Re: Misc Questions

From: Brian Tung (brian_at_isi.edu)
Date: 06/16/04 

Date: Wed, 16 Jun 2004 05:37:02 +0000 (UTC)

Vladimir Sacek wrote:
> Cousin Ricky, I asked a simple question: what is it in my writing that
> shows that I not just don't understand general relativity, but that -
> as you guys that "understand the basics" state - don't have a clue
> about it? None of you has yet put the finger on it. Brian wouldn't
> share his "basic understanding" with those less fortunate; you say
> everything is clear to you, but you can't really explain why and how.

I didn't say everything is clear to me. I said that I understand GR only
on a very superficial level. Quite different.

I didn't say that you don't have a clue. I said that your post indicated
that you don't understand general relativity. Quite different.

I never said that I wouldn't share my "basic understanding." In fact, I
have made available a lay explanation of what little I understand. Quite
different once again.

Please don't mischaracterize what I write.

Now, to the material in question. Yes, speeds are relative. If we see
the quasars as receding at speeds approaching that of light, then it's
also true that anyone there will see us receding from *them* at the same
speeds. Yet, we are not in any danger of suddenly "disintegrating" into
light. In fact, you cannot make anything at all disintegrate like that
merely by accelerating it to the speed of light, for the simple reason
that you cannot make anything with mass (like a galaxy) travel at the
speed of light. We'll never see any galaxy recede from us at the speed
of light (though they might be very close to the speed of light), nor
will they see us recede from them at that speed.

What's more, the galaxies are not plowing through space-time at anything
like relativistic speeds. Rather, the expansion of space-time is carrying
the galaxies away from each other.

Brian Tung <brian@isi.edu>
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