FIRTH%TARTAN@CMU-CS-C.ARPA (01/02/84)
Just a minor nitpick: the speed of light is NOT the same on Pluto
as on Mercury, since it depends on the gravitational potential. It
is also not necessarily the same for moving observers in a gravitational
field, since their frames of reference might be stressed.
Now the real problem: if we can already DETECT a black hole at the centre
of the galaxy, then we have a lot less than 30,000 years to get out of here.
It is one thing for Beowulf Sheaffer to go by FTL drive to see the core,
and quite another for visible evidence to reach us at light speed. If we
suppose that fast particle radiation travels at upto 99% of the speed of
light, then it will start hitting us 300 years after we see the light from
matter being sucked into the hole.
How much radiation? How much will be emitted in the galactic plane, which
presumably is the plane of rotation of the hole (angular momentum being
conserved)? Do we panic now, or will it wait until next century?
Happy New Year.
PS - the giant spiders of Metebelis III get the crystal back, but the Queen
Spider (all praise to the Great One!) cannot stand the shock of being
so super-intelligent and explodes with lots of cheap special effects.
The idea of a spider spinning a web of brain matter may be original to
the episode, or may have been lifted from Ballard's The Voices of Time.
-------johnc@dartvax.UUCP (John Cabell) (01/05/84)
Your mention that the speed of light is different on Mars
is different on Mercury can't be right. The speed of light
is fixed, no matter where you are, isn't it?
--
From the Ever-Questioning Mind of
johnc
...!decvax!dartvax!johnc
:->rlw@wxlvax.UUCP (Richard L. Wexelblat) (01/05/84)
The speed of light is constant in a vacuum. ...leading to interesting paradoxes such as: A spaceship is leaving Earth at a speed of .5C and you shine a flashlight out of the forward porthole. What is the speed of the photons a)with respect to you, b)with respect to an observer on Earth. The answer is C to both a) and b), of course. --dick wexelblat (...decvax!ittvax!wxlvax!rlw)
jonab@sdcrdcf.UUCP (Jonathan Biggar) (01/05/84)
In article <15073@sri-arpa.UUCP> JAF%MIT-SPEECH@MIT-MC.ARPA writes: >From: Joseph A. Frisbie <JAF%MIT-SPEECH@MIT-MC.ARPA> > >The speed of light is rarely the same, it depends on the material it is >passing through. (Alot slower in dielectrics.) The density of the >vaccuum is probably greater closer to the sun. Also aren't there >gravitational effects, or do space and time change proportionally? Does this mean that we could collect more vaccuum closer to the sun? :-) -- Jon Biggar {allegra,burdvax,cbosgd,hplabs,ihnp4,sdccsu3,trw-unix}!sdcrdcf!jonab
friedman@uiucdcs.UUCP (friedman ) (01/07/84)
#R:sri-arpa:-1500700:uiucdcs:12500061:000:596 uiucdcs!friedman Jan 6 11:33:00 1984 Wait a minute. The speed of light in a vacuum is a constant for all oberservers in all frames of reference. As for the amount of time we have to escape radiation from the center of the galaxy: I don't remember how far away we are from the center, and therefore from that hypothetical black hole, but I'm under the impression it's a lot further than 300 light years. Even more fundamental, if there is dangerous radiation from that kind of cosmic source, it is unlikely to be different today, 300 years from today, or 30,000 years from today; all of those are small times on the cosmic scale.
johnc@dartvax.UUCP (John Cabell) (01/07/84)
>> Could we collect more vacuum nearer the sun?
I would think so. The sun heats up what particles there are
so they are moving faster, and are farther apart. Therefore
there is 'more of a vacuum'.
--johnc
--
From the Ever-Questioning Mind of
johnc
...!decvax!dartvax!johnc
:->richard@sequent.UUCP (01/09/84)
Uh...sorry. Vacuums are harder farther away from the sun. The best place to go for absolutely NO pollution would be outside of the galaxy - preferably outside of our universe. The sun is spewing out material constantly - in general, vacuums are worse close to gravitational bodies. See net.astro or .physics for details. A decent book that incorporated this fact is *TAU ZERO* by (i think) Poul Anderson. His science in this one is pretty hard, although the ending is a little far-fetched. ...!sequent!richard the rider in black
wetcw@pyuxa.UUCP (T C Wheeler) (01/09/84)
Just wondering, how do "collect" a vacuum? Perhaps you mean "uncollect"? To collect something, there has to be something to collect, right? Then, it must follow that to collect nothing, nothing can not be collected, thus, you can't collect a vacuum.:-). Puzzeled by it all --T. C. Wheeler
riber@uicsl.UUCP (01/10/84)
#R:sri-arpa:-1507300:uicsl:10700073:000:128 uicsl!riber Jan 9 09:21:00 1984 can you link this subject to science fiction or are you lost. please use the correct notes group for this discussion. riber
giles@ucf-cs.UUCP (Bruce Giles) (01/11/84)
1: Even more to the point with the radiation question -- There should
be no difference in radiation in comparison with 300 years *ago*,
3000 years *ago*, etc. The fact that we are still here tends to
strongly support the view that we will still be here tomorrow. (A
related question was recently discussed on net.math concerning
the success of the MAD doctrine: the implication was that since
we have survived 38 years of mutual possesion of nuclear devices,
the odds are no greater than 1/38 that we will not survive next
year, all things being equal.)
2: The time compression due to gravitation effects can be determined
using general relativity; however the effects are negligible for most
reasonable problems. One thing which is not as negligible, however,
is orbital precession due to (a) the presence of mass, and (b) the
rotation of said mass. In fact, it was due to an *anomoly* in the
calculated precession of Mercury's orbit that general relativity
was developed. It now appears that this anomolous precession can
be explained by a better model of the structure of the sun, leaving
very serious questions about general relativity. BUT -- special
relativiy is still on extremely firm theoretical ground, and in
the question of which is `more accurate', I suspect that sr will
come out ahead. (alas).
3: If you want to be picky, every single science fiction book which
uses time-warps, hyperdrive, et nauseam is related to this discussion.
I may be a personality defect to some individuals on the net, but I
can not seriously consider any book/story/idea which is not at the
least possible in my eyes. As a result, I *loath* lord of the rings,
etc.
Some science fiction storys/books/... which would be affected by
this physics phenomenum are:
*The Forever War* by J. Haldeman -- uses black holes for
transportation, time compression
*The McAndrew Chronicles* by ? -- deals heavily with special
and general relativity, ECD and QED.
The Known Space series by Larry Niven -- The most visible example
is the calculation (in gr) that
Shaffer's ship will leave the
black hole with a sizable spin
in *Neutron Star*.
If it is insisted that this discussion refer to science fiction
stories, the McAndrew Chronicles alone contain enough material to
make this net look like net.physics for a few months (:-}).
Bruce Giles
---------------------------------------------
UUCP: decvax!ucf-cs!giles
cs-net: giles@ucf
ARPA: giles.ucf-cs@Rand-Relay
Snail: University of Central Florida
Dept of Math, POB 26000
Orlando Fl 32816
---------------------------------------------JAF%MIT-SPEECH@MIT-MC.ARPA (01/11/84)
From: Joseph A. Frisbie <JAF%MIT-SPEECH@MIT-MC.ARPA> The speed of light is rarely the same, it depends on the material it is passing through. (Alot slower in dielectrics.) The density of the vaccuum is probably greater closer to the sun. Also aren't there gravitational effects, or do space and time change proportionally? Joe -------
ab3@pucc-h (Darth Wombat) (01/11/84)
I would think so. The sun heats up what particles there are
so they are moving faster, and are farther apart. Therefore
there is 'more of a vacuum'.
--dartvax!johnc
Sorry, but incorrect for a number of reasons:
1. The sun emits particles; assuming that this emission is
roughly isotropic means that the density of emitted particles is
roughly inversely proportional to radial distance from the sun to at
least the second power.
2. Directly addressing your point -- the "harder vacuum" is one
with fewer particles per volume; not one with "faster particles per volume"
or "farther apart particles per volume". I.e. the particle density will
stay constant for any macroscopic volume since any {quickly} exiting
particle will probably be replaced by a {quickly} entering particle.
--
"Go ahead...make my day."
Darth Wombat
{ allegra, decvax, ihnp4, harpo, seismo, teklabs, ucbvax } !pur-ee!rskkcarroll@utzoo.UUCP (Kieran A. Carroll) (01/11/84)
* The McAndrew Chronicles is a collection of stories by Charles Sheffield (three cheers!), which have appeared in various SF magazines over the last few years. A personal note: there are several scientists presently practicing science-fiction writing. Charles Sheffield has mastered it; he need not practice any more (although I sure hope that he does!). -Kieran A. Carroll ...decvax!utzoo!kcarroll
wetcw@pyuxa.UUCP (T C Wheeler) (01/12/84)
Come now gentlefolk, "density" of a vacuum?