Why are Particle Physicists still searching for the hypothetical 'Graviton'?

Question

As Einstein Theorized (And practically proved) That space time is curved/bent by objects with mass.
Now These curves in space-time are bent in such a way that when an object moving according to its own inertia passes by it, The object's path will be bent (relative to an observer not in an area of bent space-time) and the object may be trapped in orbit.

Now a colleague I was talking with said that he believed that bent space time was the physical consequence of a 'Gravitational field', mediated by gravitons.

However i personally believe that gravity IS bent space-time and there is no other cause besides the fact that matter is bending space-time.

Another problem i have with this is that it would mean all paricles, quarks, leptons, hadrons, etc would all make virtual gravitions, and it would be pretty hard not to detect them considering they should be everywhere around us.

Is there any proof or leads that give Theoretical physicists any knowlage that gravitons may exist at all?
Isnt the fact that what we consider gravity, is just curved space time, discredit it as a force and should be more or less considerd to be 'Disguised' as a force, since there is no 'field' nor is there a force carrier, so curved space-time is just mimicking a force/field ?
Thanks!

Answer 1

Why are Particle Physicists still searching for the hypothetical 'Graviton'?



Of the four fundamental interactions (electromagnetism, gravity, nuclear weak force, nuclear strong force), the gravitational interaction is the only one that hasn't been successfully quantized (written as a quantum field theory). Basically, once you try to do it in the bread-and-butter way done for the other three, you start getting senseless results such as probabilities above 100% or negative probabilities. That's almost as bad as getting 1=0 in your math classes.



With string theory, there seems to be a way to get the quantization of gravity "naturally", provided you admit some weird new math conditions such as additional dimensions; it's not too high a price to pay. The problem is coming up with a way to test those predictions (and compare, with the standard model, the predictions that string theory does for other interactions); that has been a thorn on the side of string theorists. Listen to this: http://www.youtube.com/watch?v=PpQngpaHamg



The quantization of the gravitational field implies that the gravitation field has "excitation modes" which are called "gravitons"; the same way that the electromagnetic field has "excitation modes" called "photons"; and other fields have their own interaction particles.





Is there any proof or leads that give Theoretical physicists any knowlage that gravitons may exist at all?



As far as I know, there are no DIRECT experimental evidence yet that supports a quantized theory of gravity -- be it string theory or something else.



However, a good portion of theorists like string theory because it allows that quantization, not only of gravity but also of other interactions. Other physicists don't like it so much because it looks "ugly" and cumbersome (and it is a bit of a pig; but even the Standard Model isn't too cute either).



But hey, Nature doesn't have to conform to our biases...





Isnt the fact that what we consider gravity, is just curved space time,



Yes, but then how do you write the dynamics for space and time?



Classically, you write a field theory as a Lagragian -- a scalar quantity that obeys the Euler-Lagrange equation. http://en.wikipedia.org/wiki/Euler%E2%80%93Lagrange_equation The "behavior" of a system is such that its evolution minimizes the time sum (technically, the integral over time) of the Lagrangian over the "path" it follows as it unfolds. For example, if you want to know what is the trajectory a planet takes around the Sun, or that a marble makes around a bathtub, or how light bends or is reflected as it travels in transparent media -- if you have a Lagrangian describing the dynamics of the system, then the actual trajectory will be such that the sum of the values of the Lagrangian over the time you observe is the least possible (all other possible trajectories will have a Lagrangian integral that is never LESS than that one).



"Quantically", or better yet, in quantum field theory parlance, you also have an Euler-Lagrange equation; but in place of positions and velocities (which appear in the "classical" flavor of the equation) you have FIELDS (which take the part of positions) and the variation of those fields in time (which take the part of velocities). The equation look wierd, but it's still an Euler-Lagrange equation. And to calculate how the system evolves? You integrate over ALL POSSIBLE "trajectories" that it can take; the "true" trajectory is the one that minimizes the Lagrangian, and all the other trajectories interfere with themselves to cancel each other out and leaving only the "real" trajectory.



OK, that's the bread-and-butter recipe to write a quantum field theory. It works for electromagnetism (very well), it works with the nuclear weak interaction (takes some more work), it works with the nuclear strong interaction (takes some more work). You overlap the three together -- and you have a Lagrangian which is the Standard Model Lagrangian: the sum of each three Lagrangians.



Try the recipe with gravity? Boom.



Regardless of that: those theories describe the interactions of particles (through the Lagrangian) and not the behavior of spacetime. In fact, in the classical lagrangians you write the E-L equation as derivatives relative to those quantities which you want to "bend", space (positions) and time. How are you supposed to describe a dynamics of those coordinates themselves?! It's like trying to lift yourself by pulling on your ankles... I don't see how it might be done!

Answer 2

There is no difference in explaining gravity using the graviton way and not the space time way. You should know that the curvature of space time is not really what we imagine in our brain as a picture of a ball sitting in the fabric. It is much complicated then it is. Space time is bent everywhere due to the presence of the mass and the force itself is carried in the form if information. Just curvature and bending wont cause gravity. The information about bending and telling the object how to move according to this bending is carried by gravitons, which are massless particles and travel with the speed of light.



Gravitons can be found through particle accelerates. I won't go into the detail so just google how gravitons can be found using particle colliders.



We have to present the concept of gravitons and force carrier particles because quantum mechanics don't like relativity so far and both work perfectly on their own. We need to combine these theories to answer your question completely.

Answer 3

In Switzerland, they've constructed a giant desktop to collide particles, in hopes of discovering the particles, from our universe, which might be responsible for life on earth and in the universe. I've read concerning the desktop, and watched a T.V. Episode on the computing device; it's fairly tricky. As a few of folks who answered mentioned the media coined the phrase "God Particle", this isn't genuine. Scientists have also said they hope to find the God particle (possibly in mock might be now not). What you'll find from this laptop is big quantities of nuclear waste. That is why the machine is buried so deep underground. In my view, if this science produces whatever worth while, similar to enormous amounts of power, they are going to most likely use the energy for conflict; the long island project on steroids. Peace. Rather, the God particle that eludes mankind is a non secular peace for all creatures gigantic and small; Revelation 11:18, and 21:three-4

Answer 4

We beleive (at this point of time) that there are 4 forces in nature. But all of them setting up their own force fields follow the general formula for the strength (force), by the product of two (elements) & varying as per inverse square law. So, the formula

F = G(m₁m₂)/r²

is same, with m₁, m₂ (masses) getting replaced by q₁, q₂ (charges) or some other such pair, to formulate a force field. In Electromagnetic theory lot of advancement took place. We are able to characterise the mechanism of generation of waves (we are at it for the past one century or so), the mathematical technques needed (Wave equation, Fourier analysis, Impedance functions etc) that we want to replicate in the case of Gravitation field also. As a step now, we would want to have a Gravitational 'anolog' for a 'Photon'. That we named as 'Gravitons' (the humans are suckers when it comes to 'naming', the only thing they have been doing through out their conscious history). The Space-fabric formulation of the problem is either intractable or inadequate or proving to be so. We have to find a way about it.

Mathematical modeling is an art. Properly handled, it would lead on to comprehensible results like what JC Maxwell did in arriving at the speed of light (in fact 'Electromagnetic waves' that he later said would be extendable to 'light' also - how naive he could be at that time!) from the media characteristics ε, μ. Else, we keep going round in circles, spewing out newer interpretaions that may not be comprehensible. Ultimately, it should appeal to the sense of 'simplicity'. Everything (in Mathematics) starts as a two-dimensional graph of two quantitites; the independent varable on X axis & the dependenet varaible on Y axis. In curved Space, a 'well' is a representation of energy that the energy is negative there (horribly so in case of a blackhole ). Its a mere representation & not a 'physical' well at that particular set of geometrical co-ordinates.

If there is a Force, there is an associated field; if there is a field the Force is defined at a point, (x, y, z) or (w, x, y, z) or whatever. A Wave results (in a wave equation) when a vector operator (∇) while associating 'time' also, defines the wave. So, a wave is a 4D thing. A vector operator is a 3D device (I wonder how one can extend it to higher dimensions). What next?

Answer 5

Here's an article about the Tevatron discovering graviton candidates; the mass they're seeing is barely possible for the Higgs boson but much more likely for the graviton.

http://www.science20.com/quantum_diaries_survivor/cdf_discovers_graviton



That was published in 2010 so the follow-up is probably underway as we speak at the Tevatron and LHC.

Answer 6

What I don't understand is how these theoretical Gravitons can be emitted from an obect; travel one direction through space (at the speed of light, btw) with momentum in the direction of their travel; come into contact with another object; and then magically turn the momentum they have going one direction into a force that pulls the contacted object in the opposite direction.



It just doesn't make any sense, to me.

.

Answer 7

They keep looking because current theory does not demonstrate (or does not adequately demonstrate) that their existance is unnecessary or impossible.

Come up with a convincing mathematical proof of the same, and the search will dwindle away.



(Notice there aren't very many serious scientists still looking for the 'ether' of space. since the Michelson-Morley experiment)

Answer 8

You can't prove a hypothesis to be correct, you can only disprove it. Similarly you can not prove something doesn't exist, you can only prove that it does. If you found a graviton, some hypothesizes would be disproven or need to be revised and that's what the scientific process is about , not just taking things on faith alone.

Answer 9

"Andrew, can you please link to to this alleged proof of gravitons in particle accelerators? otherwise your argument has no validity here."



Actually, his argument could very well be valid without evidence. You seem to be questioning the "Soundness" of his argument, not validity, which deals with the structure of the argument.

Answer 10

The Tevatron shut down. :(

Answer 11

Because if they had found it, they would not have to keep looking.