What is gravity?

Backus

From an early age I thought that scientists knew what gravity is, the actual thing and not just the effect it has on us. One time, to my disbelief, I read somewhere that we do not know what it is. I actually have no memory of where I heard that we don't know what it is. Anyway, for the rest of my life from when I discovered that we don't know what gravity is till now, I have just assumed that that was true. We don't know. However, I recently had a teacher who said we do know what gravity is, I forget his explanation though.

So my question is: Do we know what gravity is? If so, what is it? If not, why don't we know, and what do we need to find out?

thank you in advance.

jtbell

How would we know whether it's the "actual thing"?

Chronos

Gravity is the negative reaction of space to the positive energy of matter.

prsww3

Unfortunately, we don't actually know for sure what causes gravity....or even that there is such a thing as gravity . There are theories that involve particles called gravitons but we haven't ever actually observed them.

The truth is that gravity is just a math model that that helps us predict stuff pretty well. Keep a close eye on cern...maybe we'll see some gravitons in our lifetime!

Chronos

Gravitons are virtual particles. We can only infer their existence by their effective action on mass possesing particles. That evidence is pretty compelling right now.

Light Bearer

starzero

This is the real issue. We can describe what gravity is and what it does.

The reason it is there is the real mind blower.

Drakkith

I don't see this as an issue at all. I don't even think it's possible to know whether or not we know what something "really is". If we can accurately predict what will happen using a model, does it matter if the model and underlying theory is "really true" or not? Even if we were able to predict things with perfect precision and accuracy, how could anyone know if we "really" knew what something is?

SHISHKABOB

I think perhaps the problem is that we don't fully understand how a force can act at a distance. I think that understanding how gravity acts at a distance is something that will help further our understanding and help build better models.

Drakkith

Care to elaborate on how we don't fully understand how a force acts at a distance?

SHISHKABOB

It was my understanding that the graviton is a theoretical particle?

Drakkith

Yes, it has not been observed. I'm not sure if the standard model of particle physics even predicts its existence or not.

SHISHKABOB

And so virtual particles are what mediate the fundamental forces, yes?

So it's my understanding that a lack of understanding and a lack of knowledge of the existence of the graviton means that the understanding of how the fundamental force of gravity acts at a distance is not complete.

We have models like Newtonian gravity and General Relativity which describe how it works on macroscopic things, but on a quantum level, we don't have a complete understanding. Or at least, that is *my* understanding. I've only got a rudimentary education of basic quantum mechanics principles.

Drakkith

Only in Quantum theories, not in GR.

I think GR explains it pretty well.

Sure. But we don't know which one is correct for gravity, or rather which one is more correct and which way we should go to develop the next theory or resolve the discrepancies. Keep in mind that GR is the most accurate theory of gravity we have currently.

Chronos

This may help http://math.ucr.edu/home/baez/physic...particles.html

Paulibus

I agree strongly. Physicists, when asked to explain what something IS, can only describe as best they can: what it does, how it works in relation to other stuff etc..... till the cows come home, if there is a strong need for clarity. Try describing what a bicycle IS, for practice!

For gravity, physicists have available for description the language of mathematics, including an esoteric kind of geometry-cum-tensor yak which so far provides the best predictive and quantitative description of this particular mystery. Backus should realise what she/he IS: an evolution-conditioned, hard-wired, all -talking, -writing and -describing species of African ape (great to BE one such).!

ImaLooser

The "why" game, known to every four year old.

As a question. Whatever the answer, ask "why?" Repeat until the adult says "Because I said so."

The why game seldom gets beyond five answers. Two is fairly typical.