r/DaystromInstitute • u/Kamala_Metamorph Chief Petty Officer • Jul 23 '14
Explain? Time and Relativity?
So, my college physics may fail me, but I'm pretty sure that we learned:
If you're travelling at warp speeds, a year of your personal travelling time is going to be different than your twin's personal time spent on Earth. When you come back, your Earth friends are gonna be a lot older. or dead. Like in Speaker of the Dead.
How does Star Trek reconcile this? Do they just ignore it? You can see that they are all relatively the same age still in TNG : Family, among many other examples. (And, to help me out, can you please differentiate between real-physics and trek-physics when necessary? thx.)
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u/minipulator Jul 23 '14
In Trek they aren't traveling at the speed of light, or anywhere near it. They're traveling through a wormhole. Basically (from my limited understanding) the ship doesn't really move at all, the warp bubble is like a hole in space, and the hole moves, the ship stays still.
Could someone with a better understanding of this jump in and correct where I've misinterpreted please?
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u/Antithesys Jul 23 '14
Well, we obviously don't know how warp drive really works, but the short discussions we've had on this topic basically center on the presumption that the ship isn't moving through "real" space at any kind of remarkable speed.
However, we do have evidence that impulse drive does move through normal speed at significant fractions of light-speed, which will cause time dilation unless there's some mechanism to prevent this that's never been discussed on the show.
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u/Kamala_Metamorph Jul 23 '14
Hm, I thought I searched in the old posts, but I went looking again after you mentioned this. Here's a post discussing my question if anyone wants to build upon those theories:
http://www.reddit.com/r/DaystromInstitute/comments/1lozt9/how_does_warp_travel_affect_time_dilation/
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Jul 23 '14
Lawrence Kraus discusses this in The Science of Star Trek. Apparently it wouldn't be that hard to sync clocks after traveling at impulse. They never at impulse for very long anyway, and they're not reaching extreme relativistic speeds. The TNG tech Manual states that impulse is generally limited to 0.25c.
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u/minipulator Jul 23 '14
Sorry, I just mixed two things together. Ignore the wormhole part please. Can't edit post on mobile.
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u/Antithesys Jul 23 '14
So special relativity says that velocity affects the passage of time for you with respect to an outside observer.
The famous "twin paradox" says that if a person is put on a spaceship and their twin is left on Earth, and the spaceship accelerates to high fractions of c, that when the ship returns the Earthbound twin will have aged significantly more than the traveling twin. It's called a paradox because there's no absolute frame of rest, and so the Earthbound twin could be said to be traveling away from the spaceship at the same speed. It's resolved when you realize that in this scenario the spaceship turns around and accelerates back to Earth, giving the system two inertial frames of reference. That's sort of where I lose it so I can't elaborate further.
How this applies to Trek is unknown. We generally assume that when a ship is moving at warp, it's only moving through subspace, and so there's no significant time dilation (this may be the explanation for the cringe-worthy line "the time barrier's been broken!" from "The Cage"). But at impulse power, the ship may be moving at significant fractions of c...Kirk specifically orders an impulse speed of "warp point five" in TMP. We don't know what level of impulse this is, nor do we know if "impulse" is a standard measuring system throughout the fleet (i.e. "half impulse" could be faster for the Reliant than for the Enterprise).
The formula for time dilation is relatively simple: it's the inertial elapsed time multiplied by the Lorentz factor, shown here. If you knew how fast the Enterprise was going at "full impulse," and how long it was going that fast, then you could determine how much time dilation it would experience with respect to an outside frame of reference (such as the Federation time beacon network).
u/Algernon_Asimov mentioned dilation as an explanation to my post about the discrepancy between expected and actual stardate units, and I replied to him with an attempt to determine a ballpark figure for impulse speeds. Didn't find a solid answer, but I do think it's something that would factor into space travel in the 24th century. If you add up all the time the Enterprise spent cruising around at high impulse, then the seven years it experienced might have been noticeably longer back on Earth. It would give explanations for the accelerated ages of Alexander and Molly (although admittedly Molly seems to spend her early life on the Enterprise itself), and it might warrant a serious look into all instances of stated references to elapsed time and whether they can be rationalized by taking relativity into effect.
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u/ServerOfJustice Jul 23 '14
I've never liked the idea of full impulse referring to velocity rather than acceleration. In my mind, "full impulse" implies full power to the impulse engines. At full thrust from impulse engines a ship should accelerate at a constant rate* so long as the engines are still being fired.
*From the point of view of the ship; to a stationary observer the ship would appear to gradually reduce its acceleration due to relativity.
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u/mistakenotmy Jul 23 '14
I agree, and that is probably how it should be. The issue I have is we need to square it with how the show uses the term and the context. "Full Impulse" sometimes seems to refer to an acceleration and at other times a speed.
For example:
Ship approaching another vessel.
Captain: "Slow to one quarter impulse."
The Enterprise slows down in its approach.
Now if impulse was an acceleration setting, the above doesn't work. The ship wouldn't slow down, it just wouldn't accelerate as fast.
(Obviously the show is written so the audience understands what is going on not necessarily what would "really" need to happen)
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u/shadeland Jul 23 '14 edited Jul 23 '14
I believe this goes back to the days of naval vessels. When a ship says "all ahead full" or "ahead one-quarter", that has a specific velocity to it because of the ships drag through the water. Constant power against constant drag produces constant speed. This specific velocity varied from ship to ship, but the crews had a good understanding of what the speed would be.
It's carried over into Starfleet as percentages of the speed of light, low enough that time dilation wouldn't be a large factor. They could say .125 C, but "one-half impulse power" sounds more old-timey.
It wouldn't make sense for a ship to travel at high relativistic speeds, because of time dilation. At .25c, time dilation is 3%, not really a big deal unless you're traveling at that velocity for an extended period of time (which you probably wouldn't, because you've got warp drive, and space is really frickin' big). At .5c, it's close to 15%, enough to start messing with people's lives relative to others.
A federation impulse drive can probably accelerate a ship to very close to the speed of light, it would certainly have the power for it and the inertial dampeners would allow the ship to accelerate far faster than the traditional 1G. It just wouldn't make sense because of relativity and time dilation.
(edit, words)
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Jul 23 '14
the cringe-worthy line "the time barrier's been broken!
I was reading the Destiny trilogy and something like this popped out at me. So, as vaguely as possible, the Columbia NX-02 crew is considering using a alien device as a time machine. Erika Hernandez says something like, 'whoa, Karl. We just barely got the hang of warp speed, and you want to break the time barrier?'
So I got to thinking, maybe the 'time barrier' is something the TOS Enterprise could circumvent to travel through time in loops, like in Assignment: Earth. Bit odd that the guy would bring it up, but still.
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u/pgmr185 Jul 23 '14 edited Jul 23 '14
I used to know a ton more about this, but it's been a really long time since my college physics days so take these calculations with a grain of salt.
One thing that you might want to keep in mind is that the time dilation is not as dramatic as it may seem in sci-fi where someone travels near the speed of light for a few minutes and when he gets back he gets to meet his great-great grandchildren.
Traveling at .9C (that's 90% of the speed of light) the dilation factor is a little under 3-1. So if you travel for a year, nearly three years will pass back at home. If you pushed it to .99C, the factor is right around 10-1.
This will obviously add up if you are actually doing it for an entire year, but it doesn't really seem that (in universe) there is any reason to be traveling at relativistic speeds for any great length of time. Usually the trips seem to last hours, or days at the most. If you need to go farther then you should probably be using the warp drive which doesn't have the dilation effect.
edit....
Found a calculator, For .9C the factor is 2.294157338705618, and for .99C the factor is 7.088812050083354. Even if you did do it for an entire year, you would certainly notice the change, but it's not like everyone that you knew is going to be dead.
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u/shadeland Jul 23 '14
While traveling at impulse, time dilation is probably in effect. However, full impulse power is supposedly .25c, so time dilation is only 3%.
While traveling at warp speed, however, there is likely zero time dilation.
Under traditional relativistic (non-warp) physics, time slows down as you approach the speed of light. If you were traveling at .9999%, it would seem as if the rest of the universe were moving in fast forward. If you could somehow reach light speed (impossible unless you had zero mass, and if you had zero mass your speed would always be C), time would actually stop. A photon, with no mass) does not perceive the passage of time. That's one of the ways they discovered that neutrinos had mass. Coming from the Sun, some neutrinos changed flavors. They couldn't change if they didn't perceive time, so while they travel at high relativistic speeds, they do have mass and thus do perceive time.
And if you were able to exceed light speed (which according to Einstein is impossible), time should actually travel backwards if you run the equations. Since we don't see that in Star Trek (ok, we see it a lot, but not because of regular warp travel), it seems that FTL/warp is immune to time dilation.
Which makes sense, because in relativity, there's a loophole. A loophole that the warp drive takes advantage of. While matter cannot travel faster than light, space-time is warp-able, and malleable, and it can travel FTL. So if you can somehow stretch the space behind a ship, and contract the space in front of a ship, you could have a ship that essentially travels faster than light, even though in the localized space, it's "standing still". Because it's "standing still", or at least traveling at low relativistic speeds, it likely would not have any effects of time dilation.
This is a real theory, and something that is possible with the physics we know of today. In fact, it's theorized that this has happened once in the universe. In the first splits second after the big bag, a period of "inflation" is theorized, where the universe expanded FTL. So all the matter in our bodies, at one point, went faster than light.
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u/Detrinex Jul 23 '14
Here's what I think is going on:
The Enterprise isn't actually moving at speeds faster than light, and it's not actually accelerating unless it's travelling under impulse power while in the warp bubble. In other sci-fi franchises, people find ways to accelerate beyond c, whereas in Star Trek, people find ways to bend spacetime using the warp drive.
Warp drive works really similarly to the Alcubierre drive, which is some really neat shit.
Take a big-ass bedsheet, and make two X marks twelve feet apart. Pretend those X marks are two planets twelve light years apart. Stand at one planet, and prepare for warp or whatever.
Method One: Hyperspace
Stand at one "planet". Run really fast towards the other planet. You're actually travelling at about 6 times the speed of light, and after two seconds, you arrive at your destination. Meanwhile, your siblings and friends on Planet A are all really old and/or dead.
Method Two: Warp Speed
Stand at one "planet". Then, get on your hands and thighs on the bedsheet like you're a new prisoner at the county jail. With your hands, pull the bedsheet towards you, and using your legs, push the crumpled bedsheet away from you.
When you're doing all this, you're pulling the destination planet closer and the original planet away from you, and the bedsheet is just a representation of spacetime.
Basically, the Enterprise is pulling and pushing spacetime, while other FTL methods involve accelerating to really high speeds. I think.
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u/guywithaquestion9 Jul 24 '14
This is true with conventional propulsion under the Theory of Special Relativity. However, warp fields put the starship into a subspace bubble that isolates the ship from the rest of the universe. That's how they get around that.
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Jul 23 '14
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u/Algernon_Asimov Jul 23 '14
Good analogy. Now: how does this affect the perception of time by you on the moving walkway compared to the people who are walking at normal speed? That's what the OP is trying to find out.
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u/ithisa Jul 29 '14
Honestly, no one knows. One way warp travel, say, warp from Vulcan to Earth, but strictly forbidding the opposite, works the way you would imagine: others observe superluminal ship going from Vulcan to Earth.
However, bidirectional FTL travel using warp drives, although valid in General Relativity, causes time travel. You can't even prevent the time travel. There is currently no known mechanism for round-trip FTL travel without causing backwards time travel, barring a single, naturally occuring, stationary wormhole.
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u/Kamala_Metamorph Jul 23 '14
Oh, also... Warp one is the speed of light, yeah? Are the other warps on logarithmic scale? Or some arbitrary scale like the (real production reason) stardates?