Questions about Physics, Biology and perspective

[Alex K]

That brings me to another question, actually.

If the universe is expanding, then how does this affect the value of "c" over time?  Do those kilometers themselves stretch out, meaning that light will still take the same time to travel, or does the distance the light have to travel actually increase while it's "in flight"?  I suppose it must be the latter, since light emitted 14 billion years ago has taken a long time to reach us on Earth, and at the Big Bang everything was packed into an infinitesimal volume.

I'm not 100% sure I understand how you mean it. Maybe it would be important to clearly define what we mean by speed of light. The best is to define it locally: You have a defined short ruler and a clock, both are calibrated by using some atomic process for example. You send a light signal along your ruler and measure the time, and divide. It is important that your apparatus is small enough that space is not noticeably bent along the ruler, and does not expand noticeably while the experiment is running. This is what is meant by local - you make the experiment arbitrarily small and quick to eliminate all curvature effects and get as a result the speed of light at that point.

This local speed of light apparently remains, for all we know, constant during cosmic expansion and is the same everywhere, whether you are orbiting a black hole or are in free space. It certainly does so in Einstein's description via General Relativity. What can happen though is that the distance the light travels in a year will be more than a light year once the light has arrived, because the distances it has already travelled will get stretched by cosmic expansion. This is why the radius of the visible universe is given as 46 billion light years, even though the light was only travelling for 13.8 billion years: The distance between us and the source has been stretched in the meantime by space itself expanding.

The other thing is-- if space is expanding uniformly, wouldn't the light transmitter, the light itself, and the receiving mechanism all be expanding identically, meaning that you'd "sense" the light as being the same frequency as when it left the emitter?  Why would there be any sense of relative change at all?

This is not a trivial question at all. The answer is well known, but it is a kind of subtle argument. I always knew that the size of matter etc. isn't affected by cosmic expansion, but it was only after I got my degree, when preparing for a public lecture, that I thought, wait a minute, do I understand this? and did the -admittedly short- calculation myself. When you look at the maths, you notice the following: If you use the appropriate definitions, the strength of the forces such as the strong force, weak force and electromagnetism as well as the masses of particles do not change with the expansion of space. It is those forces and masses which define the sizes of atoms and atomic bonds, and hence the sizes of stuff. If the atoms in matter weren't bound together by an unchanging electromagnetic force and also gravity, they would parttake in cosmic expansion. In fact, all matter does experience a minuscule tug from cosmic expansion trying to inflate it. But this force is so tiny that it only becomes important compared to electric and gravitational attraction at scales far beyond our galaxy.

I suppose that means that the red shift isn't a transformation but really is only a Doppler effect.  But would that mean that objects in the far reaches of the universe are actually traveling away from us at greater than the speed of light, or will it be kind of like an inverse Black Hole, where all very far objects appear to flatten into a tremendous sphere at massive distance?  Why isn't there a "wall" of super-low frequency light crushing us right now?

see my last post. The cosmic expansion is not sensibly described as stuff moving away at speed x.