brad@looking.UUCP (Brad Templeton) (08/12/85)
Everybody goes on and on about how if you time travel, you should end up way out in space because the Earth is whizzing around the sun. Not quite true. Aside from the rotation of the Earth about its axis, the planet is in an inertial frame. To suggest a time traveller would appear where the Earth "was" implies some sort of absolute frame that the planet moves in. So in theory, if you come back at the same siderial time of day that you left, you would arrive at the same place. Of course, it's probably true that photon pressure and solar wind make the orbit of the Earth deviate slightly from an inertial frame. Does anybody know by how much? A time travel story where they claim they can only arrive at the same spot if they pick the exact time of day - that would impress me. -- Brad Templeton, Looking Glass Software Ltd. - Waterloo, Ontario 519/884-7473
csdf@mit-vax.UUCP (Charles Forsythe) (08/15/85)
In article <323@looking.UUCP> brad@looking.UUCP (Brad Templeton) writes: >Everybody goes on and on about how if you time travel, you should end >up way out in space because the Earth is whizzing around the sun. > >Not quite true. Aside from the rotation of the Earth about its axis, >the planet is in an inertial frame. To suggest a time traveler would >appear where the Earth "was" implies some sort of absolute frame that >the planet moves in. Nice try Brad -- but wrong. The earth orbits the Sun, the solar system orbits the center of the Milky Way Galaxy, and the Milky Way galaxy is accelerating slowly towards the center of the universe (but moving away). The Earth is NOT an inertial frame at all. -- Charles Forsythe CSDF@MIT-VAX "I was going to say something really profound, but I forgot what it was." -Rev. Wang Zeep
lauren@vortex.UUCP (Lauren Weinstein) (08/16/85)
The time machine that I built some years ago indeed used the current inertial frame reference, so there was no problem with finding oneself out in space. However, I also found that it was real easy to accidently muck around with history, and after discovering that it was impossible to put things back properly I gave up on time travel, came back to the present, and have tried my damndest to get used to the way things are "now." Maybe I'll have better luck with the Mach 2 matter transmitter. The Mach 1 was, uh, sort of "buggie." I should have kept a No-Pest-Strip in the lab. Oh well, live and learn. --Lauren--
petrick@lll-crg.ARPA (Jim Petrick) (08/16/85)
>>Everybody goes on and on about how if you time travel, you should end >>up way out in space because the Earth is whizzing around the sun. > >Nice try Brad -- but wrong. The earth orbits the Sun, the solar system >[rotates] (etc.) [a few lines removed from the middle] What's the problem? If someone was smart enough to build a time machine in the first place, couldn't they also think of compensating for these rotations in some manner? I know it would be nearly impossible to determine all the effects of different frames of reference, but then I'd think that the time travel aspect would be a much tougher nut to crack. Besides, he could experiment to determine these rotational (etc) effects. This discussion reminds me of an Isaac Asimov story about two scientists; one a slow and cautious thinker, the other a quick, jump-to-conclusions type. The two are jealous rivals out to outdo each other. The quick one invents a device for nullifying gravity, and to show up his rival places the device on the center of a pool table over a hole cut in the surface. To embarass his rival, the quick guy invites the slow guy to demonstrate what a great invention he has by shooting a pool ball across the hole in the table (and through the null-gravity field). The slow guy thinks a bit, then makes a bank shot so the ball is headed directly at the fast guy as it enters the field. There is a flash, and the quick guy has a hole punched through him by the ball (all gravity nullified, it was not accellerated along with everything else in our frame of reference, and stayed put while the rest of the world whooshed by). Two questions: Does anyone remember the title of this story? How could the slow guy predict which way the ball accelerated? Jim Petrick (petrick@lll-crg.ARPA)
throopw@rtp47.UUCP (Wayne Throop) (08/16/85)
> From: steve@sdcrdcf.UUCP (Steve Holtsberg) > I think you're dead wrong. Time and space are two different dimensions. > If you travel through time, you SHOULD end up in exactly the same spot > you were in "before" you left. Exactly so. But most time-travel scenarios have you ending up in the spot where the earth happens to be when you arive, not where the earth was when you left. (However, note that "time and space are two different dimensions" in about the same way that "front-back and left-right are two different dimensions". That is, there is no unique direction or dimension that is "most timelike". There are simply more restrictions on interchanging time-like and space-like "dimensions", but these restrictions do not prevent this mixing totally.) > Aside from the rotation of the Earth about its axis, the planet is in > an inertial frame. > Brad Templeton, Looking Glass Software Ltd. - Waterloo, Ontario 519/884-7473 No, it isn't. It is accelerated (around the sun, around the galaxy, etc.) There are plausible explainations of why a time-traveler "should" end up in the "same" spot relative to the surface of the earth, and other explainations as to why a time-traveler "should" end up in the same spot relative to some inertial frame or other (and hence "out in space somewhere"). Neither of these explainations are easy to follow, nor are either of them very convincing. Therefore, I expect time-travelers to do whatever the scriptwriter finds convenient. -- Wayne Throop at Data General, RTP, NC <the-known-world>!mcnc!rti-sel!rtp47!throopw
peter@baylor.UUCP (Peter da Silva) (08/17/85)
> Nice try Brad -- but wrong. The earth orbits the Sun, the solar system > orbits the center of the Milky Way Galaxy, and the Milky Way galaxy is > accelerating slowly towards the center of the universe (but moving > away). The Earth is NOT an inertial frame at all. "center of the universe"? First I heard that the universe has a center. -- Peter da Silva (the mad Australian werewolf) UUCP: ...!shell!neuro1!{hyd-ptd,baylor,datafac}!peter MCI: PDASILVA; CIS: 70216,1076
peter@baylor.UUCP (Peter da Silva) (08/18/85)
> through him by the ball (all gravity nullified, it was not accellerated > along with everything else in our frame of reference, and stayed put while > the rest of the world whooshed by). It was accelerated because it was a massless particle and had to travel at 'C', not because it was suddenly "left behind as the earth moved". > Two questions: Does anyone remember the title of this story? Nope. > How could the slow guy predict which way the ball > accelerated? Yeh, he figured it would keep going in the same direction on the absence of other forces. A perhaps unwarranted generalisation of Neton, but what the hell. -- Peter da Silva (the mad Australian werewolf) UUCP: ...!shell!neuro1!{hyd-ptd,baylor,datafac}!peter MCI: PDASILVA; CIS: 70216,1076
sean@ukma.UUCP (Sean Casey) (08/19/85)
In article <790@lll-crg.ARPA> petrick@lll-crg.UUCP (Jim petrick) writes: >This discussion reminds me of an Isaac Asimov story about two scientists; >one a slow and cautious thinker, the other a quick, jump-to-conclusions >type. The two are jealous rivals out to outdo each other. The quick one >invents a device for nullifying gravity, and to show up his rival places >the device on the center of a pool table over a hole cut in the surface. >To embarass his rival, the quick guy invites the slow guy to demonstrate >what a great invention he has by shooting a pool ball across the hole in >the table (and through the null-gravity field). The slow guy thinks a bit, >then makes a bank shot so the ball is headed directly at the fast guy as it >enters the field. There is a flash, and the quick guy has a hole punched >through him by the ball (all gravity nullified, it was not accellerated >along with everything else in our frame of reference, and stayed put while >the rest of the world whooshed by). That is ludicrous. The world would whoosh by only if the ball were under a force that would cause it to de-accelerate. If an antigrav field were maintained upon the ball, it would eventually leave the earth by centrifugal force, but not very quickly. For what you decribed to happen, the device would not only have to nullify gravity, but also place the ball in some relative movement such that the earth seemed to be whooshing by. -- - Sean Casey UUCP: sean@ukma.UUCP or - Department of Mathematics {cbosgd,anlams,hasmed}!ukma!sean - University of Kentucky ARPA: ukma!sean@ANL-MCS.ARPA
bch@mcnc.UUCP (Byron Howes) (08/20/85)
In article <744@vortex.UUCP> lauren@vortex.UUCP (Lauren Weinstein) writes: >The time machine that I built some years ago indeed used the >current inertial frame reference, so there was no problem with finding >oneself out in space. However, I also found that it was real >easy to accidently muck around with history, and after discovering >that it was impossible to put things back properly I gave up on >time travel, came back to the present, and have tried my damndest >to get used to the way things are "now." So *that's* what happened to usenet, and that bizarre artificial intel- ligence project at ucla... -- Byron C. Howes ...!{decvax,akgua}!mcnc!ecsvax!bch
lsr@apple.UUCP (Larry Rosenstein) (08/20/85)
In article <790@lll-crg.ARPA> petrick@lll-crg.UUCP (Jim petrick) writes: >..... > >This discussion reminds me of an Isaac Asimov story about two scientists; >one a slow and cautious thinker, the other a quick, jump-to-conclusions >type. >..... There is a flash, and the quick guy has a hole punched >through him by the ball (all gravity nullified, it was not accellerated >along with everything else in our frame of reference, and stayed put while >the rest of the world whooshed by). > I don't think that is the right explanation (at least not the explanation given in the story). When the gravity was nullified the ball became massless. Massless things (eg., photons) travel at the speed of light, accounting for the ball's velocity. -- Larry Rosenstein Apple Computer UUCP: {nsc, dual, voder, ios, mtxinu}!apple!lsr CSNET: lsr@Apple.CSNET
davew@shark.UUCP (Dave Williams) (08/20/85)
In article <744@vortex.UUCP> lauren@vortex.UUCP (Lauren Weinstein) writes: >The time machine that I built some years ago indeed used the >current inertial frame reference, so there was no problem with finding >oneself out in space................. > >--Lauren-- Lauren isn't telling all the story of why he stopped teleporting himself back in time. Lauren's lab is in Culver City, Cal. Have you ever wondered what that place was like 100 or 200 years ago? Let alone last week. -- Dave Williams Tektronix, Inc. Graphic Workstations Division "The 6000 Family" "The workstations that made Wilsonville famous."
zeke@dartvax.UUCP (Edward M. Zebrowski) (08/21/85)
In article <438@baylor.UUCP> peter@baylor.UUCP (Peter da Silva) writes: > >"center of the universe"? First I heard that the universe has a center. >-- > Peter da Silva (the mad Australian werewolf) Why Lord have mercy Peter, where have you been? zeke@dartvax.UUCP
lauren@vortex.UUCP (Lauren Weinstein) (08/21/85)
Actually, Vortex is in Los Angeles proper, not in Culver City... but there admittedly wasn't much here 200 years ago. The reason for my lack of photo on my Unix/World column is obvious--it's to avoid the spectre of mobs of autograph seekers whenever I'm on the street. (Uh huh). --Lauren--
pamp@bcsaic.UUCP (pam pincha) (08/21/85)
In article <2063@ukma.UUCP> sean@ukma.UUCP (Sean Casey) writes: >In article <790@lll-crg.ARPA> petrick@lll-crg.UUCP (Jim petrick) writes: >>This discussion reminds me of an Isaac Asimov story about two scientists; >>one a slow and cautious thinker, the other a quick, jump-to-conclusions >>type. The two are jealous rivals out to outdo each other. The quick one >>invents a device for nullifying gravity, and to show up his rival places >>the device on the center of a pool table over a hole cut in the surface. >>To embarass his rival, the quick guy invites the slow guy to demonstrate >>what a great invention he has by shooting a pool ball across the hole in >>the table (and through the null-gravity field). The slow guy thinks a bit, >>then makes a bank shot so the ball is headed directly at the fast guy as it >>enters the field. There is a flash, and the quick guy has a hole punched >>through him by the ball (all gravity nullified, it was not accellerated >>along with everything else in our frame of reference, and stayed put while >>the rest of the world whooshed by). > >That is ludicrous. The world would whoosh by only if the ball were >under a force that would cause it to de-accelerate. If an antigrav >field were maintained upon the ball, it would eventually leave the >earth by centrifugal force, but not very quickly. > >For what you decribed to happen, the device would not only have to >nullify gravity, but also place the ball in some relative movement such >that the earth seemed to be whooshing by. >- Sean Casey UUCP: sean@ukma.UUCP or >- Department of Mathematics {cbosgd,anlams,hasmed}!ukma!sean >- University of Kentucky ARPA: ukma!sean@ANL-MCS.ARPA I suggest you send your comments to the "good Doctor" and see what he has to come up with. He enjoys matching wits and formulas given half the chance. (He also is a bit of a ham, and loves attention and mail.) You can send him a note thru his Sci-Fi magazine address.
csdf@mit-vax.UUCP (Charles Forsythe) (08/22/85)
In article <20944@apple.UUCP> lsr@apple.UUCP (Larry Rosenstein) writes: >I don't think that is the right explanation (at least not the >explanation given in the story). When the gravity was nullified the >ball became massless. Massless things (eg., photons) travel at the >speed of light, accounting for the ball's velocity. This has to be the dumbest thing I've ever heard. MASS IS INDEPENDANT OF GRAVITY! Massless things (eg nutrinos) do not travel the speed of light most of the time, and when they do, it's ONLY IN A VACUUM! Good lord, didn't you go to highschool? Anyway, I'm routing this to net.bizarre, because it no longer belongs in net.movies. F=Ma, Larry. -- Charles Forsythe CSDF@MIT-VAX "We pray to Fred for the Hopelessly Normal Have they not suffered enough?" from _The_Nth_Psalm_ in _The_Book_of_Fred_
m1b@rayssd.UUCP (M. Joseph Barone) (08/29/85)
When an airliner travels from the East Coast to the West Coast,
no one is amazed that it travels along an arc of a circle rather than
tangent to one. When traveling through any of the space dimensions,
gravity has an effect on the moving object. In fact, traveling for-
ward in time is also affected by gravity. A stationary time machine
should glue the traveler to the exact location on Earth no matter how
far back or forward in time he goes.
Joe Barone, {allegra, decvax!brunix, linus, ccice5}!rayssd!m1b
Raytheon Co, Submarine Signal Div., Box 330, Portsmouth, RI 02871jtb@kitc.UUCP (John Burgess) (09/06/85)
In article <1016@rayssd.UUCP> m1b@rayssd.UUCP (M. Joseph Barone) writes: > .... A stationary time machine >should glue the traveler to the exact location on Earth no matter how >far back or forward in time he goes. That assumes that when travelling through the so-called fourth dimension one still exists in the normal 3 dimensions! It doesn't work that way! In fact, if it did, as soon as something else was put in "that exact spot" the time machine would run into it! (No two objects can occupy the same space AT THE SAME TIME!) John Burgess -- John Burgess ATT-IS Labs, So. Plainfield NJ (HP 1C-221) {most Action Central sites}!kitc!jtb (201) 561-7100 x2481 (8-259-2481)
sas@leadsv.UUCP (Scott Stewart) (09/13/85)
In article <1016@rayssd.UUCP>, m1b@rayssd.UUCP (M. Joseph Barone) writes: > > When an airliner travels from the East Coast to the West Coast, > no one is amazed that it travels along an arc of a circle rather than > tangent to one. When traveling through any of the space dimensions, > gravity has an effect on the moving object. In fact, traveling for- > ward in time is also affected by gravity. A stationary time machine > should glue the traveler to the exact location on Earth no matter how > far back or forward in time he goes. > > Joe Barone, {allegra, decvax!brunix, linus, ccice5}!rayssd!m1b > Raytheon Co, Submarine Signal Div., Box 330, Portsmouth, RI 02871 According to the Good Doctor, Isaac Asimov, in an article in a science fiction movie book (I believe the title was something like "Science in Science Fiction", but I'm not sure if this was the title of the book or article) Joe statement is incorrect. To travel in time, you must travel in space as well to end up in the same relative position as when you left. Since the Earth moves around the sun, the sun around Milky Way, and the Milkey Way around the universe, if you go back in time, the earth is no longer in the same position as it was when you left. Most time travel stories show the character moving only through the time dimension, and he would thus emerge again in the middle of space. Gravity would have no effect on time travel, since time is a dimension not effected by gravity (I.E. An Earth hour is the same length on Earth or Jupiter.) Traveling through time is not the same as traveling through the other 3 dimensions in which gravity would effect your ability to move through them. For a time machine to travel in time and emerge at the same location on Earth, it would have to be able to accurately calculate the angular displacement of the Earth, Sun, and Milky Way, or be pretty darn lucky. " I met him in swamp down on Dagobah where the waters always bubbling like a giant carbonated soda, S-O-D-A, Soda I saw him sitting there on a log and I asked him his name, and in a raspy voice he said Yoda, Y-O-D-A, Yoda, Yo-Yo-Yo-Yoda" Scott A. Stewart LMSC
ewa@sdcc3.UUCP (Eric Anderson) (09/15/85)
In article <1016@rayssd.UUCP> m1b@rayssd.UUCP (M. Joseph Barone) writes: > .... A stationary time machine >should glue the traveler to the exact location on Earth no matter how >far back or forward in time he goes. Consider: The earth rotates around it's axis at 1000 mph at the equator, around the sun at around 50,000 mph, and the sun rotates around the center of the milky way at ?? mph (anyone care to compute that?) If a time machine put you back even one hour at the exact same spot, you would be more than 51,000 miles from the earth (which would go whizzing past/through you one hour later) Eric Anderson, UC San Diego {elsewhere}!ihnp4!ucbvax!sdcsvax!sdcc3!ewa
scs@wucs.UUCP (Steve Swope) (09/19/85)
In article <2997@sdcc3.UUCP>, ewa@sdcc3.UUCP (Eric Anderson) writes: > In article <1016@rayssd.UUCP> m1b@rayssd.UUCP (M. Joseph Barone) writes: > > .... A stationary time machine > >should glue the traveler to the exact location on Earth no matter how > >far back or forward in time he goes. > > Consider: The earth rotates around it's axis at 1000 mph at the equator, > around the sun at around 50,000 mph, and the sun rotates around the center > of the milky way at ?? mph (anyone care to compute that?) > > If a time machine put you back even one hour at the exact same spot, you > would be more than 51,000 miles from the earth (which would go whizzing > past/through you one hour later) > Anyone clever enough to build a time machine in the first place is clever enough to account for the displacement. Likely, there would be a subsystem which would allow the pilot/operator to lock the machine's position relative to some object (e.g.; the local planet). Alternatively, the travel might occur in n-space (n>4), so that you would disappear at one place/time and reappear at another. By analogy, consider lifting the tip of a pencil from one place on a sheet of paper and moving it to another. Steve Swope (aka scs@wucs.UUCP) "Brigadier, A straight line may be the shortest path between two points, but it is by no means the most interesting!"
bl@hplabsb.UUCP (09/24/85)
> Gravity would have no effect on time travel, since time is a dimension > not effected by gravity (I.E. An Earth hour is the same length on Earth > or Jupiter.) Traveling through time is not the same as traveling through > the other 3 dimensions in which gravity would effect your ability to > move through them. Wrong! Gravity affects time the same as relativistic speed. The greater the gravity field, the slower time moves. In fact, time stands still inside a black hole. As for the "problem" of spatial displacement for a time traveler, have it anyway you want. Since backward time travel is impossible, the argument is academic.