In Star Trek they are ‘warping space’ so the effect is them going fater than the speed of light while in fact they aren’t really breaking any laws of the universe. They are in effect shortening the distance they have to travel while still going slower than the speed of light.
Don’t believe me? Try this…the particle he is referring to is one that actually hit the earth’s atmosphere and was calculated to be moving at v = 0.9999999999999999999999951 c
Jeff,
Seriously man, how does that indicate that exceeding the speed of light = traveling back in time.
And another thing. The OP postulates a faster than light method of transportation. It doesn’t say that that method of transportation won’t involve wormholes or warping space or magic carpets. So saying things like “and didn’t jump through a wormhole or something”, or “and no sneaking through hyperspace and screwing my post up,” is just bad form man.
It’s possible the OP’s trick would work even without the starship. I read somewhere (yeah, I know, typical Internet cite) fairly recently about some scientist who had come up with a theory involving black holes.
We know that gravity bends light. The theory here is that a black hole of just the right size could bend light at just the right angle so that light coming from Earth (say) 5,000 years ago would be bent just the right amount that the light would hit the Earth where it is today. Given a powerful enough telescope, it would therefore be possible to “see” the Earth as it was 5,000 years ago.
Now, the odds of this occuring are small enough to be considered nil, but as a thought experiment it does seem to make sense.
OK, let’s (hopefully) clear this up once and for all… Forget about the nifty telescope, that’s perfectly within the well-understood laws of physics as we now know them, and hence boring 
. According to Einstein’s Special Relativity, if you have ANY method of leaving point A and ending up at point B before a photon travelling through vacuum got there (which was emitted when you left), then you can accomplish real, honest-to-goodness time travel. Never mind about worm holes or magic carpets or other oddities, all that matters is that you can get there and beat light to it. Also note that I’m not just talking about viewing the past, or just going into the future at a faster rate (both easy), I’m talking about the whole shebang, go-back-and-murder-somebody-else’s-grandfather time travel (murdering your own grampa may or may not be possible, but it’s almost certainly unwise). Knowing this message board, somebody’s going to eventually ask me how to manage this, but I need a nap now, so I’m going to wait for you to ask
Actually, what tanstaafl mentioned is close to what caused me to think about this in the first place. I read an article (I think in the science and technology of The Economist, but a quick look through the archives didn’t come up with it) about a similar phenomenon that scientists have observed.
Upon close examination, scientists discovered that galaxies that appeared to occupy the same degree or so of arc in space (if that’s the right term; what i’m trying to say is that they almost overlap in the night sky) were actually the same galaxy. Some of the light from it was getting bent by summat (nebula, etc.) on the way to Earth, causing it to take slightly longer to get here, and offsetting the two images somewhat. Hence, two images of the same galaxy, one X years older than the other.
-ellis
and jeff, I just don’t understand what you’re trying to say. could you please expound a little more?
and…
Bad Form? Seriously man, why are you getting your panties in a twist over this? I was merely restricting the variables of my question so I could get a meaningful answer to a meaningless question (althoug how meaningless I’m not sure…haven’t some serious scientists speculated on Tachyons as being able to achieve faster than light velocities or is that pure science fiction?). If you said you were jumping through wormholes or going Warp 9 you wouldn’t violate relativity and get time twisted-up. I want to know if time would reverse itself.
So the question is simply…
If you do the mathematics relating to time and the speed of light does going faster than the speed of light cause the time portion of the equation to reverse itself or do the equations fall apart and become impossible to get an answer from?
My post above indicates that suggestions of watching Star Trek is a lame answer my question. The Starship Enterprise has an apparent speed greater than the speed of light. It is not itself going faster than the speed of light. Hence a clock on the Enterprise takes 21 years to get to the center of the galaxy going 1516 times the speed of light while a particle going not quite 1/1516 the speed of light gets there in 3 seconds according to its clock.
It illustrates how time dilation increases as you approach light speed…then time stops at light speed…is it fair to assume that time goes backwards past light speed? That’s why I’m asking this question.
Jeez…
Sorry if all this counts as a hijack…I didn’t mean it that way…I just want what should be a simple answer from someone who would know (I believe there are some people among the Teeming Millions who can answer this).
Chronos:
Thanks for the answer Chronos. When I wrote my last post I mustn’t have updated my browser and never saw your reply before writing mine (an hour later I saw it though).
ellis555:
Maybe my last post wasn’t a total waste. Does it explain better what I’m getting at?
Chronos says:
I say:
Dude, are you high? Go rereaed whatever the book you read that in. If it says the same thing the second time around, throw that book out.
Jeff says:
I say:
Relativistic equations dictate that it is impossible to accelerate up to (or past) the speed of light. Time contracts as you approach the speed of light, but assuming that it reverses when you pass the speed of light is a mistake, because it is pretty clear from the theory that you can’t pass the speed of light.
On a side note about Star Trek. Relativity states that you can’t exceed the speed of light locally, but not globally. Star Trek uses the warp field to change the shape of space so that the ship is not exceeding the speed of light locally, but would appear to be exceeding the speed of light when observed from anywhere in the universe except where the ship is. Good luck making an engine that does that.
Is FTL travel impossible? Probably. If it is possible, it would require something like wormholes, or warp fields, or hyperspace, or something else. I don’t find any of these to be very likely to work out, but you never know.
I hope Ellis does manage to get these things working though. I think ellis should also make his super-duper telescope with the ability to see through walls. Then we could spy on Marylin Monroe in the shower.
Jeff_42 -
I do have a better idea of what you’re getting at now. I must confess that I don’t have much of a grasp of the crazy-haired guy’s theories, so I can’t really debate you on the time reversing itself aspect. Hopefully chronos will make things a little clearer for me.
Lance Turbo -
If you want to see the lady naked, you can always go buy Playboy. Now, what I’m interested in is seeing if Helen of Troy was all she was cracked up to be.
-ellis
I agree 100%. It’s absolutely impossible for an object with mass to reach the speed of light needless to say exceed it. I said as much in earlier posts and I’m clear on that point. Still, it doesn’t mean you can’t sit down with Einstein’s equations and figure what might happen if you could go that fast. Not to mention all the fun you can have afterwards thinking about how (assuming time reverses itself) you could arrive at your destination before you left! Ellis could look back with his Uberscope and see himself walking around on Earth before he left. Only one of many reason the Universe probably doesn’t allow such things…
I also agree 100% with your take on Star Trek. Sitting on the Earth watching the Enterprise whip by at Warp 9 I’d measure its velocity at WAY above the speed of light. The guys on the ship however aren’t experiencing speeds anywhere near the speed of light…part of the reason they don’t return to Earth 3,000 years in the future when they only took a spin around the solar system for a week (their time). The Oh_My_God particle described above may take 3 seconds its time to reach the center of the Galaxy but thousands of years would pass on Earth before it arrived.
Goes to show it’s all relative
Ok, folks, sorry this took me so long, but I’m just finishing up finals week here. WARNING! Physics follows
Ok, the first thing we need to address is the concept of simultaneity. Basically, there ain’t none such. In relativity, if in one reference frame two events are simultaneous, then in another frame moving relative to the first, they won’t be.
Consider three observers, Alice, Bob, and Charlie. Charlie is moving to the left relative to Bob with a speed v, and Alice is moving to the right with a speed v, again with respect to (WRT) Bob. They all pass each other at the same time, and agree that they’ll call that time t=0, and that position x=0. An important note here is that each observer considers himself to stationary, and the other two to be moving-- so, for instance, Alice says that her position is always x=0, and likewise for Bob and Charlie.
Now, somewhere, somewhen, two flashbulbs go off. Both bulbs are stationary with respect to Bob, and according to him, the first flash is a distance x=X_b to the left of him, and the second is the same distance right of him. Let’s also assume that the light from both bulbs reaches Bob at the same time, which happens to be t=0. Since the speed of light is constant, Bob concludes that T_1b = T_2b = -X_b/c , so in Bob’s reference frame, the two flashes were simultaneous.
Now let’s look at the same situation from another frame of reference, say, Charlie’s. Since Charlie is at the same position as Bob at t=o, he also sees both flashes at the same time. However, since Charlie is moving left at v WRT Bob, that means that Bob and the bulbs are moving to the right at v WRT Charlie, so that the flash 1 was farther away when it went off than flash 2. Now, since he sees them at the same time, he interprets this to mean that flash 1 went off at an earler time than flash 2-- a correct interpretation, in his reference frame. Specifically, (X_2a - X_1c)/(T_2a - T_1c) = c²/v .
The same reasoning can be applied to Alice, except for her, flash 2 went off before flash 1, and (X_2a - X_1a)/(T_1a - T_2a) = c²/v .
In other words, one observer sees one event as happening first, one observer sees theother as happening first, and another sees them as happening at the same time. Now we’re ready to tackle the original question, that of FTL (Faster than light) travel. Here, the two events we’re interested in are the ship leaving one point, and it arriving at another. It doesn’t matter what happens in between, it could be a hyperjump, or a wormhole, or a magic carpet, or anything else you feel comfortable calling it-- The point is that the ship is at one place at one time, and another place at another time. Even though the ship might not be actually “moving”, let’s define an effective velocity: V = (X2 - X1)/(T2 - T1) . Now, since we’re talking about an FTL ship here, V > c .
All right, let’s define some more reference frames again. Alice is on the Earth, Bob is moving left at speed v = c²/V with respect to Alice, and Charlie is moving left at c²/V with respect to Bob. Similarly, we’ve got Diane moving right at c²/V relative to Alice, and Edgar moving at the same speed relative to Diane. A few points to note here: First, since we said that V > c, c²/V < c , so all of our five observers are going at ordinary speeds below the speed of light. Secondly, relativistic velocities don’t add like normal velocities, so we can’t just say that Edgar is moving at a speed 4c²/V relative to Charlie. In actuality, the relative speed is less than that, and guaranteed to be less than the speed of light. The way we’re going to approach this, though, we don’t need the exact formula for velocity addition, so it’s just something to keep in mind.
Ok, now, ellis555 gets into his nifty keen-o Ellismobile on Earth, and kicks on the (normal, sub-light) engines to match velocity with Charlie. Having done so, he then activates the flux capacitors, or tells his helmsman “Engage”, or whatever it is he does to travel FTL, and jumps to the right at an effective speed V, from Charlie’s point of view. Now, this means that for Charlie, (X_2c - X_1c)/(T_2c - T_1c) = V = c²/v . Now, remember our discussion of simultanaity above? When, according to Charlie, event 2 happens after event 1, subject to that formula, they’ll be simultaneous according to Bob, and according to Alice, event 2 happened before event 1.
Now, ellis555 turns around and matches velocity with Edgar, and jumps the same distance (according to him) to the left. The same thing happens: Edgar claims that the ship moved at FTL speed, Diane claims that it jumped instantaneously from one point to the other, since its departure and arrival were simultaneous, and Alice claims that it went back in time again, and all three claims are correct, for their respective frames of reference. If ellis555 then kicks in the normal engines again and brings himself to a stop relative to the Earth, then the net result is that according to Alice on the Earth, he departed a given place at a given time, and arrived at that same place, at an earlier time. Time travel, in other words.
Q.E.D.
chronos -
Thanks. But what I really want to know is…if you’re taking finals right now, and mine aren’t for another four weeks, can I travel back in time and kill you for being done before I am without disrupting the space-time fabric?
-ellis
oh. and how would things appear to me, in my spiffy ship? i assume that i would age X days subjective to me (however long it felt like the trip took to me). but what would things on earth look like to me? would the calendar show a day earlier than i left, per what alic back on earth experienced? or should i go enroll in that physics class that i’ve been dodging so far?
Nah, just go back a few years and tell yourself to apply to my school, instead of where you are now
As to what it would look like, I don’t know what you’d see if you looked out the window of your ship-- That would depend on how you managed the FTL. When you got back, though, your calender would agree with the time according to you, and Alice’s would agree with her, but they would not agree with each other. In other words, if you pulled this stunt right now, and went a day into the past, and took a day to do it, your time, then when you got off the ship, your calender would read May 7th, and a calender that stayed on Earth would read May 5th. Which one is “right”? Depends on why you want the date. If you want to celebrate your birthday, use the calender that went with you; to celebrate Alice’s, use hers. Or just party according to both calenders 
There were enough parties last night without it being anyone’s birthday. But if I hop in my ship and go zip off into space, maybe I can come back and tell my roomate not to puke on the floor this time around. But this is getting a little mundane and pointless, so I think I’ll let the thread die unless someone has a scientific point to raise.
Thanks for all the input.
-ellis
I’m confused. How does 0.9999…c > 1516c (c being greater than 1?)
I liked Chronos’s explanation. If anything travels FTL, then there exists a reference frame where that thing travels backwards in time.
Lance Turbo
As much as I like Star Trek, I would not recommend Star Trek to learn about relativity. They play fast and loose with GR. There was one episode where the ship managed to escape a black hole by going through a “crack” in the event horizon.
Why are you trying to apply real physics to a unrealistic situation, FTL travel. If FTL was possible there would be a new physics that would explain exactly what has going to happen and it would have little in common with physics as we know it.
If you brought this up at a cocktail party I’m sure someone will call you on it and ask you why you don’t just build a time machine in your story and save yourself the trouble.
I am not trying to apply real physics to an unrealistic situation. I am applying real physics to a situation of whose realism I am unsure, in an effort to determine how realistic it is. There is no such thing as “new” physics; all physics is simply an extension of “old” physics. When and if faster than light travel and time travel are discovered, they will be consistent with Einstein’s special theory of relativity, or at the very worst, consistent with some subtle variation of Special Relativity. Since we do not yet know what form, if any, that subtle variation will take, the best we can do in our thought experiments is to use the form of SR with which we are familiar. It is through such thought experiments using the existing theory that we will derive any new theories relevant to the topic.
As to matt_mcl’s question about how the OhMyGod particle can be considered faster than the Enterprise, it’s a question of how you’re measuring speed. If you had a race between the two, say from Earth to the center of the Galaxy, then from the point of view of an observer at rest relative to the Galaxy, the Enterprise would win hands-down. However, if you’re riding along on the particle or the ship, the trip would seem much shorter on the particle, because on the particle, time dilation would be so great that the journey would only seem to take about three seconds, wheras the crew of the Enterprise are magically unaffected by time dilation.
horseloverFat -
I don’t want a regular old time machine. Anyone, including yourself, can have one of those. I’m not trying to keep up with the Joneses, I’m trying to stay a step ahead. Hence my uberscope and spiffy ship.
As for the physics aspects of things, if you want to invent a “new” physics to explain my FTL craft, fire away. I’d be more than happy to see what you come up with. But until you come up with it, I’m even more happy to hear what Chronos has to say on the subject using plain old physics.
-ellis
Last I heard relativity replaced most tenets of classical physics. I don’t see it all as a lego castle that you keep building, things do get thrown out when better things arrive. ‘New’ physics.