
We all know that radio waves propagate at a speed equal to that of light or "c"  approximately 300,000 km/sec or 186,100 miles/sec.
I once knew why this is so. I think it had something to do with what James Clerk Maxwell discovered i.e. for radio waves/light to propagate as they do, the speed must be 300,000 km/sec.
Can anyone explain the physics behind this important constant "c"?
Well, I'm not sure why the speed of light is what it is, but radio waves travel at light speed because light itself is a frequency of radio waves; they're the same thing.
Hi,
I beleave this universe is made up of only 2 things.
Matter and Energy and this C is constant that governes the relation between matter and energy
That is pretty standard physics so no problem.
What is gravity is your belief? A force? Where does it fit in the matterenergy universe?
chatrack wrote: 
I beleave this universe is made up of only 2 things.

Bikerman wrote:  What is gravity is your belief? A force? Where does it fit in the matterenergy universe? 
Well, one can hardly say the universe is 'made up of' gravity, so that's not a problem.
ocalhoun wrote:  chatrack wrote: 
I beleave this universe is made up of only 2 things.

Bikerman wrote:  What is gravity is your belief? A force? Where does it fit in the matterenergy universe? 
Well, one can hardly say the universe is 'made up of' gravity, so that's not a problem.  Well, yes it is. It is a pretty fundamental question  arguably THE fundamental question.
Bikerman wrote:  Well, yes it is. It is a pretty fundamental question  arguably THE fundamental question. 
A pretty fundamental question, yes. But how is it related to talking about what the universe is 'made up of'?
ocalhoun wrote:  Bikerman wrote:  Well, yes it is. It is a pretty fundamental question  arguably THE fundamental question. 
A pretty fundamental question, yes. But how is it related to talking about what the universe is 'made up of'? 
Well, if the universe is matter and energy and (as Einstein taught us) the two are really just ways of talking about the same overall concept) then the question is obviously  where did the energy come from?
If, on the other hand, gravity is regarded as opposite in sign to energy/mass then it all cancels to zero.
energy/mass = +ve quantity
gravity = ve quantity (equal and opposite to energy/mass)
therefore energy in universe is 0
Now, you might say, what a sweeping assumption to make. Not really.
I'll repeat an earlier thought experiment to illustrate.
Take a hollow shell of elastic material with radius r
We have gravity=+ve at distances >=r from the centre of the shell. This can be explained in GR as a distortion of the surrounding spacetime.
We have gravity = 0 at distances < r (the proof of this is nontrivial  Gauss Law  and is explained in more detail HERE
If you want the maths then:
OK. So now imagine we increase r to 2r. We do this by 'winching' the shell 'outwards'. This requires energy, obviously. So we put energy into the system and what do we get?
gravity at distances >= 2r = same as before (no change in mass)
gravity at distanced < 2r = 0 (see above)
So we have effectively reduced the total amount of gravity (because there is now a larger region of 'flat' spacetime inside the shell which has zero gravity) at the expense of some energy.
This tells us that gravity is proportional to negative energy which can be put as
G = k*e
(where G is gravity, e is energy and k is a constant)
Strictly speaking I should be talking about Gravitational Potential Enegy to make this more rigorous, because the above assumes that gravity and energy share the same units of measurement, but I've tried to keep it a simple explanation rather than a rigorous proof.
Bikerman wrote: 
Strictly speaking I should be talking about Gravitational Potential Enegy to make this more rigorous, 
So, why couldn't we just say it is (partly) made of the gravitational potential enegy, and skip the messiness of having to include gravity as one of the things the universe is made up of?
Well gravity is the one we know least about. We don't have a mechanism at the quantum level and that makes the particle guys twitchy, and our 'big' model (General Relativity) goes bonkers at the extremes (black holes) and requires a smooth spacetime, whereas any proper unified theory looks like it must be quantised. We know GR is 'wrong' at the extremes and we know QM works at the tiny level, but there is no evidence for the quantum physicists hypothetical gravity quantum  the graviton, and QM is hugely cumbersome at macro levels. Hence physics is stuck at the moment, waiting for someone to fill in the gap...
Gravitaional force and other fundamental forces are explained
on the basis of 'Exchange Particles'. In Nuclier forces , the binding
energy is explained as exchange of pai messons, i think
Just like that graviton, plays the role in Gravitation, but how...
Ill agree with the other fellow. The universe is made up of energy and matter, gravity is just a field caused by the bending of space time (got to love Einstein). But you are saying it is also something that makes up the universe because it is neither an energy or matter. Well take a look at the other force most commonly compared to gravity, the electrostatic force. It operates in much the same way that gravity works, and it would also pass the proofs that you just used.
So does that mean matter, energy AND gravity AND electrostatic makes up the universe?
Simply...no
You are right that we are stuck with a gap right now in the world of physics, but it doesn't mean we are not moving forward. And just because we can't explain the mechanism by which gravity works does not mean it is basic building block of the universe.
Although all of your proofs hold, and your knowledge of physics seems sound. Your argument makes no sense from an out side prospective. Can you please state your thesis more clearly.
P.S. I'm studying to be a theoretical physicist
Gravity is due to curvature of space time but getting hold of this idea is a bit complicated. Actually I am studying tensor which plays an important role while explaining Einstein relativity theory and its also very confusing.
BTW can anyone give me a site or ebook where I can get a good knowledge of Tensor from scratch?
