**Next message:**xgl: "Re: Flat universe == Infinite Universe?"**Previous message:**Fred C. Moulton: "Re: extropian sociality (was RE: Confronting The Singularity Conference)"**In reply to:**hal@finney.org: "Re: FTL transmission?"**Next in thread:**John Clark: "Re: FTL transmission?"**Reply:**John Clark: "Re: FTL transmission?"**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ]

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?

Don Klemencic

-----Original Message-----

From: owner-extropians@extropy.com [mailto:owner-extropians@extropy.com] On

Behalf Of hal@finney.org

Sent: Saturday, June 03, 2000 6:34 PM

To: extropians@extropy.com

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

ones.

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

moving.

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

stationary.

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

of light".

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.

Hal

**Next message:**xgl: "Re: Flat universe == Infinite Universe?"**Previous message:**Fred C. Moulton: "Re: extropian sociality (was RE: Confronting The Singularity Conference)"**In reply to:**hal@finney.org: "Re: FTL transmission?"**Next in thread:**John Clark: "Re: FTL transmission?"**Reply:**John Clark: "Re: FTL transmission?"**Messages sorted by:**[ date ] [ thread ] [ subject ] [ author ]

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