My wormhole generator from Ikea (Würm) has just arrived, and is sitting in my living room ready to be assembled. Once complete, it’s supposed to look like a circular doorway six feet in diameter with a computer console attached. I punch in coordinates anywhere in the observable universe and it opens a wormhole to that spot. I can march on through my wormhole generator at my convenience and arrive at the coordinates without any time passing. I can go back and forth at my leisure, run electrical cables through it, play ping pong across it, etc.
Now, I’ve heard this is impossible because it requires faster-than-light travel, but hey, I found it in an Ikea catalogue, and they’re doing crazy stuff with unobtanium these days.
So setting aside the problems of what I should do with this thing, the mechanics of how it works, the reasons it’s impossible, and whether it will clash with the rest of my living room décor, I have one central question I’d like to discuss: you’re supposed to be able to violate causality with FTL travel. I should theoretically be able to use my Würm to become my own grandfather, or win tomorrow’s lottery. How precisely would I go about doing this? Please provide step-by-step directions.
(GLaDOS jokes welcome, but let’s please address the actual question first.)
You cannot travel FTL through space. Your wormhole generator circumvents this issue by bringing your current position and desired destination next to each other.
No, the wormhole generator, like all methods of achieving an FTL effect, is still capable of time travel. The key is that “simultaneous” isn’t universally-defined in relativity: Your wormhole takes you to a different place at the same time, but “at the same time” depends on your frame of reference. So what you do is, you shift yourself and your device into another frame of reference (by moving at some speed), and then you use it to travel to some point that’s “at the same time” in the new frame of reference, but which was at a different time in your original frame.
What you do is transport yourself onto a spaceship that is some quite far distance away. This takes place instantaneously in your reference frame. You then ask the pilot of the spaceship to accelerate by some fraction of the speed of light. As he does so, you will be shifted into a different reference frame by the acceleration. You then step back through the portal. This brings you back to Earth instantaneously in the reference frame of the spaceship, but (if you’ve done everything right and accelerated in the proper direction) in the reference frame of Earth you will emerge from the portal before you left.
Having a wormhole on the other end raises some questions about what the wormhole is “attached” to–does it stay in the local inertial reference frame? Is it influenced by gravity or other forces? Etc.
Let’s suppose instead that your wormhole consists of two circular doorways, and that you can pass through one end and come out on the other instantaneously. You can move the doorways relative to each other.
Let’s further suppose that each door has a clock on it that comes synchronized from the factory. When you enter one door with labeled time X, you come out the other door with the same time X.
But now suppose you accelerate one door to nearly the speed of light, and then bring it back to be next to the other door. Due to time dilation, the unmoving door will age more than the quickly moving one. As such, the clock on it will be advanced by some amount–say, an hour.
So now both doors are in the same room and you enter the younger door at 6:00. Your own experience is only consistent if you see 6:00 on the other door coming out–but that happened an hour ago for other observers in the same room! So their experience is only consistent if you emerged from the other door at 6:00 by the reckoning of the other door, which is before you entered the first one.
So there’s no way to make it all work out. Due to special relativity, every portal must also be a time travel device and hence cause paradoxes.
And the principle is evident every day, to a very small amount, on a people scale? When I leave my wife at home and run (while quickening my pace) to the bus, then run back home (while slowing the pace because I’m out of shape) because I forgot my keys, my “consistent existence,” as you put it, is ineluctably at odds with my wife’s perception of it?
Yes, but so long as you didn’t run to the bus at faster than the speed of light, you can’t violate causality this way. Furthermore, unless you run very, very fast, the shift in reference frame is going to be absurdly far below the limits of human perception.
Now, if you were wearing an atomic clock for a wristwatch, and synchronized it with your wife’s clock before you left, and then replace your run to the bus with a trip to the moon and back, you will find a detectable difference between your clock and hers when you return. Still probably below the levels of human perception however.
Somewhere, I read something on the subject, once upon a time. (Sorry, no cite.) It was claimed that scientists who study these things have measured the time dilation of the circumference of a 33 1/3 RPM record, relative to the innermost track of the same record. It’s some small number of billionths of a second, or some such. I wonder how they measure that.
(But no, there’s no part of the record that’s going backward in time relative to any other part of the record. That would sound very funny when played.)
Relativistic effects can actually be measured for speeds as low as a small fraction of a millimeter per second. Not only that, but there’s a good chance that you already own equipment capable of doing the experiment. In a typical electric circuit, the electrons are moving through the wire at the merest crawl, but that movement will still deflect a compass needle. And that’s a purely relativistic effect.
I thought that was merely an electromagnetic effect…
(And, yeah, well, the two are linked, certainly; the speed of light is a constant that pops up in Maxwell’s equations. But your phrase “purely relativistic” strikes me as wrong somehow…)
first you need a bet on something, say a game that is taking place on earth, second you need to place this bet someplace really effing far away (sort of, for a football game say 4 light Hours away) now while on earth you watch the game, see the outcome of said game, then step through your wormhole to planet welikeearthfootballforsomedumbreason and place your bet on the game.
grats broken causality.
The way that electric and magnetic force are linked is through relativity. Take a moving charged particle next to a current-carrying wire. The particle will deflect due to what we normally call magnetism. But in the reference frame of the particle, it has no magnetism; only electric charge. From its perspective, it deflects due to the slight difference in charge density of the wire (an electric effect), which happens because the moving charges in the wire have undergone length contraction (despite them only moving at millimeters per second).
So while the unmoving observer sees a neutral wire and two magnetic objects, the moving observer sees an unmagnetic particle and two charged objects.
There’s nothing more right about either perspective–neither the magnetic or electric force is privileged in this regard (though the electric force squeaks out a minor win until we observe a monopole).
AndrewL has it, but to elaborate a bit further: special relativity did force us to give up some properties of what we might call the “consistent experience”. For instance, two observers may disagree on the ordering of two events which are causally disconnected–that is to say, the events are far enough apart that they could not have influenced each other, even at light speed.
However, all observers must agree on the order of causally connected events. There still might be a difference in the exact timescale, but there cannot be a case where A causes B in one frame and B causes A in another.