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# Time Travel

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my physics teacher in high school told us that if you were to fly around really fast in space then when you came back to earth, everyone on earth would be old, and you would still be young. how is this true?

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Yes, I've heard that too. I don't know the exact explanation, it would be nice if someone could tell us .

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You are currently moving through both space and time. Even when sitting still you are moving extremely fast (The Earth is rotating on it's axis and revolving around the sun. The sun is moving around the Milky Way. Everything is moving away from the centre of the universe). The more movement you dedicate to moving through space (i.e The faster you go), the less you move through time. Therefore, if you move at the speed of light (The fastest speed possible) you will be dedicating ALL your movement in one "direction" through space-time, the "direction" of space. This means that you are not moving through time. This is why photons do not age and why time travel, in the sense of moving at the speed of light (or close to) to get somewhere is theortically possible. So, ironically, time travel can be achieved by not travelling through time.

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Gravity also plays a factor

atomic clocks set one at the top of a mountain (somewhere in the andes? im not sure) and the other at the bottom would have different time after a while, where the one with less gravity would move slower

thus high speed space travel would be ideal

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So, ironically, time travel can be achieved by not travelling through time.

That makes all too much sense.

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Gravity also plays a factor

atomic clocks set one at the top of a mountain (somewhere in the andes? im not sure) and the other at the bottom would have different time after a while, where the one with less gravity would move slower

thus high speed space travel would be ideal

Well, gravity is the bending of space-time and so both space and time are distorted, time more-so then space. Without time, gravity wouldn't work.

The difference in time between a mountain top and say a valley below will be absolutely miniscule but, when applied to extremely large and/or dense bodies, the effects are obvious. Black holes are the best example of this. The matter at the centre of a black hole is so dense that space-time is distorted to the extent that time as we know it would either come to a complete stand still or would be completely different to how we experience it here on Earth.

Edited by PhyschoPotato

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First post in debates yo. I'm not really sure if I should be posting in here, but I was browsing and found this. I was thinking about time-travel earlier.

From what I've figured out, it's impossible to go into the past and see yourself or anybody who knows you. If you did, that person would remember and most likely tell the version of you that they know, thereby creating the memory of your friend meeting your future self, also telling you that sometime in the future you would be travelling into the past. Of course, the "past" would be the present. If this were to happen, it would mean the paths of every single human beings life is predefined. If this occured, how would it be possible for you to come to the moment in time where you "decided" to venture into the past and turn down the oppurtunity, if your future self had already done so?

If you understood any of that, you deserve a cookie.

-Kotsudaira

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Time travel is impossible on so many many levels, The first level would be that someone would have done it, they would have come back from the future wouldnt they? Or into the future?

Physics states we can fly round the world and when we came back etc etc everyone would be older, but theory cant work like that, Unless you had a new spaceship that was found by a time traveler who then tried it and came back in time...Urrggg, now im getting confused!

Anyway theory says you cant do it, Its like yeah, you can shoot an arrow through an apple on someones head but what if you miss?

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Time travel is impossible on so many many levels, The first level would be that someone would have done it, they would have come back from the future wouldnt they? Or into the future?

Physics states we can fly round the world and when we came back etc etc everyone would be older, but theory cant work like that, Unless you had a new spaceship that was found by a time traveler who then tried it and came back in time...Urrggg, now im getting confused!

Anyway theory says you cant do it, Its like yeah, you can shoot an arrow through an apple on someones head but what if you miss?

Time travel doesn't have to be back in time and it doesn't have to be in the common sense of actually travelling through time to some point in the future or past through a wormhole or whatever.

If you were to fly around the world at an incredibly fast speed for a long period of time, everyone on Earth would be experiencing time "normally" and would be ageing at a "normal" rate. You, in your super-fast jet would be travelling through time slower then the people on Earth and would therefore be ageing at a slower pace. Time is extremely difficult to understand fully because we never experience any noticeable change in our path through it. We see it totally wrong from an everyday perspective. Someone can spend eternity (or until the universe is destroyed) caught in a timeless state within a blackhole (Impossible in practice, obviously) while time elswhere continues as normal. Time can be warped, sped up, slowed down. There are fluctuations in time occuring when you drive your car to work, you are travelling through time slower then someone walking along the pavement outside your window it's just such an incredibly small difference that you won't notice it.

While this is theory it has been backed up by the use of extremely accurate atomic clocks on board high-speed jets. The time on the clocks from the planes has been compared with clocks on the ground and there has been a difference, a tiny difference but a difference nonetheless. Obviously it is an integral part of general relativity as well. A theory that has proven to be hugely accurate when subject to hundreds of various experiments.

Edited by PhyschoPotato

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So, Time would move normally for you, But because your going around the Milkway at high speeds, Earth would have done several years, by the time you done like an hour?

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So, Time would move normally for you, But because your going around the Milkway at high speeds, Earth would have done several years, by the time you done like an hour?

To be honest, I'm not sure what time would be like if you were to travel at near light speeds, I suppose due to everything working slower (including your brain) you would experience it as normal. If you were to travel at these speeds then yes, you would experience and age say, 1 month whereas everyone on Earth would experience and age a few times that. If you were moving at the exact speed of light you wouldn't experience time at all, you wouldn't be moving through it and therefore wouldn't experience it or age.

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As long as your velocity was constant, you wouldn't even realize you were moving. Your sensation of time passing wouldn't be any different, you'd just find that time passed much more quickly for people who weren't travelling as fast. Like... right now you can't really feel it, but you're moving quite a few thousand miles per hour through space. But since the earth and everything else on it is moving in the same direction at that same speed, you don't feel a thing.

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Hold on, wormholes doesn't travel you through time, wormholes just travels you the another point in space.

Extremely fast.

Travelling back in time is of course impossible.

But travelling forward is what we are doing right now.

But in case you want to go faster than that, you might need to build a super fast space ship and get out flying.

This is basic of Einstein's relativity theory.

Let me allow to explain the theory:

Imagine a train moving at 40 km/h on tracks. One person is sitting on the 4th most left window ( out of a maxium of 10 windows on the train ).

Another person is standing on the site of the tracks and looking towards the tracks.

Since the first person ( A ) is not placed in the center of the train, the second person ( B ) would be able to look at the middle of train without looking at A.

So here it is, when the train's center is precisly where B stands, two lightings strucks at each end of the train, because of the movement of light they meet B at the same time, which gives B the opinion that the lightings struck att the same time.

However, because of A's placement a bit back in the train and at the same time the movement of the train, A will move into the light of the front lighting first followed by the back lighthing, which would give A the opinion that the lighting on the front struck first.

Also, there is another way to put it.

You're standing on a moving object that moves 15 km/h, ahead of you is another object moving 12 km/h, but for you it looks like it's moving 3km/h towards you, whilest the whole world around you seem to move at 15km/h towards you, and also while the object you stand on seems to move 0km/h.

However, a person standing watching would see both objects moving respectively 15km/h and 12km/h.

So speed is a relative form, as it can be different from point of view.

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Yay, a science lesson from Svip . He is 100% correct though, or well Einstein is atleast.

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Yay, a science lesson from Svip . He is 100% correct though, or well Einstein is atleast.

Wow.

It took you one minute to read that?

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I must admit that this is all beyond me.

I don't quite understand how objects know what they're supposed to be moving in relation to.

Examples:

1. You're on a train moving at the speed of light (yeah, it's a supertrain) away from earth, and you move at four miles per hour from the back to the front. According to einsteins theory, you're not moving 4mph faster than light, you're just moving 4mph relative to the train. But isn't that just a copout? Aren't you moving 4mph faster than the speed of light away from (or relative to) the earth?

2. The train has headlights, light moves at (you guessed it) the speed of light, but so is the train, so option one is that the light can't leave the front of the train, because it's already traveling as fast as anything can go (relative to the earth), which would indicate that nothing can travel faster than light, and einstein was correct.

Option 2 is that the light somehow knows that it's movement is relative to the train and not the earth, so it can travel away from the front of the train, but then if the train stops, isn't the light moving forward away from the train and the earth at two times the speed of light?

3. Relatively speaking (ha, a pun) I am sitting still, but the earth is spinning at something like 27,000mph (I think, I'm could be wrong but I have no way to measure it.) it's also orbiting around the sun at some high speed, and (since the universe is expanding) it's also travelling away from the center of the universe.

What if somewhere out there, on the exact opposite side of the universe (outwards from the center), there is a guy sitting still on a planet. And this planet at some point in it's orbit, and at certain points in it's rotation, is moving in the exact opposite direction as us, in addition to expanding away from the center of the universe. How is it possible that if he's moving faster than the speed of light relative to me, that he really isn't, we just aren't allowed to relate our speeds to each other?

Sorry for my stupidity, but I have a hard time grasping this.

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No.

If you are on a train that moves the speed of light, and you start move towards the front at 4 km/h, you are moving relative to the Earth 4km/h faster than light.

But within the train everything seems to stand still, so you just moving 4km/h relative to the train.

As for the light on the front, the light enters the vacuum of space ( which I would guess since you are travelling at the speed of light ), and since in space, the speed of the light is not relative to the train, but rather to space, which would not allow the frontlights to move faster than the train.

However, if you turn on a flash light within the train, it would light as it should, since within the train it's relative to the train.

For instance, even though you say you're travelling at 50 km/h down the road in a city, you are only travelling at 50 km/h relative to the Earth, but to space you are travelling much faster.

So question is, if the speed of light is different towards the Earth and space.

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As for the light on the front, the light enters the vacuum of space ( which I would guess since you are travelling at the speed of light ), and since in space, the speed of the light is not relative to the train, but rather to space, which would not allow the frontlights to move faster than the train.

However, if you turn on a flash light within the train, it would light as it should, since within the train it's relative to the train.

Light is relative to anything and everything. You are in the train, looking at the light coming from the headlights and so you would see it as a beam of light. It doesn't matter whether it's in the train or not light always moves at 670 million miles per hour relative to whatever you choose, in this case, the train.

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What if somewhere out there, on the exact opposite side of the universe (outwards from the center), there is a guy sitting still on a planet. And this planet at some point in it's orbit, and at certain points in it's rotation, is moving in the exact opposite direction as us, in addition to expanding away from the center of the universe. How is it possible that if he's moving faster than the speed of light relative to me, that he really isn't, we just aren't allowed to relate our speeds to each other?

Sorry for my stupidity, but I have a hard time grasping this.

It is impossible to move faster the light. Relative to anything. It simply isn't going to happen.

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I have no freaking idea what Svip ment bout the Train way of puttin it, But i got the 2 moving objects 1 alright...

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What if somewhere out there, on the exact opposite side of the universe (outwards from the center), there is a guy sitting still on a planet. And this planet at some point in it's orbit, and at certain points in it's rotation, is moving in the exact opposite direction as us, in addition to expanding away from the center of the universe. How is it possible that if he's moving faster than the speed of light relative to me, that he really isn't, we just aren't allowed to relate our speeds to each other?

Sorry for my stupidity, but I have a hard time grasping this.

It is impossible to move faster the light. Relative to anything. It simply isn't going to happen.

Okay, now I'm really confused.

I found this.

"Is the universe expanding faster than the speed of light?" They said the answer is yes and no, some things do move faster than light in relation to each other, sort of. They are slightly ambiguous about it, but that isn't even my point.

What I was actually asking was, how would/does the universe, or the laws of physics, or whatever you want to call it, (Using question 3 from my other post.) know that I am going at speed a specific speed, and the other person is going at a specific speed, and right before our speeds (Relative to each other.) are about to total a number even slightly faster than the speed of light, that it's time to stop or slow down one of us? And how would it go about doing that?

Meaning if 299,792,458 meters per second is light speed, and somehow object A (Some sort of imaginary super-rocket) could actually reach a speed of 149,896,229.5 (.5 meters per second faster than half of light speed) and object B could do the same (Yes it has an imaginary sister-rocket.) and they both were shot into the exact opposite direction, how would the universe/laws of physics stop or slow one of them down? Because if neither of them are slowed, then their speed relative to each other would be 1 meter per second faster than light?

I'm not trying to be a hardass, I really just don't understand how something like that could possibly happen.

My source for light speed since I only knew it in miles.

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What if somewhere out there, on the exact opposite side of the universe (outwards from the center), there is a guy sitting still on a planet. And this planet at some point in it's orbit, and at certain points in it's rotation, is moving in the exact opposite direction as us, in addition to expanding away from the center of the universe. How is it possible that if he's moving faster than the speed of light relative to me, that he really isn't, we just aren't allowed to relate our speeds to each other?

Sorry for my stupidity, but I have a hard time grasping this.

It is impossible to move faster the light. Relative to anything. It simply isn't going to happen.

Plus the G forces would leave you like a puddle before you even reached a tenth of that speed, so unless we can work out how to circumvent that, we'll not be able to do it.

Also, this theory doesn't allow time travel as such in the way that Waddy is chewing over, it's simply traveling faster through time.

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Okay, now I'm really confused.

I found this.

"Is the universe expanding faster than the speed of light?" They said the answer is yes and no, some things do move faster than light in relation to each other, sort of. They are slightly ambiguous about it, but that isn't even my point.

It's dodgy ground. When we talk about the speed of light in reference to local objects, it is absolutely impossible to exceed light speed. What you are talking about is 2 extremely distant bodies moving away from each other on opposite sides of the universe. This works in a different way to normal, local objects. They are moving so fast due to the expansion of the universe, which is the stretching of space. These objects therefore aren't actually moving at light speed in the way of just rotating around their local star at light speed, or whatever, they are effectively being moved by space stretching.

What I was actually asking was, how would/does the universe, or the laws of physics, or whatever you want to call it, (Using question 3 from my other post.) know that I am going at speed a specific speed, and the other person is going at a specific speed, and right before our speeds (Relative to each other.) are about to total a number even slightly faster than the speed of light, that it's time to stop or slow down one of us? And how would it go about doing that?

The universe doesn't have to enforce a maximum speed limit in that way. To travel at the speed of light a particle needs to have a rest mass of 0, so anything that has weight will stationary can not reach light speed. This is because the mass of the particle will increase with speed until it finally reaches light speed and becomes infinity times heavier. Anything with a rest mass greater then 0 would become infinite in mass and this is not going to happen. Particles with 0 rest mass (photons) can travel at the speed of light because 0*∞ still equals 0.

Meaning if 299,792,458 meters per second is light speed, and somehow object A (Some sort of imaginary super-rocket) could actually reach a speed of 149,896,229.5 (.5 meters per second faster than half of light speed) and object B could do the same (Yes it has an imaginary sister-rocket.) and they both were shot into the exact opposite direction, how would the universe/laws of physics stop or slow one of them down? Because if neither of them are slowed, then their speed relative to each other would be 1 meter per second faster than light?

This is more complex. I'm going to phrase it this way: There is a rocket travelling at 1 m/s less then the speed of light and someone rolls a ball from the back of the rocket to the front at 2 m/s. This would give the picture that, relative to a stationary outside observer, the ball is moving at 1 m/s faster then light. This type of question can only be answered using Speed dialation which uses this forumla:

Speed of the rocket relative to you = v

Speed of the ball relative to the passengers = b

Speed of the ball relative to you = y

Speed of light = c

y = (b+v)/(v*b/c*c+1)

This forumla works in close conjuction with length contraction, time dilation, time shift and mass increase. Without just one, the others can be proved wrong but when used together they are extremely accurate. So to understand this fully you may wish to read up on these other basic formulas of general relativity.

I can't think of a way to simplify this as it's pretty complicated but it is a key part of general relativity and so for Einstein to be correct, this formula and what it implies must also be right.

Edited by PhyschoPotato

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I'm not that smart but maybe you guys can correct me on my theory and teach me something.

Say you are travelling at a very far away star on Earth. Since it takes millions of years for the light to reach Earth, you are viewing the star a million years ago. You hop in your super fast spaceship and fly towards the star. You are travelling so fast that the you are viewing all the activities the star has gone thru throughout all those years. So now your near the star and it is different. You have now caught up to its present day form from your point of view. So from Earth, travelling outwards to a light source is speeding up the changes from your perspective. Therefore, in a way you are traveling to that star's time.

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I'm not that smart but maybe you guys can correct me on my theory and teach me something.

Say you are travelling at a very far away star on Earth. Since it takes millions of years for the light to reach Earth, you are viewing the star a million years ago. You hop in your super fast spaceship and fly towards the star. You are travelling so fast that the you are viewing all the activities the star has gone thru throughout all those years. So now your near the star and it is different. You have now caught up to its present day form from your point of view. So from Earth, travelling outwards to a light source is speeding up the changes from your perspective. Therefore, in a way you are traveling to that star's time.

You are just moving through the light that the star is emitting. Slowly you will come nearer and nearer to the source and so the light will be more "new" and you will eventually see it's light from only a few minutes ago. This isn't travelling through time in the way you're thinking of. We can look at galaxies and see them as they were millions of years ago but that doesn't mean we've travelled x million years back through time, it's just how long the light has taken to reach us.

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I wrote an exam about these theories; about the lightyears and the actual speed of light that makes time travel possible... So, I fully understand what you have written in here to this moment. What I wonder about is time travel where you don't actually move through the universe but back in time. Like when I want to "travel" back to the 50s or something the like. How would that be possible?

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I know what you mean by the light taking time to reach us. Like the sun takes 7 minutes or so, but what I mean is it is like your traveling to speed up from your point of view what happened to that star, not the whole universe.

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I wrote an exam about these theories; about the lightyears and the actual speed of light that makes time travel possible... So, I fully understand what you have written in here to this moment. What I wonder about is time travel where you don't actually move through the universe but back in time. Like when I want to "travel" back to the 50s or something the like. How would that be possible?

It wont.

Travelling back in time is impossible, it might be possible travelling ahead, but back is impossible.

@GTAFool12;

Imagine this; you are travelling your rocket, train whatever, at the speed of light, even though such physics as G doesn't allow you to live in such condistions, nor does the rocket allow itself to move at that speed, since it will be at any rate ripped apart.

But it's theory now, so you are. While travelling you look at the star far far away, and as you get closer you get a newer information, but in realitity, you just get them twice as fast as you would on Earth, since Earth is standing still, they are gained with the speed of light. But since you are moving at speed of light towards the star, you are getting those pictures twice the speed of light, which just mean you get the twice as fast as on Earth.

As you reach the star, it will have taken the same time as it's pictures got send to Earth, meaning that you have not travelled into another era, but rather just along time.

However, personally I don't believe in travelling in time at all, not even ahead.

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I wrote an exam about these theories; about the lightyears and the actual speed of light that makes time travel possible... So, I fully understand what you have written in here to this moment. What I wonder about is time travel where you don't actually move through the universe but back in time. Like when I want to "travel" back to the 50s or something the like. How would that be possible?

It wouldn't be possible. At least not with our current understanding of the universe and that's an understanding that has proven to be very accurate.

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Exactly what I thought.

Back to time traveling by space and the speed of the light; it's is possible but humans can't endure light speeds. If that would be possible, it can be done. But you need to find the right technology to make it possible.

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