# Can Spacetime Curvature change c ?

1. Apr 1, 2004

### Antonio Lao

I am not sure.

2. Apr 1, 2004

### Integral

Staff Emeritus
No, c, the SPEED of light does not change with the curvature of space. The VELOCITY of light , however, can change.

Edit:
Keep in mind that we live in a curved region of space, yet we measure a constant c.

3. Apr 1, 2004

Integral,

Thanks.

4. Apr 1, 2004

### Hurkyl

Staff Emeritus
Also, keep in mind that our choice of (inertial) coordinates can influence our observations of events not happing right next to us. In most coordinate systems, the coordinate velocity (dx/dt, dy/dt, dz/dt) for light does not need to have magnitude c at distant points. One can interpret this as saying that the geometry of space distorts our observation of distant events.

Though, if you choose an (inertial) coordinate chart centered at that distant point, the coordinate speed of light there would, in fact, be c.

5. Apr 1, 2004

### Antonio Lao

Am I right to say that an inertial frame is just another way of saying a rest frame of coordinate? c is c only if it is measured in a local frame of reference that is at rest.

6. Apr 1, 2004

### Hurkyl

Staff Emeritus
I'm not the person to turn for GR semantics. But yes, what I said is an inertial coordinate chart is one that would be appropriate for the rest frame of an inertial observer.

7. Apr 1, 2004

### p-brane

So, theoretically, if I was going the speed of light, light would be standing still within the parameters of general relativity and according to my personal inertial frame ? (sorry, slightly off topic)

8. Apr 1, 2004

### Antonio Lao

If we accept the fact that we get c only in a rest frame and that c is measured equally at any rest frame location in the universe, then it can be said that as a whole, the universe is at rest but the things inside it are not at rest. In other words, the total linear momentum of the universe is zero.

Last edited: Apr 1, 2004
9. Apr 2, 2004

### Organic

Then C constant means that we are talking about a deep symmetry of our universe, where each non-zero measurement can be naturalized by its opposite.

This is the macro picture, but from the QM micro picture we have learned that uncertainty is also a fundamental property of our universe.

String theory tries to connect between the macro picture and the micro picture by ignoring the uncertainty, but I think this is a mistake, because in my opinion, uncertainty and redundancy are fundamental properties of any universe that includes creatures like us, who can ask questions about it.

C is the signature of stability of where Plank h is the signature of non-stability.

Last edited: Apr 2, 2004
10. Apr 2, 2004

### Antonio Lao

We know that many researchers are still working on how to combine the micro and the macro into something that is in between. I can call it midcro (middle world). In a sense, human beings are the middle point between the microworld and the macroworld.
Is this what is called the anthropic cosmological principle?

There are many other physical constants of nature besides c that no one knows why they have their respective empirical values. The anthropic principle indicates that these constants are what they are so that human consciousness can exist.

11. Apr 2, 2004

### Organic

I think that the main point here is that our universe is based on the ability to associate between opposite properties, where the results of these associations is any thing that survives mutual destruction.

Our cognition's abilities are first tuned to self reservation, and the meaning of this is to define non-destructive ways to survive and flourish.