I wonder if the principle of relativity is not weakened or compromised by
the big bang theory. Doesn't the center-of-mass of the big bang, i.e., the
center of mass of the cosmos, define a privileged frame of reference?
Doesn't motion in any other frame of reference produce a blue shift in the
2.7 K black body background radiation in the direction of motion relative to
center-of-mass and a red shift in the opposite direction?
From: email@example.com [mailto:firstname.lastname@example.org] On
Behalf Of email@example.com
Sent: Saturday, June 03, 2000 6:34 PM
Subject: Re: FTL transmission?
The theory of relativity did not start with the assumption that FTL
travel was impossible. Rather, it started with a much simpler assumption,
called the "principle of relativity" (which is not the same as the theory
of relativity). This can be stated somewhat informally as:
The laws of physics are the same for moving observers as for stationary
This principle is based on observations: in a smoothly moving frame of
reference, there is no self-contained measurement you can do which will
have a different result than if you were moving at a different speed.
You can't reach out and "feel space sliding by" to tell that you are
It follows from this that actually there is no such thing as a
"stationary" observer; that is, motion is all relative. If one person
is moving with respect to another, each one has an equal claim to being
One of the things that has been found is that empty space has certain
magnetic and electrical properties, which you can measure. And further
it turns out that it is possible to have waves travel through empty
space which are made purely of electricity and magnetism. These waves
are the familiar electromagnetic radiation which we observe as light,
radio, and so on.
The speed of these waves depends on the electrical and magnetic properties
of space. Based on the principle of relativity, we can say that both
stationary and moving observers will measure these values to be the same.
It follows that all observers will see electromagnetic waves travel at
the same speed. This speed is abbreviated "c", and is called "the speed
Independently, puzzling experimental results were obtained which also
pointed to the speed of light being the same for all moving frames of
reference. This was the Michelson-Morley experiment which measured
the speed of light relative to the earth's motion around the sun.
No difference was found in the speed regardless of which direction the
earth is moving.
This result, by itself, is enough to begin to capture some of the
paradoxes of relativity. How can two people in motion relative to each
other both measure the speed of a given beam of light to be the same?
Our intuitive understanding would say that one of them would see the
light to be moving faster than the other. Yet experiments and argument
imply that this does not happen.
Einstein's theory of relativity explores the implications of this effect
in detail. It is from this theory that we learn that measurements of
time and distance are different for observers in motion. This should
not surprise us, because speed is distance divided by time, and we
already have a paradox when moving observers measure the same speed,
which should be impossible. So the fact that they measure distances and
times differently almost goes without saying once we hit this paradox.
Einstein just worked out the math.
Some people have suggested that Einstein's equations wouldn't work for
observers going faster than light. After all, we have never done any
experiments in that case. Maybe something else happens.
This is conceivable, but not that germane. In the experiment which led
to this discussion, no observers were going faster than light. Rather,
we had a phenomenon which gave the impression (apparently illusorily)
that a pulse was travelling faster than light. So all we really need
to know is whether Einstein's equations have been tested or would be
applicable to physical phenomena which go faster than light.
And in fact, the way Einstein's equations work, FTL communication can
be analyzed in the same way as any other set of events which occur at
close to the same time. You don't need exotic equipment. The Mars
Global Surveyor camera takes a picture at the same moment that something
happens in the lab here on earth. It's going to take an hour for the
picture to get back, but Einstein's equations tell us how to analyze the
simultaneous events in terms of a moving observer. These are exactly
the same kinds of equations which would be used for FTL communications.
So there is no reason to think that FTL communications would be a new
exotic regime where Einstein's equations don't apply. The basic concept
of simultaneous or near-simultaneous events is extremely ordinary and
is handled perfectly well by the theory of relativity.
Summing up, the theory of relativity is based on a very general
philosophical principle, that there is no such thing as ABSOLUTE
SPACE where you can reach out and "feel" whether you are moving or not.
It is further supported by the observation of the constancy of the speed
of light. And in the years since, it has made many other predictions
which have been borne out. All of this gives us confidence in the
accuracy of the theory. Based on this experience, we can predict that
FTL communications would allow for backwards-in-time communications,
raising severe problems of causality and logical consistency. It is
therefore very unlikely that FTL communications are possible.
This archive was generated by hypermail 2b29 : Thu Jul 27 2000 - 14:12:27 MDT