I was thinking about the straight road right outside my house. it continues in a straight line for about 1mile.

As i look toward the end of the road i think to myself, if i walk to the end it will take me about 20minutes, if i run it will take 10, if i cycle it will take me 3, if i go in the car it will take 1.

The speed i am travelling determines how long it will take.

i then thought about the road as if it were circling the earth. lets say that me and my brother started off in the same location and heading in the same direction, we set our watches to the same time, my brother travelling on a bike and me in a car. eventually i would come across my brother on his bike since i am travelling much faster than he is.
upon meeting again we check our watches and they show the same time.
since both watches show the same time, we were both in the same time frame regardless of our position and speed, and time moves at a constant rate.

if time moves at a constant rate here on earth, where in the cosmos would it move at a different rate if that location is known, is it possible to recreate the environment here on earth.

if it were possible to recreate that environment on earth what would we see if we looked into it.

im confused about time again.
that is all

Technically you and your brother are not in the same frame and your watches won't tick at quite the same rate. For velocity differences that small, though, the effect is really, really tiny and you'll never notice anything.

Two things change the rate at which time flows (relative to somebody else): relative velocity and gravitational fields. The faster you move relative to somebody else, the slower your clock will run behind his (although the effect is only noticeable when your velocity gets close to the speed of light). Being in a gravitational well makes time slow down, as well. A clock here on earth ticks slower than one high above us on a rocket because we're deeper in the earth's gravitational well. Again, the effect is pretty tiny because the earth doesn't have a particularly large gravitational field (you need to start dealing with things like neutron stars and black holes for things to get interesting).

We can recreate the first of these ways to slow time in a noticeable way here on earth by revving particles up to relativistic speeds in particle accelerators. A famous example of this, however, is provided by nature. When cosmic rays strike the upper atmosphere they trigger a shower of secondary particles, one of which is called the muon. Muons decay in about two microseconds which isn't enough time for them to make it to the ground. Yet they do make it all the way down (or at least a lot closer than they ought to). The reason they can manage to do this is that from our point of view time is passing more slowly for these muons; two microseconds on their clocks takes a lot longer than two microseconds on our clocks so they make it down (from the muon's point of view things are a little different).

Ok, so given that the differences are so small as to be unnoticeable, i may aswell stick to my guns and say that both me and my brother are in the same time frame regardless of our speed and position. my argument for this that we both travelling along the same plane in the gravitational well. you mentioned that differences would be small, but more noticeable depending on the location in the gravitational well. so if were both on the same plane, there cant be any difference.

I hope i make sense...

Right. Noticing any kind of difference requires conditions that we'd consider extreme compared to what we experience in our everyday lives. We don't travel close to the speed of light and we don't often find ourselves in the gravitational well of a neutron star so all this is sort of academic.

Even though you are both in the same gravitational plane the teensy weensy (unnoticable) difference comes from both of you travelling at different speeds. One is travelling slower relative to the other.

Thanks for your input, so we can rule out time travel in the human sphere of existance...
thank god for that, i wont ever have to think about time travel again.

case closed

I wouldn't say that. If it's possible then I don't see why we can't do it someday (maybe even in the not-too-distant future).

Let me throw in an adaptation of a summary of some possiblities for time travel I posted at another forum a while back. The schemes for time travel from established science tend to fall into a few categories:

Special Relativity

As we just went through a little bit, special relativity is the theory with all that jazz about traveling near the speed of light. Changes in masses, lengths, and most importantly here, time. You might call this one a one way ticket to the future; traveling near the speed of light slows time down for you relative to somebody not along for the trip. It's the Planet of the Apes scenario (made a bit more clear in the Boulle book than in the Heston movie but eh). Backwards travel doesn't seem to come up, unless you get into the speculative world of tachyons, which would travel faster than light. But those aren't thought to really exist and even if they did, it doesn't seem they'd let us travel back through time.

General relativity

This is essentially a more thorough version of special relativity, that actually amounts to a theory of gravitation. This is the one that talks about mass/energy curving spacetime.

Since arrangements of mass/energy shape both space and time in this theory, it becomes possible to manipulate spacetime in such a way that you get what're called closed timelike curves.

There are certain solutions to the equations of general relativity that contain curves that would allow some observer to travel into his future but arrive in his past. Normally you follow a path through spacetime that leads from past to future--these special paths, however, loop back and intersect themselves in the past. In GR these timeloops are the closed-timelike curves.

The problem is that to get spacetime to act like that you need to figure out what configurations of mass and energy will do the trick. Goedel found the first one a half century ago--in a non-expanding rotating universe it's possible to travel around and follow one of these time loopy paths (the trick lies in the fact that if you send off a beam of light in such a universe it will seem to do a kind of U-turn as the universe revolved around it--so you can take a kind of shortcut and head it off).

Others ways to produce these closed timelike curves involve some of the weird arrangements of matter you've probably heard of if you've ever looked into time travel--rotating, infinitely long cylinders or Gott's idea of two cosmic strings (very dense, very thin, very long massive filaments out in space--theoretical toys as of now) flying past each other both create geometries that allow timeloops to exist. Playing with wormholes can also lead to CTCs.

Some argue that such solutions to Einstein's equations aren't physical and that they're only mathematical gags--they simply can't arise physically. Others argue that nature conspires against such timeloops and that they're immediately destroyed if they should ever arise (that's Stephen Hawking's Chronology Protection Conjecture)--so we (and apparently causality) are safe.

But many physicists take them very seriously and believe they may very well exist (or at least are able to exist). J.R. Gott (the guy with the cosmic strings above) has suggested that a closed timelike curve could explain where the universe came from--namely, itself (I posted about this in a thread in the science forum about what came before the big bang). There are papers out of the Institute for Advanced Study suggesting that CTCs in computers could make solving difficult problems a lot quicker and a lot easier.[/quote]

General relativity also allows another kind of "one-way ticket to the future" time dilation that doesn't involve zipping around at near-light speeds. This variety is called gravitational time dilation and relies on the fact that clocks tick more slowly in gravitational wells--clocks at the base of a very tall tower tick ever so slightly more slowly than clocks in the top-floor penthouse. The stronger the gravitational field, the more pronounced the effect. If you take a bunch of mass and construct a kind of shell around yourself or take a little trip down near the (very hazardous) surface of a neutron star, you could wait a while then climb out to find time outside your gravitational well was going faster and you're "in the future." This is what we were just talking about above.

There are other senarios, like this one (from an old paper on this subject called Constructing Time Machines):


Unfortunately, after analyzing what happens if two such shock waves head straight for each other, the author concludes that answer to that one is "no." But even though that one doesn't look like it works out for would-be time travelers, the fact that there are such possibilities at all should be encouraging.

Other oddities of spacetime geometry that general relativity might allow to exist could also function as time machines. Wormholes would be links between different spots in space and, conceivably, time. A Caltech physicist named Kip Thorne and a couple grad students wrote a paper a number of years ago analyzing how a wormhole could conceivably be not only constructed but turned into a time machine. So there's that.

Quantum Mechanics

This is another area of physics time-travel enthusiasts sometimes look to; this is the way things operate on the very smallest of scales.

Take a look at this New Scientist article concerning work that seemed to indicate that (while allowing travel backwards through time) quantum mechanics doesn't allow paradoxes. Convenient. :



There's also some stuff that could be said about an idea called Wheeler-Feynman absorber theory that utilizes light that goes backwards through time. But this is long enough as it is, I think.

So there's hope.