Time Travel???

But you age.

My advancing age is only perceived and has no factual essence.

Dumping that "not real" perception sure would be a pain though wouldn't it? Should I canx all my appointments for next week? :p

The sense of the "factual essense" would be doubted but for human perception (of "time" in this case).

Re: Time Travel???


Everything -- everything -- that we know aught of is "only perceived" by us. If I stub my toe, the pain I experience is 'only preceived' by me and by no one else. Does that mean it has no 'factual essence'? Oh, well, I'll just forget about it. It's not real. That car coming straight at me is only something which I perceive. So there's no need to get out of the way. It has no factual essence.

Oh, and welcome to A2K, Axon. You chose to get your baptism of fire with a question that is bound to generate some deeply felt albeit esoteric responses. Good work (and brave).

I suppose what I was thinking about, in terms of 'time travel', is that we cannot possibly travel in time as we would arrive nowhere - the past and the future only exist in our minds. I'm beginning to think it was a stupid, rather than brave topic to post, Merry Andrew! Trying to put my thoughts down like this is a new thing for me, and my head is already starting to hurt! As far as I can grasp it, the mathmaticians tie time up with light, and the speed of it. Hence the ideas of travelling faster than light to go forward in time, and even faster to go backwards in time. But time is surely only a concept for measuring how many times we've been round the sun since, for example, I posted this topic. No, I'm sorry, I'm losing my train of thought already. I think I'm with Einstein on this though. Time is relative - and if you can move forward in time, time moves with you relatively - the idea that you could go forward a couple of years and not age a couple of years holds water, so to speak. But you wouldn't then be able to come back to the point you started at.

Light in the mathmatical sense, is used as a reference because it is something we can use as a universal constant and a tool of measurement. No matter where you travel to in the universe light travels at the same speed (except of course around a black hole but...).

Theories have stated that we'd have to travel faster than the speed of light but no one knows exactly how much faster to create a perceptable shift in time. The speed of light is the "holy grail" of limits because Einstein's theories held that it could never be exceeded.

Just reading something in Scientific American Mag.
I know it's not the definitive vehicle for cutting edge physics but it's valuable to me because of its style and efforts to explain "rocket science" subjects to people like myself.

Seems that if space is constructed of some type of fabric (discreet units woven together) then light with different energies travel at slightly different speeds (blue faster, red slower is a simplistic example). The theory is LQG (Loop Quantum Gravity). So, does this mean Einstein is in error? Well, not yet. But the fact is that Einstein's goal of a unified theory is still alive. Time travel is intriguing but just about every theory that proposes such an event requires extraordinary amounts of energy. Possible? Maybe, but with many caveats. These caveats range from energy requirements to the definition of "time" itself to time expansion and contraction. Kip S. Thorne has expounded on this and comes to some interesting conclusions regarding this subject. Those Star-Trekies might be interested in his discussion of the distinct possibility of teleportation -- definitely possible according with quantum theory, we need only to extrapolate so as to include such action involving more than sub-atomic particles!

JM

Axon, Your original post did not have specific questions. Posts like these are a bit difficult to answer seriously. I try to respond in a way that is serious and will lead to an interesting discussion.

First, we are moving forward in time right now. This is not a problem. Moving backwards is the thing that is difficult.

Second, time is relative. Two people will see different amounts of time pass by for the same event. If there is interest I will post the twin paradox where two twins can get together and realize that one has experienced 12 years while the other has only experienced 10 (even though they were born at the same place and time).

That time is relative is a fact that has been measured in many experiments.

Third, going back in time is theoretically possible (i.e. we don't have any hard and fast scientific rule that says you can't do it).

The problem is it leads to some nasty paradoxes of the form "what happens if you go back and kill your own grandfather. Well then you wouldn't be born ... then you couldn't go back and kill your grandfather ... well then you would be born ... well then you could go back and kill your grandfather ... well then you couldn't...." you get the idea.

Fourth, to a physicist, time is a variable in the equations that describe how the universe works. People with physics training all understand implicitly that any discussion of time is based on the mathemetical laws starting with Newton and going through Hawkings et al. It is sometimes hard to talk about time in a scientific sense without a common understanding of these mathematical laws.

Lemme second what eBrown just said.

The answer to the question: Is time travel possible?...

...is an unqualified "YES!"

I do it all the time. (Pun intended)

And unless you all are just figments of my fertile imagination -- so do all of you.

Can we somehow travel into the past?

We'll in a sense, we do that all the time, too -- each time we go out and look at the night sky.



That other stuff -- I doubt.

eBrown - I certainly would be interested in the Twins Paradox. And I take your point about a common understanding about the mathmatical laws pertaining to this matter. I am afraid to say, I have not studied them, and have only picked up bits and pieces of them through 'popular' science media.

I heard a theory once, though, about using three artificial gravitational devices to literally pull a point in space to where your devices are. One could then, apparently, step inside this point, turn off the devices, and that point would snap back to where it started from with you inside.

Anyone heard of this? If you could use this method to travel vast distances in space instantaneously, would this not, theoretically, make it possible to travel back in time?

Frank, I am becoming more and more sure that I am a product of your fertile imagination!

But does that make me any less real?

Certainly, the earth travels around the sun, etc. regardless of the presence or absence of observers ... thus time exists independent of any of us.

I'd work on this, if I were you. And maybe I am...so get it under control. :wink:




You certainly seem "real" to me...but perhaps I am being deluded by my firtile imagination.

Kevin. This is not correct. The earth does travel around the sun regardless of the observer but this does not mean that time exists independent of any of us.

Let me explain what relativity says (and the sun is a great example).

You and I have a life time of (let's say) 80 years. Assuming you stay on the Earth for the time we are expected to live, we will see the earth travel around the sun 80 times.

But from a different perspective, you will observe a different time. if you are travelling away from the Earth at near the speed of light for 80 years, you will only observe the Earth traveling around the earth *less* than eighty times. You will still have aged 80 years, but the Earth will appear to have aged less.

Here is the twin paradox I promised.

THE TWIN PARADOX

I have two twin nephews Joshua and Malcolm. Joshua is 12 years old, and of course Malcolm is also 12 years old.

If I send Malcolm on a space ship at near the speed of light, the time the experience will be different. Let's say Malcolm is on the spaceship for 10 years. During this "time" Malcolm has experienced 10 years in every conceivable way. His watch has gone around 10 years worth of times, he has aged physically 10 years and he has had time to read 10 years of books, ten years of work etc etc etc.

However in the same "time" Joshua may have experienced *more* time (lets say 15 years). This means that Malcolm will be 22 and Joshua will be 27. Joshua will have experienced 15 year in every conceivable way. He will physically be (and appear) older. His watch will have gone around 15 years worth of times, he will have had time to read 15 years worth of books etc etc etc.


This is what physicists mean when they say that time is not independent of the observer. Each observer will measure time at a different rate. We call this time dilation and it is caused by very high speeds, or by very large masses.

Incidently this theory has been proven over and over. The orbit of Mercury (the first planet) is "slower" than Newton predicts because "time" is slower when viewed from the Earth becuase it is so close to the mass of the Sun.

We have also done experiments that show this effect with clocks on airplanes and particles in accelerators.

If I send Malcolm on a space ship at near the speed of light, the time the experience will be different. Let's say Malcolm is on the spaceship for 10 years. During this "time" Malcolm has experienced 10 years in every conceivable way. His watch has gone around 10 years worth of times, he has aged physically 10 years and he has had time to read 10 years of books, ten years of work etc etc etc.

If Malcolm aged 7 years then he experienced 7 years, and "I" experienced ten years if "I" aged ten years in the meantime.

Axon, I don't think you get it yet. The question is in the type of proof you will accept.

There are many ways to measure the passage of time.

You can rely on a mechanical process with a set speed (i.e. a watch). You can look at biological processes that occur over a fairly regular time schedule (i.e. aging. I can tell the difference between a 20 year old and a 30 year old). You can find something that happens over a regular period of time and count (i.e. atomic clocks or the sun rotating around the earth).

For all of these methods of measuring time, Malcolm will measure less time than Joshua. This has nothing to do with biological clocks or psychology. This is a basic feature of the universe.

It is possible (with speed very close to the speed of light) for Malcolm to be gone for 80 years (that is he will be an old man and will have done the same amount of stuff that a person can do in 80 years), but come back to an Earth that is 1000 years older.

While it is (presently) impossible for a person to live for 1000 years, with very fast travel it would be possible for a person to be on earth after 1000 years. The trick is that while the Earth has experienced 1000 years -- the person only experences 80.

This trick is done on the subatomic level all the time. There are particles that only can live for microseconds. They travel much farther (to us who are watching from Earth) than possible in their "lifetimes" becuase we are watching from our time, but the particles age in theirs.

To understand Relativity (which is what we are discussing) you need to give up the idea that there is a Unversal time that marches along at the same rate for everyone. This universal time does not exist.

The thing you call "time" is completely dependent on your perspective. There is no real time (if real means something that will be measured the same by everyone).

This is very strange. But it is how the Universe works.