time travel

[businessman07]

Re: time travel

Einstein's special theory of relativity basically explains that time travel is a unique possibility, but only if we can create a machine which would cause us to travel at close to the speed of light.

I was thinking about that, and even if we could travel at the speed of light how would that enable us to go backwards in time?. Not questioning you, just einstein.

When you think about it, what is time travel? It is one traveller experiencing time relatively different to another. Einstein's theory explains that a person on a train going near the speed of light will experience a second pass by, while the bystander will experience 60 years pass by. Creating such a "train" (though to build a contraption that could achieve such a speed or "carry" a human is insanely difficult) would ultimately result in the creation of a time machine.

this does make sense, but wouldnt the person on the train still be moving foward in time even if just one second passes? I guess I can't see it because no matter how fast you move time is still going to stay the same speed. thats why I agree with this.

As much as I agree, it is impossible to prove this, since how time actually functions is not properly understood.
A measurement is defined as such by whoever is measuring. We define time as we understand it, but it could be something more complex, even though I doubt

[Reach]

Re: time travel

Buisnessman, Traveling near the speed of light causes time dilation, because of mc^2/(1-v^2/c^2). Time dilation at high speeds means that time outside of your perspective will pass very quickly (like on earth, 1000 years could pass for 1 of your years). So yea, it is impossible to go backwards with this method, and impossible to come back, because you're just changing how time is observed, thus it's not really time travel. As an example, I would compare this to living for thousands of years. If you lived for thousands of years, things would pass, people you know would die, and the times would change all while you barely age at all. You're not time traveling by doing this either, you're changing how fast your internal clock ticks. If someone outside your super fast ship could see a clock inside of it, it would not move, and if you could look out your window near the speed of light everything around you would be happening in the blink of an eye (theoretically, though because of how light works things will become increasingly 'white and you won't see anything, not to mention you're going to be dead XD).

For this reason near the event horizon of a black hole you could theoretically see the end of the universe, however, this is not a practical application. You'll die long before any of these time dilation effects take place, because time only dilates extremely as an energy approaches infinity.

As an example, at 97% the speed of light time is only going to be happening 15 times as fast outside the ship from your point of view, and 50x as fast at 99% the speed of light, which is 297,000 km/sec, so good luck going that fast.

[businessman07]

Re: time travel

very insightful reach. so does it exist??? and does anybody know how many theorys there are?

[Reach]

Re: time travel

very insightful reach. so does it exist??? and does anybody know how many theorys there are?

Does time dilation exist? Yes, it is real, it's been observed and data fits the time dilation equation einstein came up with, the crazy bastard figured out this stuff DECADES before any of it was testable!

There is only one 'time dilation' theory. There are no theories for time travel.

[businessman07]

Re: time travel

einsteins cool. so that gay movie with the kids and the watches is plausable. I wonder how they tested his equation?

[Reach]

Re: time travel

einsteins cool. so that gay movie with the kids and the watches is plausable. I wonder how they tested his equation?

Not that hard. Put an atomic clock in something that moves at a decent velocity, say the space shuttle, launch it, and then observe the change in time from the clock on the ship and the clock on earth.

http://en.wikipedia.org/wiki/Time_dilation for more info

[trillobyite]

Re: time travel

Not quite trillo. I would define time travel as being able to pass THROUGH time. Understand this - by dilating time (special relativity), you are not traveling through time, but rather along time as things would normally happen. Everything around you would continue to happen as it would, just at a different rate, and then alas, you would arrive at your destination thousands of years in the future as it were, choices made, lives lived, unable to go back because you simply changed the perspective of measuring time pass. You didn't 'time travel'!

If you would define that as time travel then it's defintely possible because time dilation has been observed.

I think that time dilation constitutes time travel then. But my thoughts probably don't matter; do you know of anyone expert in the field who explains exactly what "time travel" really means ? Is it my definition or your definition, or is there no official definition?

[Reach]

Re: time travel

Well, I've never heard of time dilation being called time travel. It's generally defined by science fiction to be the ability to travel through time, which is a seperate entity of time dilation.

If time dilation is time travel then we do it all the time When you get up and walk you are in fact time dilating...lol!

*runs downstairs and tells mom that I just time traveled*

Actually, it was more along the lines of running through the living room yelling out 'im time dilating mutha ****a'

The simple pleasures in life XD

[businessman07]

Re: time travel

Actually, it was more along the lines of running through the living room yelling out 'im time dilating mutha ****a'

The simple pleasures in life XD

I DON'T CARE WHO YOU ARE THATS FUNNY RIGHT THERE!!

[Reach]

Re: time travel

All while reiterating my point! See, it would be silly to define time dilation as time travel because any change in energy /gravitational field causes time dilation.

If you had a clock accurate enough you could indeed measure time dilation by running around, though, it would have to measure something like 20 places past the decimal XD

[sertman]

Re: time travel

I was thinking that maybe time travel is possible if you can't change anything, you can only observe, which led me to an interesting thought (i didn't read the entire topic so if this was said already I apologize)

Does the past really exist? It happened, sure, but does it still exist? Which lead me to this thought: There is no real such thing as the present or the future. The present is always the past. There is no accepted length of time for it to be "right now." As i type right now, my actions are in the past. When you read this, it will be the past. But is there really a present?

[dore]

Re: time travel

The present can't be measured, but it exists, in the same way that a point has no dimension but still exists.

[Samineru]

Re: time travel

Also people are ignoring the fact that if it was not possible to travel through time nothing would happen. So the real question is can we modify the speed of our travel through time. http://www.rebelscience.org/Crackpot...us.htm#Nothing is a relevant article talking about travel through time. But one of the most clear and understandable points to me was how would you measure time travel? Would it be something like 1s per 5s? Then you would simplify to a speed of just 1/5, with no units, which just is not acceptable.

[trillobyite]

Re: time travel

Have any of you seen Stephen King's "The Langoliers"? It deals with this subject, but it seems to hold a view completely opposite to everyone here.

[flamingspinach]

Re: time travel

k. If time is a quasi-spatial dimension of the space-time continuum, as almost everyone seems to agree, then time travel is essentially meaningless within one universe.

First imagine a flat, perhaps square universe. Flat people living on the flat world move around on it. Let's say the lifetime of this universe is 10 minutes. If you looked at the flat square for 10 minutes you'd see everything happening for its lifetime. Now imagine that you took a snapshot of this square universe at infinitesimal intervals and stacked them at infinitesimal distances to each other. Now you'll have a rectangular prism, and if you pull out an infinitely thin slice at any point along the new "depth" you've created you'll have a particular moment of the 10 minutes for which the universe existed. In essence you have created a 3-D space-time continuum, in which two of the dimensions are tangibly spatial (to the people in the continuum) and the third dimension is a "quasi-spatial time dimension". (The third dimension in this case is the dimension along which we "stacked snapshots"). Now you just have to imagine this in four dimensions and you'll have a general idea of what our universe would be like, if we accepted our time dimension as a quasi-spatial dimension.

Now take our flat world again, and imagine only the people on the flat world, extended through "10 minutes" of the third dimension that was added. For simplicity's sake, think of two people shaped like circles. Let's say they just sat there for all of the ten minutes. Then in their 3-D continuum, their "total shape" including their time dimension would look like two cylinders. If over the course of the 10 minutes, the two circles rotated around each other, for example, then their "total shape" including their time dimension would look like a double helix. If the circles bounced off each other, you'd get an "X" shape. You can extend this to more complex motions, obviously. Notice that you can't get something like, for example, an "H" shape (assuming the time dimension is the vertical component of the H), because for that to happen, looking at the tangibly spatial dimensions only, there would suddenly have to be a "bridge" between the two circles for no reason that would then disappear again, breaking what we would consider our "laws of physics". So the cross section of the continuum representing the tangibly spatial dimensions must always contain the same area, if you represent energy as mass as well (which is the first law of thermodynamics). Essentially, the physical laws are simply restrictions on the form of the "total shape" of the sum of the particles in the universe, if you think about it.

When one extends this concept to our own space-time continuum of three tangibly spatial dimensions and one quasi-spatial time dimension, one might say that we all exist in a timeless 4-dimensional instant, along which our consciousness "parses". If you take into account quantum randomness it becomes a bit more complicated but I think the general idea still holds.

So now I think the main problem with the concept of time travel is this: if you "travel back in time", by the conventional meaning of the phrase, your current body and self would simply be transplanted into a previous era. However, that means you are maintaining a continuity of time along your own lifetime which loops back on itself. Since time is a dimension of our existence along which our consciousness travels, this doesn't really make much sense.

Furthermore, if I went back in time from today, 2006-06-12 to, let's say, 1980-04-15, where exactly would I be? What's the reference point? I might be on a different point on the globe, depending on the difference in time of day. Or I might suddenly materialize in space in a part of Earth's orbit that Earth is not currently occupying. Heck, the entire solar system is moving within the galaxy, and the galaxy is moving too, depending on what reference point you're using. If you think of the normal course of events (i.e. without time travel) then it's obvious where you will be, because your position will be relative to where you were before, and the integration of your velocity. But by moving things back in time you sort of are disregarding causality and breaking the physical laws that restrict form of "total shape", as I said before. A simpler consequence of this is also that you're breaking the conservation of mass by moving things to different locations along the "time line" (the quasi-spatial time dimension). But all of this is moot since the universe is a timeless 4-D "instant", because nothing can change in a timeless place unless you add another time dimension along which it changes. Remember that change can only happen over time - the definition of change is a difference between something earlier in "time" and what it "changed to" later on in "time". Once you're looking at time as a direction along which to move, you can't also use it as the reference point for your changes to time (i.e. your putting yourself in it).

I could go on, but there's just a huge number of things that don't make sense about time travel, and that in fact just relegate its very plausibility to an illusion of the mind. There may be a way to accomplish the semblance of "time travel" (i.e. allowing us to interact with something we perceive to be our past) but it doesn't even make sense to say that we can affect our own past.

-fs