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Why Even Talk About Gravitons Even Existing?

by NYSportsguy
Tags: existing, gravitons, talk
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twofish-quant
#19
Feb18-10, 12:16 AM
P: 6,863
Quote Quote by NYSportsguy View Post
There is no "need" for quantum gravity. That's exactly the point I am trying to make. Why should there be a "NEED" for quantum gravity like you said above?
Because when you apply straight general relativity to certain situations and ask what happens you get the answer "divide by zero" which is no real answer. Once you compress things past a certain point quantum effects start becoming important, and if you exclude quantum effects from things like black holes, you run into problems with things like the second law of themodynamics breaking down, which is a bad thing.

Basically, if you assume that gravity does not have quantum effects, your theories start giving non-sense results (i.e. divide by zero, infinities, answers that don't make any sense).

If gravity has no effect at the quantum level (objects with extraordinary small masses).....why try to unite it with the other three fundamental quantum forces to begin with?
But it does.
twofish-quant
#20
Feb18-10, 12:27 AM
P: 6,863
Here is a cool experiment that illustrates gravity having quantum effects

http://physicsworld.com/cws/article/news/3525

Basically, you create a gravity potential well, trap neutrons in it, and then the neutrons behave the same why as they would in an EM potential well.

Also gravity is weak. It's not non-existent. One of the cooler experiments you can do is the Cavendish experiment where you see gravitation effect of brick sized object.

There is also the Mossbauer effect, which is a standard experiment that shows that yes, gravity does act on particles

http://world.std.com/~sweetser/quate.../redshift.html
twofish-quant
#21
Feb18-10, 12:35 AM
P: 6,863
Quote Quote by NYSportsguy View Post
considering the other three are all strong at the atomic and smaller levels while gravity usually only rears it's head at large mass levels.
That's a observational quirk. Any experiment that has been done at the atomic and subatomic levels shows gravity working there too.

The other three forces use "force fields" of some kind to attract and repel things while gravity really doesn't use any type of "force field" but rather is just physically bending space-time as we know it.
That's just a function of the way that we do the math and probably not a result of the nature of the forces themselves. It so happens that if you really want to, you can show that classical electromagnetism can be modelled as the bending of space-time in 5 dimensional space (which is what Kaluza figured out in the 1920's).

Gravity, on the other hand hand, shouldn't have it's own similar particles like the graviton just for the sake of fitting in with the other three quantum forces.
The problem with having two independent and separate theories is that you then have to explain exactly what happens at the boundary of those theories.
Frame Dragger
#22
Feb18-10, 06:18 AM
P: 1,540
Quote Quote by Chronos View Post
Just trying to help him out, frame dragger. I hoped pointing out the ATM component of his argument would be instructive. It is easy to wander into the ATM mine field. I view this as an innocent transgression until followed by denial of observational evidence.
Hmmm... you're a much better person than I am, or at least a hell of a lot less negative. Maybe you're right... it's just frusterating trying to communicate past the pseudoscience out there sometimes.
der.physika
#23
Feb24-10, 04:08 AM
P: 38
I don't know who said it earlier, I think it was NY-sports but, one of the reasons why gravity should be omitted and separated from The Strong & Electroweak forces was because it has no force field. Well... the thing about that is... the boson fields that the other forces operate in, are "imbedded" in the space-time which is what gravity is, moving or hence curving warping space-time, I think maybe gravity should not be omitted since the other gauge boson fields operate within the space time, gravity is actually the harboring force, enabling the other forces, it's the housing force. Gravitons? Well... I don't think they should be dismissed too fast, I think there must be some merit in quantum gravity theory
Frame Dragger
#24
Feb24-10, 04:29 AM
P: 1,540
Quote Quote by der.physika View Post
I don't know who said it earlier, I think it was NY-sports but, one of the reasons why gravity should be omitted and separated from The Strong & Electroweak forces was because it has no force field. Well... the thing about that is... the boson fields that the other forces operate in, are "imbedded" in the space-time which is what gravity is, moving or hence curving warping space-time, I think maybe gravity should not be omitted since the other gauge boson fields operate within the space time, gravity is actually the harboring force, enabling the other forces, it's the housing force. Gravitons? Well... I don't think they should be dismissed too fast, I think there must be some merit in quantum gravity theory
...but if gravitons DO exist then gravity IS a force field! That's the problem with unifying that notion with your description of GR spacetime. I think it's a good argument for a theory unifying the two being radically different from current theories. Trying to reconcile the two now, requires unreasonable contortions.
Ich
#25
Feb24-10, 04:59 AM
Sci Advisor
P: 1,893
...but if gravitons DO exist then gravity IS a force field!
I don't have a problem with thinking of gravity as spacetime deformation instead of a "force" field, and of gravitons as the quanta of spacetime deformations. The point is that we don't have a theory that works that way. Or any other way, for that matter.
Frame Dragger
#26
Feb24-10, 10:54 AM
P: 1,540
Quote Quote by Ich View Post
I don't have a problem with thinking of gravity as spacetime deformation instead of a "force" field, and of gravitons as the quanta of spacetime deformations. The point is that we don't have a theory that works that way. Or any other way, for that matter.
Just a small problem there. Maybe within our lifetimes we'll see it.
NYSportsguy
#27
Feb25-10, 12:36 AM
P: 104
Quote Quote by Frame Dragger View Post
Just a small problem there. Maybe within our lifetimes we'll see it.
Yea way to add intelligent insight into the conversation there buddy.

To the rest of you, thank you very much for your answers and links for examples. I will look over all of your responses and the links you have provided me and see if I can retort and/or understand better the topic.
NYSportsguy
#28
Feb25-10, 01:41 AM
P: 104
Quote Quote by Ich View Post
I don't have a problem with thinking of gravity as spacetime deformation instead of a "force" field, and of gravitons as the quanta of spacetime deformations. The point is that we don't have a theory that works that way. Or any other way, for that matter.
How can you NOT have a problem with this? There is nothing to prove or suggest that this is the right way to look at gravity at all. Why are you comparing they way light works and behaves to the concept of gravity? Possibly because E = MC^2?

Still not a good enough reason.....I am sure you have another but I would like to hear it.


PS - Your earlier statement seems to be correct. Anything with any mass (no matter how tiny or miniscule by our standards) will exert some sort of curvature on space-time (hence gravity at an atomic level).

Link: http://www.physicsforums.com/archive.../t-118327.html
Ich
#29
Feb25-10, 03:50 AM
Sci Advisor
P: 1,893
How can you NOT have a problem with this?
Maybe I'm rather the uncomplaining type of guy?

There is nothing to prove or suggest that this is the right way to look at gravity at all.
There is nothing to prove it, but the theoretical analysis of gravitational waves in the weak field limit suggests that it's associated with a massless spin-2 particle.
Why are you comparing they way light works and behaves to the concept of gravity? Possibly because E = MC^2?
No, because both follow a wave equation (I'm talking about gravitational radiation here), and QM tells us how to quantize waves. But it doesn't tell us how to quantize the full-fledged nonlinear theory.
Chronos
#30
Feb26-10, 12:35 AM
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I'm stuck on the wave thing. It is difficult to conceptualize gravitational waves without bosons - sort of like an ocean wave without water molecules. Bosons may not be an ideal explanation, but it works for all the other fundamental forces. An effective theory is not necessarily a bad thing. Why it works - that is for our children to solve.
sEsposito
#31
Feb26-10, 05:51 PM
P: 154
Quote Quote by NYSportsguy View Post
From what I have read out there, of the four fundamental forces that have been detected in our universe, gravity seems to be the weakest at the atomic level and smaller.

I figure this is most likely true because at the atomic level and smaller - the weak and strong forces (those causing beta decay and gluons to hold quarks inside of protons and neutrons) are the forces that build matter at an atomic level.

Gravity seems to only rear it's head when the mass of any object is that of an atomic mass or higher. The larger the mass of anything....the more gravity plays a role according to Einstein's general relativity principles.

Therefore gravity is a force that needs to be separated from the other three major forces because it doesn't seem to appear or work at levels smaller than anything smaller than an atom.

If this is all true....then why the need to even talk about mass-less particles like gravitons even existing in the first place? After all, Einsteins' Gen. Relativity Theory says gravity is nothing more than the physical bending or curving of the space-time fabric which anything that has mass on it does. Thus it's nothing more than a force that only shows up when masses are that of an atom or larger and not at the quantum level.
I think the main thing to remember is that while gravity is a very weak force of nature, it still exists. I understand that you're saying "at the quantum level" but you cannot simply ignore a it all together. I think its important to include gravity at the table of quantum discussion because the very fact is that it exists, no matter how strongly or weakly it effects things at the sub-atomic level.

Also, it's important to look far and wide when considering questions like the one that you have posed; if you take away gravity (or stop talking about it) than at some point the math stops working. And that as you know is bad. Gravity has quantum implications, they're just very, very weak.
der.physika
#32
Feb26-10, 06:00 PM
P: 38
Saying that gravity should be ignored from the quantum level and should only be considered with [tex]\geq[/tex] atomic, doesn't make much sense. Because atoms consist of nuclei and other smaller quantum subatomic particles...which all together work together and has a gravitational interaction, although gravity is quite weak it's obviously out there and a very strong force at the macroscopic level. But, the quantum level has to be considered, cause like sEsposito said, the math won't work and that IS bad
map19
#33
Mar1-10, 03:06 PM
P: 88
NYSportsguy.
Gravity is produced by any energy. That includes light.
For ex. the Earth's gravity is produced by its mass-equivalent energy, its rotational energy, its thermal energy, and any other energy i haven't thought of.
The total energy is responsible for the total gravitation.
Mass-equivalent energy is by far the biggest contributor.
http://en.wikipedia.org/wiki/General_relativity
sEsposito
#34
Mar1-10, 04:25 PM
P: 154
In contrast to what the starter set out to accomplish -- this thread has really demonstrated the importance of gravity (especially at the sub-atomic level!)... So many well informed replies.

I think its really cool when I can find the importance in something someone set out to nullify.
qwe
#35
Mar13-10, 10:08 PM
P: 26
In my opinion it seems a bit far-fetched to link gravity to the other three major fundamental forces considering the other three are all strong at the atomic and smaller levels while gravity usually only rears it's head at large mass levels
well ONE of the four forces has to be the smallest of the four, assuming they all aren't the same, right?...
NYSportsguy
#36
Mar17-10, 03:34 PM
P: 104
Quote Quote by sEsposito View Post
In contrast to what the starter set out to accomplish -- this thread has really demonstrated the importance of gravity (especially at the sub-atomic level!)... So many well informed replies.

I think its really cool when I can find the importance in something someone set out to nullify.
To be honest with you.....I posed this question because I wanted to get a thoughtful discussion going. I really wasn't trying to "nullify" anything. My purpose was to get an end outcome that either justified the need to look for "gravitons" or disprove it as a myth.

Either resolution or outcome would have been just fine with me.


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