a_vesper%Shasta@sarah.UUCP (02/29/84)
My first reaction to Steven Maurer's letter (SFL v 9 # 36)
was to send a brief note with my own comments on
possibility/impossiblity of FTL travel to the SFL
newsletter. My second reaction was a feeling that the
subject has been discussed enough for this year.
I eventually decided to go through some previous SFL issues
(volume 9 only 'cause that's what was on-line) and point out
all discussions of FTL, give a (very) brief summary and add
my comments after each. I searched for "FTL" so if there
was any discussion that did not use that abbreviation I did
not pick it up.
Mon, 16 Jan, # 12 : Ken Varnum <decvax!dartvax!kenv @ ucb-vax>
Does time slow down as you approach the speed of light (c)
and go backwards if you go faster than light?
The answer to the first half of the question is very well
explained in the next citation. The second half cannot be
answered at this time -- we just don't know because we don't
any experimental data.
Mon, 16 Jan, # 13 : Bruce Giles <decvax!duke!ucf-cs!giles @ ucb-vax>
An excellent discussion of special relativity, length
contraction and time dilation, but longer than I want to
include here.
Wed, 18 Jan, # 15 : Joe Buck <buck@nrl-css>
"Special relativity shows that if FTL travel is
possible, time travel (and causality violation) must
occur as well."
"Actually, relativity doesn't explicitly prohibit FTL
travel. It just shows that an object with mass can't
be accelerated continuously from a velocity below c to
one above c."
I believe that special (and general) relativity simply don't
say anything about FTL travel, but only STL travel. The
definitions that Einstein came up with for 'time' and
'simultaneity' are paired directly with relativity and the
STL universe. A new theory showing how FTL travel is
possible would have to redefine those terms, and probably
'cause' and 'effect' as well.
Einstein also showed that it takes more and
more energy to accelerate a body (with mass) closer and
closer to c and that it would take infinite energy to
accelerate a body TO c. Assuming that you must accelerate
from below c THROUGH c to above c gives you the impossibility
of FTL travel. (There is a discussion of Tachyons later in
this note.) As an aside, bodies without mass (e.g. photons)
always travel at c in a vacuum.
Sun, 22 Jan, # 17 : Jeff Duntemann <duntemann.wbst @ PARC-MAXC.ARPA>
Postulates a starship drive which accelerates all
particles within a given volume equally. "This violates
no physical laws that I know of."
With 2000 or 3000 G acceleration a trip to the nearer
stars becomes a matter of weeks or months rather than
centuries. (Personal time rather than universe time.)
I don't have my copy of *Have Space Suit, Will Travel* by
Robert A. Heinlein with me, but in that novel RAH shows that
a constant acceleration of less than 10 G is sufficient to
get to the nearer stars in a matter of 'weeks or months'.
2000 or 3000 G would probably get you there within seconds.
I can't do that kind of math in my head so I'll leave it as
an exercise for the reader.
Tue, 24 Jan, # 18 : Eric G. Stern
<hplabs!hao!seismo!philabs!sbcs!bnl!stern @ Ucb-Vax>
Eric comments that the starship drive which accelerates
all particles within a given volume equally requires
communicating a change in velocity instantly over a
non-zero distance, which is prohibited by special
relativity.
Oh well. TANSTAAFL.
Thu, 23 Feb, # 36 : Steven Maurer <sun!qubix!steven @ Ucb-Vax>
"Thus, though it is possible for "Psychism" to exist,
even "magic" (as long as it is in another universe), FTL
cannot." "Period."
Bunk. Why can't FTL exist in another universe? Call it
"magic" if you want. Why can't FTL exist in our universe?
It might, but we don't know how yet. Personally I don't
expect to see it possible in my lifetime, and maybe never
(although 'never' is a very strong word).
Hard science fiction often takes a theory just past where it
breaks down (such as relativity and 'c') and declares that
reality works differently from there. FTL is prime science
fiction material in this light.
Tue, 28 Feb, # 38 : Mike Gannis <offnet at LOGICON>
Mike compares Einsteinian relativity to Newtonian
physics: "Would you class as fantasy all stories
involving sub-c time dilation effects simply because
they aren't predicted by Newtonian physics?"
I agree. Newtonian physics cannot handle time dilation.
Einsteinian relativity cannot handle FTL. Both are 'true'
in that they are useful descriptions of the 'world' with
certain limitations.
I have not seen any mention of Tachyons in the recent past,
so I will bring up the subject myself. If you take
Einstein's theories and turn them around slightly, you have
a universe where all massive objects travel faster than c,
it takes energy to slow them down towards c and infinite
energy to slow them down to c. This universe is called a
Tachyon universe and the particles in it are Tachyons. This
gives rise to the following FTL drive principle: change
matter into tachyons going in the right direction, travel
the distance then change back into normal matter. In order
to do this, you need (1) the normal universe, (2) the
tachyon universe, (3) some way to convert between normal
matter and tachyons and (4) someplace to stand while doing
the conversion. (4) implies that the normal 'universe' and
the tachyon 'universe' are only subspaces of the 'real
universe'. The normal 'universe' would then not have to
obey conservation laws, which are tricky things to get
around when all that normal matter/energy disappears (and
reappears somewhere else -- presumably with different
potential energy).
Wormholes in space are also convenient FTL 'drives'.
Unfortunately, this also implies a space larger than the
'universe' within which the 'universe' is folded. And you
still have to do something about conservation. (Simply
saying that conservation doesn't hold is tacky and doesn't
help much anyway.)
Sorry for running on to such a length, but I hope I cleared
up some of the misconceptions. I will close with my
recollection of an old limerick:
There once was a woman named Bright,
Whose speed was far faster than light,
She set out one day,
In a relative way,
And came back the previous night.