We know that time and velocity are related. That is to say, as your speed increases, time for you slows down. Refer to the old example, “if a man gets into a craft and travels for an hour at the speed of light, when he returns, he will be an hour older, but someone who was a baby when he left, would be an old man when he got back.”. I’ve read about this theory actually being proven with high speed jets, and chronometers that are accurate down to the microsecond. After synchronizing the chronometers, one was flown at high speed, while the other was left on the ground. When the two were later compared, there was a difference in their times. A small difference, but a difference none the less.
So, can it be said that the velocity of our planet controls the rate at which our time is measured, in comparison to other planets? For example, we are what, about 2/3 of the way out on one arm of our galaxy, right? So, are we going through time at a different rate than a planet that might be closer to the center of our galaxy?
Time is relative. Every piece of matter, every atom, is going through time at its own rate. Normally, however, every atom of your body (and the earth and the sun) are close enough so that we’re we can talk about a common time without significant inaccuracy.
When we start measuring time relative to things that are moving relative to us very quickly (more quickly than normal astronomical events move) we have to take relativistic effects into account. Usually, however, only very very distant objects are moving fast enough (due to hubble expansion). Extremely massive objects (like black holes) also require relativistic calculations. Lastly, relativistic quantum effects govern the behavior of matter in extreme states, such as in a white dwarf or neutron star.
IIRC, the difference in orbital velocity (or even absolute orbital velocity relative to distant galaxies) is not sufficiently great as to need relativity for more than the most fiddlingly accurate measurements.
Time travel is impossible (or at least HIGHLY improbable…search for other threads on that though). Moving through time at a different rate than, say, a spaceman is not time travel. Time travel supposes I can go into the future or past and return to the present. Sapceman Spiff can’t do this.
FYI: Clocks moving at different rates has been observed by no more than placing one clock atop a water tower and another at the base (hyper accurate clocks). Light climbing out of earth’s gravity well changes speed hence time moves at different rates. I may have this reversed but the higher up you are the longer you will live. Mind you, over the course of your life the difference will only amount to a second or two.
As another aside the astronauts on the Mir Space Station that stayed up there for 6 months aged about 3 seconds less than everyone else on earth before they came back.
The time dilation deal doesn’t become extreme till you get VERY close to the speed of light (i.e. past 99% light speed).
yes, i am moving forward in time continuously, then there are days when i feel a bit behind, but i’m not sure that constitutes time travel, or just delayed bar drinking/time lag.
Well, he can’t go quite at the speed of light, but if he’s just going close to the speed of light, then you’re right.
Quoth Jeff_42:
Yes, you do have it reversed. A person on Earth will live to see a later date than a person in freefall. Note, too, that you won’t really live longer in any practical sense: Your age will still be the same by any clock that you bring with you, including such “clocks” as the number of heartbeats of thoughts that you have.
On to the question posed in the topic of the OP: Time travel (in the good ol’ sci-fi sense of going into the past) is possible if and only if faster-than-light tavel or its equivalent is possible. By equivalent, I mean any method that can get you from point A to point B before a photon travelling through vacuum could get there: This includes warp drives, wormholes, and any other quirks that might allow such nifty travel. As to whether FTL or its equivalent is possible, we don’t know yet, but we think that we’d need matter with negative mass to pull it off. Unfortunately, nobody really knows whether negative mass can exist, although we’ve never observed it, so don’t get your hopes up.
I went time traveling just last weekend! I went back to 1969, in fact. In 1969, I was in 4th grade. I was learning my multiplication tables. The boys in the classroom all had bangs and the girls all wore bell-bottom pants. When I went back, of course, I was again in 4th grade learning my multiplication tables. The thoughts that were in my head were the same as they had been (always are) in 1969, including lack of awareness of anything that occurred later, such as my present life. My experience of myself in 1969 was vivid and entirely present-tense. Of course, when I returned to current temporal location, I had only a badly faded and vague memory of 1969, because that is what the contents of my mind are like concerning 1969 (and possibly a few other things) these days.
Actually, I am time traveling to 2000 from the future. The contents of my mind right now include no awareness whatsoever of whatever future year I traveled from, because that is the definition of the contents of my mind at the moment. However, I’m well aware of the here and now, which seems quite real to me. If I travel back to the future, I won’t recall these days anywhere near as well and they will seem like dim memories of days gone by.
Time is a dimension. Just as you can say with regards to the other three that, at 2 meters out from the shallow end, the pool is 20 meters wide and 2 meters deep, you can say that at 2000 years out from the Jesus end, the AHunter3 person is sitting at a desk in Inwood, drinking Presidente, and typing a posting for the Straight Dope Message Board. And every time you look at 2000 and consider the location of AHunter3, you get the same answer. And, just as the pool has no definition and no meaning at 9700 meters above sea level (it doesn’t occupy that space), there is no “me” that can still be “me” and occupy a time that I did or will not occupy. (Can’t time travel to 1703, I don’t exist at those coordinates). And for the times I can travel to, I continue to occupy the same space (physically, conceptually, and otherwise) that I did/will/whatever any and every other time I checked out being at those coordinates. So although AHunter3 occupies a continuum beginning in the fading days of the 1950s and extending to some other finite date at the other end, I am only strongly aware of whatever part of that continuum I happen to be thinking of as “now”. At any point, I can look backwards (with limited recall) but not forward, which contributes to the illusion that I am always MOVING forward from then to now and cannot go backwards or jump forward skipping what is in between.
Sorry, no time travel a la H. G. Wells. It doesn’t work that way.
It does work that way IF there exists matter with negative mass. Your swimming pool example is a good one, but it doesn’t rule out time travel. It just means that the swimming pool has some parts that we didn’t know it has. How do you know that you don’t exist at 1703?
You’d also need to assume that negative mass has negative inertia.
I like to take the simple approach, if going backwards in time is possible where are all the time travelers? Maybe our present and past just aren’t time travel hotspots and most time travel agents won’t bother booking a trip out here.
You sure about this? I thought if you did some trick like tunneling through a higher dimension you could travel great distances without time dilation/travel being an issue.
I.E. I have a ‘dimension door’ next to me. If I walk through it I am in the Andromeda Galaxy somewhere. My total speed was 3 mph (walking speed) although I moved several million light years ‘instantly’. A photon leaving earth would take millions of years to get where I am unless it passes through the dimension door in which case it gets there instantly as well hence no time violations occur.
Think of it this way…two photons leave my ray gun. One circumnavigates the earth and one tunnels straight through. The one going through the earth has less distance to travel than the one taking the long way around and arrives at my detector in China first. No time issues…
I thought ‘Warp Speed’ (ala Star Trek) was kinda like bunching up (or ‘warping’) a table cloth. When the tablecloth is smooth you have a long distance to travel to get to the other end but if you bunch up the cloth in the middle you shorten the distance between you and your goal making it seem like your moving faster to reach the other side (when in fact all you’ve done is shorten the distance you need to travel). Hence no time problems for the crew of the Enterprise (or Klingons or whoever).
In MOST circumstances, when you add the consideration of other dimensions, you add to rather than reduce the distance between observed points. Are there any two stars in the two-dimensional sky that end up being closer to each other once we comprehend the sky as having depth? Only relative to other star-to-star distances, right? Whereas, two stars that look like they are side-by-side can turn out to be a hundred light-years away from each other.
The “warping” sounds great, but discovering how to move in directions defined by a hitherto-unknown dimension does not in and of itself tell us how to warp. I know where Alpha Centauri is in 3 dimensions, but knowing that doesn’t let me neatly fold distance and walk across a la Madeleine L’Engle’s tesseract. I suspect that dubbing in 4-5 extra dimensions would leave me in the same situation.
All of the above would seem to apply to time as well.
I thought higher dimensions (past 4) got all bundled up into the size of a pea at the creation of the Universe (one theory I heard of ‘where’ everything came from just prior to the Big Bang were a bunch of dimensions wrapped up with each other…dimensions 1,2,3 and 4 split off with 5 and beyond shriveling up).
The mind bending piece of this is that while they are pea-sized they touch all parts of the 4-D Universe we inhabit. Basically, if you can figure out how to open a window through the 5th dimension, you travel through the distance of a pea to get anywhere else in the Universe.
Of course, I realize this is nigh impossible as far as we understand things now but for speculations sake I thought this was how it was supposed to work.
I believe there was a little article about this in Popular Science/Mechanics (I read them both and so I can never remember where my info came from) a while ago. Supposedly NASA or someone has come up with a plan to do this or something like that. I’ll try and look it up, if I can find the mag. IIRC, the article was not about time travel, it was interstellar travel within human lifespan.
Perhaps, in the future, time travelers know that any contact with people in the past could cause a paradox, and just come and observe. Maybe those strange lights in the sky, aren’t really from another planet… maybe they’re from our own future… ya think?
Actually, we are all time travelers. We are currently traveling into the future at a rate of one minute per minute. As we near the speed of light, we can (in a sense) speed that process up, traveling into the future faster (at least the future of things around us). The tricky part is going backwards.
Here’s one to think about. If time and velocity are related, would time stop if everything in the universe stopped? I mean, if everything just stopped in it’s place. There was no rotation of anything. Nothing moved as far as planets, galaxies, etc… Is time dependant on motion?
The idea of a space/time warp is all well and good, but if you want to “warp” from point A to point B and the way to do it is to bring point B and point A together, how exactly are you, at point A, going to exert the force that will “grab” point B and bring it to you? Seems to me you’d have to have an accomplice already at point B to pull it off. Any other method is inherently tautological – in order to exert a force that reaches point B, you have to be able to exert a force that reaches point B.
Gravity. The article I was referring to (see my previous post), IIRC, stated that gravity could shorten the distance between two points by actually compressing the space between them. I think.
A wormhole is not a warp drive, its just a warp. A warp drive could/might/maybe work because we don’t know how fast spacetime itself can move, by crunching spacetime in front of the spaceship and expanding it behind it you can move great distances while only going relatively slow. Of course this relies on negative energy and negative inertia to make it work, but you don’t need anyone at point B.
I can’t remember where I read this and can’t explain why the scientisit proposing it felt like it should work this way but here it is anyway–> Supposedly if time travel were possible you can not go farther back than the time when the time machine was invented in the first place. So if a time machine is invented on June 1, 2000, then future time travelers can only return as far back as June 1, 2000.
Anyone else out there remember this theory?
Absolutely. You just have to think about it a bit differently (read Flatland by Edwin Abbott for a good take on this).
Say you’re a 2-D person living on the surface of a sphere…we’ll call you Spot. You see a ‘star’ on the opposite side of the sphere (you can do this because light has to follow the 2-D curve of the sphere so it ‘bends’ around the surface just as light bends in 3-D when passing a star or other massive object). As far as Spot is concerned he lives in a flat universe. To get to the star he just has to walk in a straight line (to him) to reach it.
Enter 3-D person…we’ll call him AHunter3 ;). AHunter3 says, “Look…you can go through the center of the sphere you live on and get to the star faster because it’s a shorter distance!”
Of course Spot thinks AHunter3 is out of his mind and while that may be true AHunter3 is still correct.
The same may also be true of 5-D space and beyond. I’m not saying this is practical or possible but it may certainly work that way could you pass through the 5th dimension.
Actually the other dimensions are wrapped up into a ‘ball’ with a size equal to the Planck Length (10 to the -33 power centimeters or about 100 billion billion times smaller than a proton). Also, if the stuff I read is to be believed, it’d take about 10,000,000,000,000,000,000 (19 zeros or 10 quintillion) electron volts to crack into this little dimensional ball.
I guess that means we won’t be poking our fingers in there anytime soon!
“Maybe those strange lights in the sky, aren’t really from another planet…”
You mean you actually believe they “really” ARE from another planet? It’s this kind of drivel that takes credibility from the REST of your drivel. Get a grip, ace.