Re: Time Machines

Gabriele Betti (
Mon, 23 Aug 1999 13:26:51 +0200

Could you translate the example of the laser in the sphere(2 light years....) in a math formula?

At 22.08 22/08/99 -0700, you wrote:
>On Sun, Aug 22, 1999 at 11:04:31AM -0400, John Clark wrote:
>> In looking over the Extropian archives I noticed that the subject of
time machines
>> and faster than light travel came up on the list about a year and a half
ago, I didn't
>> have time
>[.... snip]
>> A less spooky example could be found in the idea of Phase Speed. I'm
>> in the center of a huge hollow sphere 2 light years in diameter, I've been
>> there for a long time and I'm holding a powerful LASER that makes a spot of
>> light on the distant wall of the sphere one light year away. Suddenly,
>> holding the LASER and in the space of one second I make a complete 360
>> degree turn. Exactly 2 years later an observer standing at the same place
>> would see the spot move much faster than light, it would travel the entire
>> circumference of the sphere, 2PI or 6.28 light years in only one second.
>> No photon moved faster than light however, and no energy or information
>> between any two points traveled faster than light. A photon of light moves
>> at light speed and carries energy and information, a spot of light can move
>> at any speed but carries neither energy nor information.
>Nice example. To those who are confused and are inevitably going to
>ask for an explanation (I peeked into the future), try thinking
>about the path in time and space of the photons being spewed out
>from the laser. Think of them as rubber bullets that bounce off the
>inner surface of the sphere and into your eye.
>I agree that phase speed (which is unobservable directly) can
>"travel" at >c, but I don't see what that has to do with the example.
>But it doesn't matter.
>[... snip]
>> nature is totalitarian, if it's not forbidden then it's mandatory.
>> What about the logical paradoxes that would result from communicating with
>> the past, wouldn't that be enough to rule out Tachyons? It would if anybody
>> saw them, but suppose nature rubbed out any witnesses to her crime and
>> brought a universe to an end that was about to see a paradox.
>> Damn, I just knocked my coffee cup off the table, what a mess! I'm
really not
>> in the mood to clean it up, instead I'll use my Gateway 14,400 Tachyon
>> and send myself some E mail 2 minutes ago. I'll just hit the send key and
>> .....brought a universe to an end that was about to see a paradox.
Pardon me,
>> I just got some E mail from John, let's see what it says " Dear John: Be
>> careful with that coffee cup near your elbow, you're about to knock it
>> Wow, John is right, that cup is dangerously near the edge, I'll put it in a
>> safe place. It was nice of John to warn me about it, it's too bad that
>> oblivion for him and his entire universe but that's life, nature just will
>> not allow anybody to observe a paradox.
>> I know what you're thinking, how could John be so stupid, he must be
>> completely out of his mind, why else would he deliberately buy an obsolete
>> 14,400 Tachyon modem? Well, call me cheap if you want but I still think the
>> 28,800 model is too expensive, besides I have it on very good authority

>> Gateway will drop the price next year.
>> John K Clark
>[... snip]
>Don't worry, it's worse; there are universes in which John is using
>an Amiga.
>That is to say, in the many-worlds interpretation, the idea of time
>travel is non-paradoxical, since you really travel to an alternate
>universe what is similiar in most, but not all, aspects from the
>one you came from, and don't cause any paradoxes.
>See _The Fabric of Reality_. David Deustch. the chapter "Time, the
>first quantum concept". He explains it better than I can.
>Or his Scientific American article. (I don't remember "when".)
>[fyi, Gateway bought the rights to whatever is left of the Amiga
> *** California School Book Depository and ****
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