Why Even Talk About Gravitons Even Existing?

Chronos

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.

twofish-quant

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).

But it does.

twofish-quant

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

That's a observational quirk. Any experiment that has been done at the atomic and subatomic levels shows gravity working there too.

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).

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

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

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

...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

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

Just a small problem there. Maybe within our lifetimes we'll see it.

NYSportsguy

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

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

Maybe I'm rather the uncomplaining type of guy?

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.
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

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

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

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

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

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.