundamental requirement on any graviton theory is that it must match GR in the classical limit, just as QM must reproduce Classical Mech. Do you think that a graviton theory will produce a classical theory other than GR in the appropriate limit? If not, and your preferred graviton theory reproduces all the prediction of GR in all the currently tested energy regimes - how is that a contradictory theory?

I don't know of anyone who says that GR is "true", in the sense of being the only theory of gravity that will ever be needed to predict any conceivable observation. In fact, it's precisely the breakdown of the the theory at the Planck scale that leads us to say that there must be some kind of QFT for gravity - hence the graviton. But GR is the starting point for such theories - they don't contradict it.

 

[Hurkyl]

Well, that's all any theory is -- an idea that was proposed which works to explain observations.

"Proposal" is not synonymous with "an idea that works".

If A implies B and B implies A then A = B. I don't remember the name for that logical rule but it's fairly obvious and I shouldn't have to give a reference for it.

The rule you used was

A implies C.
Nothing else implies C.
C is true.
Therefore theory A is true.​

I decided to analyze it for fun. It turns out that the pair of statements

A => C
For all B: (B => C) => (B <=> A)​

is logically equivalent to the pair of statements

not A
not C​

The logical fallacy you were committing is called "Affirming the consequent": the antecedent in an indicative conditional is claimed to be true because the consequent is true; if A, then B; B, therefore A.

That doesn't resemble anything I said.

(1) A was defined to be a theory which predicts an observation C...so A is chosen by definition to imply C.

Yes, I was wrong -- I was ignoring the degenerate cases. Realistic cases come with uncertainty attached, though.

(2) It was meant, "no other theory" implies observation "C". An observation is itself not a theory.

If your argument is defeated by a degenerate case, it doesn't suddenly become valid if you declare by fiat that we shouldn't consider degenerate cases.