Thread: Looking at time travel in the simplest way possible

At every point, matter and energy takes up a spot somewhere in the universe right?
Time is simply the speed at which matter and energy change position or form, still right?

Therefore only the PRESENT exist.

Just because we have memory we can imagine the past and the future.
However, if energy cannot be created or destroyed, this means the matter and energy in space can only exist in ONE PLACE at ONE TIME.

I always found the concept of time travel ridicolous because it sounds this simple.

What am i missing?

Edit:Typos

Originally Posted by Raziell

Therefore only the PRESENT exist.

Like an infinite now. Yes, I've had similar thoughts. Past and Future always included in the present.

Here's where it gets sticky. Your now and my now are different. We have different frames of reference, and experience different "nows."

Further, "now" is never realized since it's always passing before being realized... as it gets replaced by the future.

This might be more of a philosophical thread... at least, I know my response is not physics. Cheers.


iNow

Time is relative to speed and thats where things get complicated. If i was to travel at the speed of light nothing would change thus time would stand still but not for me. I would still age, move freely and what not.

Other than that i cant really tell you much more other than to travel at the speed of light (or faster) you need an infinite amount of energy.

Time travel is most likely impossible. There is currently no reason to believe that it should be possible; the idea therefore should be kept out of mainstream science and only left in sci-fi.

All of the ideas out there of multiple universes and whatnot to explain time travel have been forced and did not come about naturally, so they should be ignored. The closest thing we will ever have to time travel is 'time dilation', but that is simply time being slowed down for the object, not reversed.

True time travel would involve every bit of matter and energy in the universe having its form changed to a future or past state. Sound hard? It is. So hard we might as well declare it as impossible until we have advanced scientific knowledge for another 10,000 years....but oh, THAT'S RIGHT, we will destroy ourselves by that point like we have time and time again. Oh well, no time travel then I guess : /

Originally Posted by Cold Fusion

Time travel is most likely impossible. There is currently no reason to believe that it should be possible; the idea therefore should be kept out of mainstream science and only left in sci-fi.

All of the ideas out there of multiple universes and whatnot to explain time travel have been forced and did not come about naturally, so they should be ignored...

There was a time when going to the Moon was thought "most likely impossible"...

Personally, I wouldn't exclude as many ideas from science as you're suggesting. It's true that a lot of people propose "theories" that are so poorly thought out that they're ridiculous. Bad theories don't make the subject matter itself unworthy of consideration, though.

Chris

Originally Posted by Cold Fusion

Time travel is most likely impossible. There is currently no reason to believe that it should be possible; the idea therefore should be kept out of mainstream science and only left in sci-fi.

Time travel can be equated with the existence of closed timelike curves (CTCs)in general relativity.

It is known that there are solutions of the Einstein field equations, spacetimes, that admit CTCs. But those solutions are a bit contrived.

It was proved by Hawking that spacetimes that obey the weak eneergy condition do not admit CTCs. That theorem is one step in the proof of what Hawking has called the "Chronology Protection Conjecture" -- that CTCs cannot exist in the real world. But this conjecture is only a conjecture so far.

So, "time travel" is a legitimate scientific topic, IF it is treated scientifically. But, to treat it scientifically takes a deep understanding of general relativity. You are not likely to see a discussion in this forum predicated on a sufficiently deep understanding of GR.

http://en.wikipedia.org/wiki/Closed_timelike_curve

http://www.its.caltech.edu/~kip/scri...rves-II121.pdf

Originally Posted by Cold Fusion

All of the ideas out there of multiple universes and whatnot to explain time travel have been forced and did not come about naturally, so they should be ignored. The closest thing we will ever have to time travel is 'time dilation', but that is simply time being slowed down for the object, not reversed.

True time travel would involve every bit of matter and energy in the universe having its form changed to a future or past state. Sound hard? It is. So hard we might as well declare it as impossible until we have advanced scientific knowledge for another 10,000 years....but oh, THAT'S RIGHT, we will destroy ourselves by that point like we have time and time again. Oh well, no time travel then I guess : /

You have gone too far.

Originally Posted by inow

Originally Posted by Raziell

Therefore only the PRESENT exist.

Like an infinite now. Yes, I've had similar thoughts. Past and Future always included in the present.

Here's where it gets sticky. Your now and my now are different. We have different frames of reference, and experience different "nows."

Further, "now" is never realized since it's always passing before being realized... as it gets replaced by the future.

This might be more of a philosophical thread... at least, I know my response is not physics. Cheers.


iNow

Your now and my now and not different. We both share a common universe which exists as it does now. The fact that we have a different frame of reference has no effect on that.

Now can also be realised, because everything you do is in the now so there's no other way it could possibly be realised.

Your now and my now and not different. We both share a common universe which exists as it does now. The fact that we have a different frame of reference has no effect on that.

It's true that we live in a common universe, however thinking that spacetime is merely euclidean is a wrong concept.
Think of spacetime as rather being a unity, being Lorentz-invariant
(which means that (ds)² = c²(dt)²-[(dx)²+(dy)²+(dz)²] is the same in EVERY frame of reference - in contrary to the notion of Gaussian translation).

I hope I have used the correct expression.

Now spacetime can be entangled or being curved - by energy and mass (which are equivalent things considering Einstein's equation E=mc²).

And that's where it gets interesting and most probably beyond imagination. :wink:

It is true that we live only in the "present", in the here and now, but it is unclear for many of us how spacetime exactly looks like.

Take a sheet of paper and draw some inhabitants of a 2d universe on it. We see their universe as they do, x and y dimensions which they can move along.
If we now add a time axis in the vertical or z dimension, by moving the paper upwards, we draw out a square column, with lines running up through it denotng the motion of these 'inhabitants' of 2d world through space and time. This square column is their 'Minkowsky' space/time between time=floor and time=ceiling.
At any plane of their upward motion all the 2d world inhabitants can see is their 2d sheet of paper. It is their 'now'. We on the other hand, being higher dimensional, can see their world line going up through the square column from time =floor to time=ceiling, wether it is straight implying no motion or spiralling/winding if motive.

Now extrapolate this to three dimensions with time. Similarily we, being 3d in nature, can only see our now, the 3d foliation (as DrR would say) of the 4d space/time manifold. A higher dimensional being, on the other hand would be able to 'see' our whole world line, fron the past to the future, as it wind through a 4d manifold.

Originally Posted by MigL

Now extrapolate this to three dimensions with time. Similarily we, being 3d in nature, can only see our now, the 3d foliation (as DrR would say) of the 4d space/time manifold.

What you are talking about is one leaf of the foliation -- a Cauchy surface in this case.

But you have the general idea.

Waveman28
Just to tell you your and my now are completely different Einstein even proved that there is no present moment throughout the universe And by the way good on you inow

I am reposting this post I wrote in another thread of a similar nature ( "What is the simplest definition for time ?" ) :

For a given connected manifold with metric g we define



thus



and therefore



which defines the "distance in time" between two arbitrary events A and B.

As for the small matter of time travel, I would generally agree with DrRocket - closed time-like curves will, in my mind, never be observed. I do not doubt that they might exist under some very exotic conditions ( see "Kerr-Metric" ), but I would think they will either be hidden away behind event horizons, or not be causally connected to the rest of the universe in some other way. It's pretty much a no-go, I would say...unless of course you live in a Goedel universe, in which case you can see yourself at an earlier time, if you look in the right direction, and where each event is in fact part of a closed time-like curve...isn't GR fun to play with

to me, the only point where you can speak of a real now is anything prior the Big Bang(the source). any point past that is either the past, relative now, or future.

Originally Posted by Bad monkey

Waveman28
Just to tell you your and my now are completely different Einstein even proved that there is no present moment throughout the universe And by the way good on you inow

And as proof of this, Waveman's now was dated February 27th, 2011, while Bad Monkey's now is dated January 29th, 2012.

I travel into the future and peer into the past every day. Funny though, looking towards where I'm going to be and realizing I'm seeing it as it was. The past seems like the future in some strange way.

Any discussion of time isonly confused when a space related reference of distance is used. As time is aquantification of a transition period between events. You have aptly used avalid concept of the observance of time and that the transition between the occurrenceof two events is a focus. An initial event marks the beginning of the sequence,the sequence moves forward to the next event. Time itself is the quantificationof the transition period between the events of reference. As the transitionperiod increments in a forward direction, the initial event marks the beginningof the observation and the event that follows sets the period. And now is theincrement along the transition period which has just occurred..

Time isthe quantification of the transition period between events. Once the occurrenceof a point in time takes place it is lost as the transition period of thesequence of events moves forward, and replaced that point in time by the next occurrenceof a quantification that marks the sequence. An event in time can be recorded,but it cannot occur more than once. This eliminates any possibility to go backin time.

So when I look at an object then I am observing it through a succession of nows? My nows being the present and the object being observed having its past nows shown to me as if a movie?

Originally Posted by zinjanthropos

So when I look at an object then I am observing it through a succession of nows? My nows being the present and the object being observed having its past nows shown to me as if a movie?

basically and vise versa. the observed object will see you as being the movie.

Does a blind person experience time differently? How would time be sensed if the senses were disabled?

everyone experiences time differently, i.e. when you're happy/in a hurry/in good company, it feels like time flies by.
when you're waiting/bored/bad company, it feels like time slows down.

and without senses you maybe won't experience time, but your body still depends on it, like needing food to function or letting said food out again.

Some years ago a writer named Charles Williams played with the notion of time travel. He reasoned that every atom has someplace it is supposed to be at every moment. Therefore if you could travel in time you are limited to the time you are alive. If you go back too far you just make yourself not yet existstent, if you go too far forward you are just dead. If you go forward to a time within your lifetime you just find yourself living with a parcel of false memories of time you did not actually live through. ( Not that you could tell that they were false.) The worst case is if you travel backward to a point in your own life. You are then caught in a loop and nothing short of devine intervention can save you.

Ancient though they may be, I like how these two posts come together to explain the possibility of time travel.

Originally Posted by Raziell

At every point, matter and energy takes up a spot somewhere in the universe right?
Time is simply the speed at which matter and energy change position or form, still right?

Therefore only the PRESENT exist.

Just because we have memory we can imagine the past and the future.
However, if energy cannot be created or destroyed, this means the matter and energy in space can only exist in ONE PLACE at ONE TIME.

I always found the concept of time travel ridicolous because it sounds this simple.

What am i missing?

Edit:Typos

Originally Posted by inow

Originally Posted by Raziell

Therefore only the PRESENT exist.

Like an infinite now. Yes, I've had similar thoughts. Past and Future always included in the present.

Here's where it gets sticky. Your now and my now are different. We have different frames of reference, and experience different "nows."

Further, "now" is never realized since it's always passing before being realized... as it gets replaced by the future.

This might be more of a philosophical thread... at least, I know my response is not physics. Cheers.


iNow

Suppose we consider your past and future to be part of "you". You can't contradict your own present. You can't contradict your own future. (and so.... it stands to reason that you also can't contradict your own past.)

Also, you only get one chance to decide your future, and one chance to decide your present (and so..... probably you only get one chance to decide your past also.)

However, what about the parts of the past you haven't decided yet? You've already built on the platform of your birth, so no changing that, but what about some unknown guy living in Bangladesh 200 years ago? Have you built on that platform yet? Maybe. Maybe not. I don't see any reason why his past can't be your present or future. Instead of looking for exotic situations, like a whole different universe, why not just look for causally isolated sections of our own universe, and treat those as being the only destinations to which a time machine would have the potential to take you?

Hmm... Have any of you heard about the Philadelphia Experiment? It's still regarded as a Hoax but It does seem to be where this conversation is heading.

Philadelphia Experiment - Wikipedia, the free encyclopedia

Time is nothing more than the measurement of relative rates of change, and though some changes can be reversed, to actually go back in time it would first be necessary to find a means to halt all processes in the Universe and then successfully apply sufficient force to reverse them throughout the cosmos. Even such an extraordinary procedure would not reverse the course of time. Whatever process was engaged to controvert time would also have to CEASE acting at the same temporal point it began, because if it progressed, so would time.

On the other hand, it is easy to travel - and even accellerate - into the future. You do it once a day. It is called sleep. While you sleep, your internal metabolism slows down. When your internal rate of change slows relative to your surroundings, time passes more quickly and hours seems to fly by in mere minutes. If you slow down, the ambient relative rate of change in the Universe speeds up.

Originally Posted by THoR

Time is nothing more than the measurement of relative rates of change, and though some changes can be reversed, to actually go back in time it would first be necessary to find a means to halt all processes in the Universe and then successfully apply sufficient force to reverse them throughout the cosmos. Even such an extraordinary procedure would not reverse the course of time. Whatever process was engaged to controvert time would also have to CEASE acting at the same temporal point it began, because if it progressed, so would time.

.

Not in all the universe just in your ara , thanks

Originally Posted by Cold Fusion

Time travel is most likely impossible. There is currently no reason to believe that it should be possible; the idea therefore should be kept out of mainstream science and only left in sci-fi.

All of the ideas out there of multiple universes and whatnot to explain time travel have been forced and did not come about naturally, so they should be ignored. The closest thing we will ever have to time travel is 'time dilation', but that is simply time being slowed down for the object, not reversed.

True time travel would involve every bit of matter and energy in the universe having its form changed to a future or past state. Sound hard? It is. So hard we might as well declare it as impossible until we have advanced scientific knowledge for another 10,000 years....but oh, THAT'S RIGHT, we will destroy ourselves by that point like we have time and time again. Oh well, no time travel then I guess : /

Any thing that this universe holds, every possibility may be true until & unless it is totally discarded by a scientific law.
I think we should wait.

I guess that by wait you mean slow down time. That has been discussed as dialation of time. The concept of time is a measurement of the duration between the sequence of events as they occur. The key here is "legitimate". Just because time travel can be perceived does not make it legitimate. And to say that we will wait for the scientist to tell us what to think is a joke. For they now tell us such things as Plate Tectonics, evolution, and Relativity. These issues are far from being resolved. I will take my free mind and make the best determination of truth that I am capable of doing. And it is that determination of truth that I will follow. This is part of our free will, to follow that which is our own belief. I give up my free will to nobody, and recommend that no-one else give up their free will.

Fight to hold on to you free will. Once reliqueshed, you will never get it back.

Originally Posted by Jack1941

And to say that we will wait for the scientist to tell us what to think is a joke. For they now tell us such things as Plate Tectonics, evolution, and Relativity. These issues are far from being resolved.

This is true in your universe: the universe where you have the exercised your free will to remain ignorant, uninformed, misguided and mistaken. Such abuse of free will gives freedom in general a bad name. The joke is on you.

To actually go back in time it would be necessary to find a means to halt all processes in the Universe and then successfully apply sufficient force to reverse them throughout the cosmos. Even such an extraordinary procedure would not reverse the course of time. Whatever process was engaged to controvert time would also have to CEASE acting at the same temporal point it began - for if it progressed, so would time.