time travel ?

[The Antikythera Mechanism]

How does that work?

If you spend twenty years travelling and come back to earth, you will be twenty years older, so would everyone on earth.

Surely the only relevance "travelling at the speed of light" has in this scenario is that you would cover a lot of distance. More than you would if you spent 20 years travelling at 60mph, for instance.

Einsteins Theory of Relativity

 

[Danny-Boy]

But thinking about it, if I hopped in a time machine, spoke to someone in say, 1960 and said hello I'm from the future da de da, they'd say what you chatting about, this in 1960 the future hasn't happened yet.... ?

But if you told them St Paddy was going to win the Derby, then they might be interested...assuming you beamed down before Derby day of course.

 

[Acker79]

Isn't it to do with parallel universe theories or summat? I.e. if time travel was possible, we would be travelling back in time to parallel universes rather than this one.

I won't lie, my brain just hurts when I think about this sort of stuff.

There are multiple theories that I'm aware of.

With bill and ted, there was a kinda determined future sense. Things happened because bill and ted would make them happen. There is one time line, and it is followed by all versions. (They plan to, when they complete their assignment go back to steal their dad's keys, the forgetting to wind their watch, etc. (This does somewhat take away free will, though)

One other is the back to the future (part 2) version where you create alternate time lines when you go back, causing multiple parallel universes where each decision causes the birth of a new universe.

 

[Acker79]

Einsteins Theory of Relativity

I'm not overly familiar with the details, could you explain it in this context?

 

[Kalimantan Gull]

How does that work?

If you spend twenty years travelling and come back to earth, you will be twenty years older, so would everyone on earth.

Surely the only relevance "travelling at the speed of light" has in this scenario is that you would cover a lot of distance. More than you would if you spent 20 years travelling at 60mph, for instance.

It does work, I'm afraid

The faster you travel, the slower time passes. At the fastest possible speed time slows to almost zero. The example I use here is known as the 'twins paradox', i.e. two twins, one on earth and one in a spaceship end up being 20 years apart in age.

This is because everything in the universe always travels exactly at light speed, including you reading this post right now, your computer, and so on. Special relativity declares a law for all motion, namely that the combined speed of any object’s motion through space and it’s motion though time is always precisely equal to the speed of light. Adding the total movement through both space and time always equals light speed. Always. Since you must travel constantly at exactly the speed of light, when you increase your speed through space, you decrease your speed through time. When we are not moving we travel through time only, but when we speed up, time slows down.

They've actually proved this using atomic clocks, super-accurate devices that tell time to a billionth of a second or thereabouts. Set them to the same time, leave one on the ground and fly one around the world on a jet plane a few times. Hey presto, the one on the earth is a couple of nano-seconds faster at the end.

 

[Kalimantan Gull]

If an astronaut was traveling close to the speed of light and he traveled for one year according to his watch before returning to Earth, he would return to find that close to 1300 years had passed on Earth.

True (if your sums are right), I meant if the person travelled at the speed of light for 20 earth years, not 20 of his years. He would of course age 20 years if travelling at the speed of light for 20 years.

To paraphrase Einstein, 'its all relative'

 

[The Antikythera Mechanism]

I'm not overly familiar with the details, could you explain it in this context?

Copied and Pasted -

Time Dilation --- traveling close to the speed of light

This is where you have to expand your thinking somewhat. When it comes to the effects of traveling close to the speed of light, it sometimes appears to be mind-boggling when you hear some of the theories that talk about time travel and traveling the great, great distances to the stars in our galaxy and even more so to the other galaxies in the universe. The effects it has on the space travelers and to the people watching them on their home planet is something out of a science fiction novel. It is also true.

I’m going to try and make this as simple as possible because this can make you question what is and isn’t reality. I would guess with the speed of light, it’s a subject most have a hard time understanding because it is out there and it’s sometimes hard just to get your brain to go there, to be able to picture what these theories are implying. These are almost like brain exercises as you try to picture their concepts. It sometimes just leaves you saying, huh? Go back and read the paragraph again if you have to. Once you get it, you’ll find this isn’t all that hard to understand and the next thing will be a little easier until everything will start making sense. There’s one thing about the universe, it follows a strict set of rules, the “rules of nature” if you will. Something happens in our universe because something else happened to make that something happen. Got that? But it’s true. The universe is the way it is today because of all the different things that happened since the Big Bang roughly 14 billion years ago leading up to today. Everything happens because it had to happen.

I’ll begin with part of Einstein’s “Theory of Relativity.” One of the things this theory states is that “time” is relative to ones motion and also to the amount of gravity exerted on one. This is the theory everyone has heard. It says that the faster you travel, the more time slows for the traveler. This is true but only a part of the story. What does this mean? Let me give you an example. This is slightly different than the original but it represents a good example of two people seeing the same thing but with two different perspectives to what each is seeing. It was written by Steven Hawkings in his book “ A Briefer history of Time.” It is a great analogy of where your thinking has to go to understand what I’ll be talking about in a few paragraphs so I’ll use it again and thank the original writer.

It begins, there are two people. One (Bill), is standing on the platform of a railroad station waiting for the train to pull in. The other, Mary, is on a train coming towards the train station. The only thing abnormal about this scene is that the train on one side, the side facing the platform, is missing its side but only to anyone on the outside of the train. People on the outside of the train can see into one side of the train because that one side seems to be missing its wall, but if you’re inside the train it seems like the wall is there and you can’t see outside. I know it sounds weird but just follow me because we need it to be that way but it doesn’t have much to do with what we’ll be talking about. So again Bill on the platform can see into the train but Mary inside the train cannot see out. That’s easy enough. Now inside the train, Mary is sitting on a chair in the center of the train, against the wall on the side opposite of the train platform where Bill is standing and she is facing the platform side. As she sits, Mary is watching two people play ping pong on a table in the center of the train car. Looking at the train the player towards the back of the train is about to serve the ball towards his opponent on the side of the table towards the front of the train. He is serving in the direction the train is moving. At the same time he makes his first serve, the train is passing the train station platform. The train is moving at a speed of 90 miles an hour and traveling past the train station going to the next station.

Now as the train passes Bill on the platform, his eye catches the ping pong game so both he and Mary are watching the player make his first serve. Here comes the strange part of who, what, where and when. When the player hits the ball, the ball will be moving 10 miles an hour in the direction the train is moving. As Mary watches the player hit the ball, she sees the ball move towards his opponent at a speed of 10 miles an hour. Because Mary is traveling inside the train at the trains speed, she sees the ball hit and move at 10 miles an hour. As Bill watches standing on the platform, the train is wizzing by him at 90 miles an hour. When the ball is hit he sees the ball move at 100 miles an hour because he not only sees the ball move at 10 miles an hour, he also sees the train moving at 90 miles an hour so it appears to him that the ball is traveling 100 miles an hour. Which one is right, Mary who sees the ball move at 10 miles an hour or Bill who sees the ball move at 100 miles an hour. The answer is, they are both right. How can that be you ask? Good question.

The answer is relativity. What they see is relative to where they are. Mary sitting inside, is moving at the speed of the train but can’t see outside and doesn’t perceive the movement of the train so for her the only thing she sees moving is the ball that when hit moves at 10 miles an hour. For Bill, he has a different perspective as he sees the surroundings and sees the movement of the train with the movement of the ball. For Bill, the ball is moving much faster than it is for Mary.

That difference between what Mary sees and what Bill sees, is where you have to take your thought processes for the next few paragraphs as I explain Relativity as it comes to two and more different perspectives. These are good brain exercises because some of the theories on time travel are pretty far out there, almost like watching a script out of “The Twilight Zone.” Some seem like they must be complete fantasy but when you start to understand how our Universe works, you begin to understand the possibilities of some of the weirdest things you could only understand in some nightmarish dream. Whether it’s possible to pull any of these things off is another story because the technology even if possible is way beyond our capabilities with the still young technology we have today. Even though according the Einstein, we can never travel the exact speed of light, science says it should be possible to travel close to it, even 99% of it, just not “the speed of light.” The question is, is it really possible with all the pressures of traveling through space on a ship for us to ever make a ship that we can survive on traveling at the speeds we are talking about. Physics tells us that yes it is possible but is it really possible to make it happen? We won’t know until our technology catches up to our ideas. It still is fun to think about regardless but it’s even more important for us to try and find if it is possible. Maybe the goal, if there is other intelligent life in the Universe is, the first one to the edge of the Universe wins.

Time Travel

So if you have your mind open, let’s talk about time travel.

Using speed to time travel

As with the story with the train, we’re going to use Bill and Mary again. They are on break from school and trying to earn some money to pay off a few debts. Bill chooses to stay here on the Earth while Mary, ever the explorer, jumps at the chance to fly into space, into the galaxy and into the Universe.

Traveling at speeds close to the speed of light has a great effect for the travelers. You have probably heard or read that at these speeds, time slows down so much for the traveler that when the travelers return back to planet Earth, all their friends and everyone they knew are now dead as many years have passed on Earth since they first took off on their journey. This sounds like some wild science fiction movie but it is also true. For the travelers, with their ship traveling at speeds close to the speed of light, time had slowed for them according to the clocks of the people who kept track of the ship on Earth. The travelers, according to the people on the Earth, had been on their journey for a thousand years. For the travelers, the trip seemed like they were gone a couple years.

At this point, remember back to how the speed of the ping pong ball on the train was determined by what was relevant to the person looking at it. The same is true for time. Time always seems to be passing at the same rate for everyone everywhere. It’s when you compare time to two or more perspectives that you see that time from different perspectives is different. I know if you started not knowing what I am talking about, this last sentence didn’t help you much so I’ll explain it a different way which may be better. I mean this is pretty cool stuff to think about when you do get it.

Let’s go back to Bill and Mary. Bill and Mary synchronize their watches and then Mary takes off in her space ship and she travels at 99% the speed of light which is 669,600,000 miles an hour. Now for both Bill and Mary, time will seem to be passing at the same rate to each of them. Another way to put it is, let’s say that Mary and Bill are both 30 years old and we know that they are both going to pass away when they are 100 years old. If Bill spent the rest of his life on the Earth, the next 70 years would seem like 70 years to him, right? If Mary spent the rest of her life on her ship traveling close to the speed of light, the next 70 years would also to her seem like 70 years. Remember, time is relative to ones perspective. It’s when Bill and Mary meet again and they compare their watches that time dilation will show its face. In reality, thousands of years would pass between what Bill saw as 70 years and what Mary saw as 70 years.

If Mary was traveling close to the speed of light and she traveled for one year according to her watch before returning to Earth, she would return to find that close to 1300 years had passed on Earth. Also, Bill was no longer waiting for her. Relative to Mary, time had passed one year. It just took longer for that year to pass for Mary in her ship than it did for Bill on Earth. Even though 1300 years had passed on Earth, for Mary in her ship, she saw only one year had passed because she was traveling much faster than Bill on Earth and time slowed down for her and time passed at a slower rate than it did for Bill. Time seems like it’s passing at the same rate for everyone, everywhere but it’s not. Time itself is an illusion.

Now for the generations who after Bill was long gone, kept an eye on Mary’s space ship for the 1300 years she was gone, it would appear to them on Earth that Mary has been alive for 1300 years but that is not true because time is relative. To Mary, she feels like she’s a year older than when she left. Because Mary was traveling close to the speed of light, time was moving slower.

Remember that for those photons of light traveling the speed of light, time stands still. If you think that, if that is the case that time stands still, if you start to slow down from the speed of light, time will begin to move forward again. The tricky thing here is to know that as you keep slowing down, getting farther from the speed of light, time itself begins to move faster. The slower you get, the more time speeds up. It’s the same as with gravity. The closer you are to a gravity force the more time slows down and the further you get from a gravity source the more time speeds up. Someone living on the top of a mountain would age faster than someone living at the base of the mountaion, even though the time would be minusule. You don’t feel it because time is relative. Time feels the same to everyone everywhere, just as it is passing to you as you read this. Time feels like it’s passing at the same rate at every speed. We know that it is not. If Mary on her ship looks at her watch at 5 minute intervals, it will appear that 5 minutes has passed. If Bill on Earth looks at his watch at 5 minute intervals it will also appear to him that 5 minutes has passed. Time is relative to everyone everywhere and seems to pass at the same rate. In reality, those 5 minutes for Bill and Mary passed at vastly different speeds.

Just for the imagination now, what would happen if you went faster than the speed of light? If time moves slower the closer you get to the speed of light and stands still at the speed of light, theorists tell us that if you went faster than the speed of light, time would go in reverse and that makes sense. We don’t know of anything definitely that travels above the speed of light or that it’s even possible. We can only make educated guesses at this point. The possibilities are there that it could be true. It is also just as possible that those who say nothing can travel faster than light are right. That’s really a question hopefully future generations will be able answer.

 

[Norman Potting]

Did Dr Who explain it succinly in "Blink" - something to do with "wibbly, wobbly timey wimey stuff".

 

[Spiros]

If an astronaut was traveling close to the speed of light and he traveled for one year according to his watch before returning to Earth, he would return to find that close to 1300 years had passed on Earth.

Correct as that is per Stephen Hawking, you can't help but think that this is less time travel than time wasting. You can only travel in one direction.

 

[The Merry Prankster]

This is just a very, very dull period in the Earth's history and no-one can be arsed to visit us.

 

[Everest]

Copied and Pasted -

Time Dilation --- traveling close to the speed of light

This is where you have to expand your thinking somewhat. When it comes to the effects of traveling close to the speed of light, it sometimes appears to be mind-boggling when you hear some of the theories that talk about time travel and traveling the great, great distances to the stars in our galaxy and even more so to the other galaxies in the universe. The effects it has on the space travelers and to the people watching them on their home planet is something out of a science fiction novel. It is also true.

I’m going to try and make this as simple as possible because this can make you question what is and isn’t reality. I would guess with the speed of light, it’s a subject most have a hard time understanding because it is out there and it’s sometimes hard just to get your brain to go there, to be able to picture what these theories are implying. These are almost like brain exercises as you try to picture their concepts. It sometimes just leaves you saying, huh? Go back and read the paragraph again if you have to. Once you get it, you’ll find this isn’t all that hard to understand and the next thing will be a little easier until everything will start making sense. There’s one thing about the universe, it follows a strict set of rules, the “rules of nature” if you will. Something happens in our universe because something else happened to make that something happen. Got that? But it’s true. The universe is the way it is today because of all the different things that happened since the Big Bang roughly 14 billion years ago leading up to today. Everything happens because it had to happen.

I’ll begin with part of Einstein’s “Theory of Relativity.” One of the things this theory states is that “time” is relative to ones motion and also to the amount of gravity exerted on one. This is the theory everyone has heard. It says that the faster you travel, the more time slows for the traveler. This is true but only a part of the story. What does this mean? Let me give you an example. This is slightly different than the original but it represents a good example of two people seeing the same thing but with two different perspectives to what each is seeing. It was written by Steven Hawkings in his book “ A Briefer history of Time.” It is a great analogy of where your thinking has to go to understand what I’ll be talking about in a few paragraphs so I’ll use it again and thank the original writer.

It begins, there are two people. One (Bill), is standing on the platform of a railroad station waiting for the train to pull in. The other, Mary, is on a train coming towards the train station. The only thing abnormal about this scene is that the train on one side, the side facing the platform, is missing its side but only to anyone on the outside of the train. People on the outside of the train can see into one side of the train because that one side seems to be missing its wall, but if you’re inside the train it seems like the wall is there and you can’t see outside. I know it sounds weird but just follow me because we need it to be that way but it doesn’t have much to do with what we’ll be talking about. So again Bill on the platform can see into the train but Mary inside the train cannot see out. That’s easy enough. Now inside the train, Mary is sitting on a chair in the center of the train, against the wall on the side opposite of the train platform where Bill is standing and she is facing the platform side. As she sits, Mary is watching two people play ping pong on a table in the center of the train car. Looking at the train the player towards the back of the train is about to serve the ball towards his opponent on the side of the table towards the front of the train. He is serving in the direction the train is moving. At the same time he makes his first serve, the train is passing the train station platform. The train is moving at a speed of 90 miles an hour and traveling past the train station going to the next station.

Now as the train passes Bill on the platform, his eye catches the ping pong game so both he and Mary are watching the player make his first serve. Here comes the strange part of who, what, where and when. When the player hits the ball, the ball will be moving 10 miles an hour in the direction the train is moving. As Mary watches the player hit the ball, she sees the ball move towards his opponent at a speed of 10 miles an hour. Because Mary is traveling inside the train at the trains speed, she sees the ball hit and move at 10 miles an hour. As Bill watches standing on the platform, the train is wizzing by him at 90 miles an hour. When the ball is hit he sees the ball move at 100 miles an hour because he not only sees the ball move at 10 miles an hour, he also sees the train moving at 90 miles an hour so it appears to him that the ball is traveling 100 miles an hour. Which one is right, Mary who sees the ball move at 10 miles an hour or Bill who sees the ball move at 100 miles an hour. The answer is, they are both right. How can that be you ask? Good question.

The answer is relativity. What they see is relative to where they are. Mary sitting inside, is moving at the speed of the train but can’t see outside and doesn’t perceive the movement of the train so for her the only thing she sees moving is the ball that when hit moves at 10 miles an hour. For Bill, he has a different perspective as he sees the surroundings and sees the movement of the train with the movement of the ball. For Bill, the ball is moving much faster than it is for Mary.

That difference between what Mary sees and what Bill sees, is where you have to take your thought processes for the next few paragraphs as I explain Relativity as it comes to two and more different perspectives. These are good brain exercises because some of the theories on time travel are pretty far out there, almost like watching a script out of “The Twilight Zone.” Some seem like they must be complete fantasy but when you start to understand how our Universe works, you begin to understand the possibilities of some of the weirdest things you could only understand in some nightmarish dream. Whether it’s possible to pull any of these things off is another story because the technology even if possible is way beyond our capabilities with the still young technology we have today. Even though according the Einstein, we can never travel the exact speed of light, science says it should be possible to travel close to it, even 99% of it, just not “the speed of light.” The question is, is it really possible with all the pressures of traveling through space on a ship for us to ever make a ship that we can survive on traveling at the speeds we are talking about. Physics tells us that yes it is possible but is it really possible to make it happen? We won’t know until our technology catches up to our ideas. It still is fun to think about regardless but it’s even more important for us to try and find if it is possible. Maybe the goal, if there is other intelligent life in the Universe is, the first one to the edge of the Universe wins.

Time Travel

So if you have your mind open, let’s talk about time travel.

Using speed to time travel

As with the story with the train, we’re going to use Bill and Mary again. They are on break from school and trying to earn some money to pay off a few debts. Bill chooses to stay here on the Earth while Mary, ever the explorer, jumps at the chance to fly into space, into the galaxy and into the Universe.

Traveling at speeds close to the speed of light has a great effect for the travelers. You have probably heard or read that at these speeds, time slows down so much for the traveler that when the travelers return back to planet Earth, all their friends and everyone they knew are now dead as many years have passed on Earth since they first took off on their journey. This sounds like some wild science fiction movie but it is also true. For the travelers, with their ship traveling at speeds close to the speed of light, time had slowed for them according to the clocks of the people who kept track of the ship on Earth. The travelers, according to the people on the Earth, had been on their journey for a thousand years. For the travelers, the trip seemed like they were gone a couple years.

At this point, remember back to how the speed of the ping pong ball on the train was determined by what was relevant to the person looking at it. The same is true for time. Time always seems to be passing at the same rate for everyone everywhere. It’s when you compare time to two or more perspectives that you see that time from different perspectives is different. I know if you started not knowing what I am talking about, this last sentence didn’t help you much so I’ll explain it a different way which may be better. I mean this is pretty cool stuff to think about when you do get it.

Let’s go back to Bill and Mary. Bill and Mary synchronize their watches and then Mary takes off in her space ship and she travels at 99% the speed of light which is 669,600,000 miles an hour. Now for both Bill and Mary, time will seem to be passing at the same rate to each of them. Another way to put it is, let’s say that Mary and Bill are both 30 years old and we know that they are both going to pass away when they are 100 years old. If Bill spent the rest of his life on the Earth, the next 70 years would seem like 70 years to him, right? If Mary spent the rest of her life on her ship traveling close to the speed of light, the next 70 years would also to her seem like 70 years. Remember, time is relative to ones perspective. It’s when Bill and Mary meet again and they compare their watches that time dilation will show its face. In reality, thousands of years would pass between what Bill saw as 70 years and what Mary saw as 70 years.

If Mary was traveling close to the speed of light and she traveled for one year according to her watch before returning to Earth, she would return to find that close to 1300 years had passed on Earth. Also, Bill was no longer waiting for her. Relative to Mary, time had passed one year. It just took longer for that year to pass for Mary in her ship than it did for Bill on Earth. Even though 1300 years had passed on Earth, for Mary in her ship, she saw only one year had passed because she was traveling much faster than Bill on Earth and time slowed down for her and time passed at a slower rate than it did for Bill. Time seems like it’s passing at the same rate for everyone, everywhere but it’s not. Time itself is an illusion.

Now for the generations who after Bill was long gone, kept an eye on Mary’s space ship for the 1300 years she was gone, it would appear to them on Earth that Mary has been alive for 1300 years but that is not true because time is relative. To Mary, she feels like she’s a year older than when she left. Because Mary was traveling close to the speed of light, time was moving slower.

Remember that for those photons of light traveling the speed of light, time stands still. If you think that, if that is the case that time stands still, if you start to slow down from the speed of light, time will begin to move forward again. The tricky thing here is to know that as you keep slowing down, getting farther from the speed of light, time itself begins to move faster. The slower you get, the more time speeds up. It’s the same as with gravity. The closer you are to a gravity force the more time slows down and the further you get from a gravity source the more time speeds up. Someone living on the top of a mountain would age faster than someone living at the base of the mountaion, even though the time would be minusule. You don’t feel it because time is relative. Time feels the same to everyone everywhere, just as it is passing to you as you read this. Time feels like it’s passing at the same rate at every speed. We know that it is not. If Mary on her ship looks at her watch at 5 minute intervals, it will appear that 5 minutes has passed. If Bill on Earth looks at his watch at 5 minute intervals it will also appear to him that 5 minutes has passed. Time is relative to everyone everywhere and seems to pass at the same rate. In reality, those 5 minutes for Bill and Mary passed at vastly different speeds.

Just for the imagination now, what would happen if you went faster than the speed of light? If time moves slower the closer you get to the speed of light and stands still at the speed of light, theorists tell us that if you went faster than the speed of light, time would go in reverse and that makes sense. We don’t know of anything definitely that travels above the speed of light or that it’s even possible. We can only make educated guesses at this point. The possibilities are there that it could be true. It is also just as possible that those who say nothing can travel faster than light are right. That’s really a question hopefully future generations will be able answer.

Can't be bothered to read that all now.
I'll come back in the future and read it later - or earlier -or now

 

[Lady Whistledown]

Far MORE importantly: if you COULD travel in time...where (or when??) would you go?

 

[Everest]

Far MORE importantly: if you COULD travel in time...where (or when??) would you go?

I'd go back to 14.47 today and give Huple the answer before he'd asked the question.
That would stump his son

 

[Lady Whistledown]

I'd go back to 14.47 today and give Huple the answer before he'd asked the question.
That would stump his son

Good answer. On a purely footballing basis it'd probably have to be the 1983 cup final for me, as it was a couple of years before football registered on my radar and I'd love to see what it looked and felt like for a club like the Albion to reach the final in a time when it really, really mattered (as opposed to the commercial, Noddyfied over-hyped Big-Four-Fest it generally is now).

 

[H block]

I would go back to the seventies just to be able to take a picture of the pile of Dr Marten boots outside the north stand at the Goldstone before returning to the present time..

Because as Issiah the Yorkshireman says, ''You trying the youngsters about it today and they dont believe you''

 

[Acker79]

Copied and Pasted -

Time Dilation --- traveling close to the speed of light

This is where you have to expand your thinking somewhat. When it comes to the effects of traveling close to the speed of light, it sometimes appears to be mind-boggling when you hear some of the theories that talk about time travel and traveling the great, great distances to the stars in our galaxy and even more so to the other galaxies in the universe. The effects it has on the space travelers and to the people watching them on their home planet is something out of a science fiction novel. It is also true.

I’m going to try and make this as simple as possible because this can make you question what is and isn’t reality. I would guess with the speed of light, it’s a subject most have a hard time understanding because it is out there and it’s sometimes hard just to get your brain to go there, to be able to picture what these theories are implying. These are almost like brain exercises as you try to picture their concepts. It sometimes just leaves you saying, huh? Go back and read the paragraph again if you have to. Once you get it, you’ll find this isn’t all that hard to understand and the next thing will be a little easier until everything will start making sense. There’s one thing about the universe, it follows a strict set of rules, the “rules of nature” if you will. Something happens in our universe because something else happened to make that something happen. Got that? But it’s true. The universe is the way it is today because of all the different things that happened since the Big Bang roughly 14 billion years ago leading up to today. Everything happens because it had to happen.

I’ll begin with part of Einstein’s “Theory of Relativity.” One of the things this theory states is that “time” is relative to ones motion and also to the amount of gravity exerted on one. This is the theory everyone has heard. It says that the faster you travel, the more time slows for the traveler. This is true but only a part of the story. What does this mean? Let me give you an example. This is slightly different than the original but it represents a good example of two people seeing the same thing but with two different perspectives to what each is seeing. It was written by Steven Hawkings in his book “ A Briefer history of Time.” It is a great analogy of where your thinking has to go to understand what I’ll be talking about in a few paragraphs so I’ll use it again and thank the original writer.

It begins, there are two people. One (Bill), is standing on the platform of a railroad station waiting for the train to pull in. The other, Mary, is on a train coming towards the train station. The only thing abnormal about this scene is that the train on one side, the side facing the platform, is missing its side but only to anyone on the outside of the train. People on the outside of the train can see into one side of the train because that one side seems to be missing its wall, but if you’re inside the train it seems like the wall is there and you can’t see outside. I know it sounds weird but just follow me because we need it to be that way but it doesn’t have much to do with what we’ll be talking about. So again Bill on the platform can see into the train but Mary inside the train cannot see out. That’s easy enough. Now inside the train, Mary is sitting on a chair in the center of the train, against the wall on the side opposite of the train platform where Bill is standing and she is facing the platform side. As she sits, Mary is watching two people play ping pong on a table in the center of the train car. Looking at the train the player towards the back of the train is about to serve the ball towards his opponent on the side of the table towards the front of the train. He is serving in the direction the train is moving. At the same time he makes his first serve, the train is passing the train station platform. The train is moving at a speed of 90 miles an hour and traveling past the train station going to the next station.

Now as the train passes Bill on the platform, his eye catches the ping pong game so both he and Mary are watching the player make his first serve. Here comes the strange part of who, what, where and when. When the player hits the ball, the ball will be moving 10 miles an hour in the direction the train is moving. As Mary watches the player hit the ball, she sees the ball move towards his opponent at a speed of 10 miles an hour. Because Mary is traveling inside the train at the trains speed, she sees the ball hit and move at 10 miles an hour. As Bill watches standing on the platform, the train is wizzing by him at 90 miles an hour. When the ball is hit he sees the ball move at 100 miles an hour because he not only sees the ball move at 10 miles an hour, he also sees the train moving at 90 miles an hour so it appears to him that the ball is traveling 100 miles an hour. Which one is right, Mary who sees the ball move at 10 miles an hour or Bill who sees the ball move at 100 miles an hour. The answer is, they are both right. How can that be you ask? Good question.

The answer is relativity. What they see is relative to where they are. Mary sitting inside, is moving at the speed of the train but can’t see outside and doesn’t perceive the movement of the train so for her the only thing she sees moving is the ball that when hit moves at 10 miles an hour. For Bill, he has a different perspective as he sees the surroundings and sees the movement of the train with the movement of the ball. For Bill, the ball is moving much faster than it is for Mary.

That difference between what Mary sees and what Bill sees, is where you have to take your thought processes for the next few paragraphs as I explain Relativity as it comes to two and more different perspectives. These are good brain exercises because some of the theories on time travel are pretty far out there, almost like watching a script out of “The Twilight Zone.” Some seem like they must be complete fantasy but when you start to understand how our Universe works, you begin to understand the possibilities of some of the weirdest things you could only understand in some nightmarish dream. Whether it’s possible to pull any of these things off is another story because the technology even if possible is way beyond our capabilities with the still young technology we have today. Even though according the Einstein, we can never travel the exact speed of light, science says it should be possible to travel close to it, even 99% of it, just not “the speed of light.” The question is, is it really possible with all the pressures of traveling through space on a ship for us to ever make a ship that we can survive on traveling at the speeds we are talking about. Physics tells us that yes it is possible but is it really possible to make it happen? We won’t know until our technology catches up to our ideas. It still is fun to think about regardless but it’s even more important for us to try and find if it is possible. Maybe the goal, if there is other intelligent life in the Universe is, the first one to the edge of the Universe wins.

Time Travel

So if you have your mind open, let’s talk about time travel.

Using speed to time travel

As with the story with the train, we’re going to use Bill and Mary again. They are on break from school and trying to earn some money to pay off a few debts. Bill chooses to stay here on the Earth while Mary, ever the explorer, jumps at the chance to fly into space, into the galaxy and into the Universe.

Traveling at speeds close to the speed of light has a great effect for the travelers. You have probably heard or read that at these speeds, time slows down so much for the traveler that when the travelers return back to planet Earth, all their friends and everyone they knew are now dead as many years have passed on Earth since they first took off on their journey. This sounds like some wild science fiction movie but it is also true. For the travelers, with their ship traveling at speeds close to the speed of light, time had slowed for them according to the clocks of the people who kept track of the ship on Earth. The travelers, according to the people on the Earth, had been on their journey for a thousand years. For the travelers, the trip seemed like they were gone a couple years.

At this point, remember back to how the speed of the ping pong ball on the train was determined by what was relevant to the person looking at it. The same is true for time. Time always seems to be passing at the same rate for everyone everywhere. It’s when you compare time to two or more perspectives that you see that time from different perspectives is different. I know if you started not knowing what I am talking about, this last sentence didn’t help you much so I’ll explain it a different way which may be better. I mean this is pretty cool stuff to think about when you do get it.

Let’s go back to Bill and Mary. Bill and Mary synchronize their watches and then Mary takes off in her space ship and she travels at 99% the speed of light which is 669,600,000 miles an hour. Now for both Bill and Mary, time will seem to be passing at the same rate to each of them. Another way to put it is, let’s say that Mary and Bill are both 30 years old and we know that they are both going to pass away when they are 100 years old. If Bill spent the rest of his life on the Earth, the next 70 years would seem like 70 years to him, right? If Mary spent the rest of her life on her ship traveling close to the speed of light, the next 70 years would also to her seem like 70 years. Remember, time is relative to ones perspective. It’s when Bill and Mary meet again and they compare their watches that time dilation will show its face. In reality, thousands of years would pass between what Bill saw as 70 years and what Mary saw as 70 years.

If Mary was traveling close to the speed of light and she traveled for one year according to her watch before returning to Earth, she would return to find that close to 1300 years had passed on Earth. Also, Bill was no longer waiting for her. Relative to Mary, time had passed one year. It just took longer for that year to pass for Mary in her ship than it did for Bill on Earth. Even though 1300 years had passed on Earth, for Mary in her ship, she saw only one year had passed because she was traveling much faster than Bill on Earth and time slowed down for her and time passed at a slower rate than it did for Bill. Time seems like it’s passing at the same rate for everyone, everywhere but it’s not. Time itself is an illusion.

Now for the generations who after Bill was long gone, kept an eye on Mary’s space ship for the 1300 years she was gone, it would appear to them on Earth that Mary has been alive for 1300 years but that is not true because time is relative. To Mary, she feels like she’s a year older than when she left. Because Mary was traveling close to the speed of light, time was moving slower.

Remember that for those photons of light traveling the speed of light, time stands still. If you think that, if that is the case that time stands still, if you start to slow down from the speed of light, time will begin to move forward again. The tricky thing here is to know that as you keep slowing down, getting farther from the speed of light, time itself begins to move faster. The slower you get, the more time speeds up. It’s the same as with gravity. The closer you are to a gravity force the more time slows down and the further you get from a gravity source the more time speeds up. Someone living on the top of a mountain would age faster than someone living at the base of the mountaion, even though the time would be minusule. You don’t feel it because time is relative. Time feels the same to everyone everywhere, just as it is passing to you as you read this. Time feels like it’s passing at the same rate at every speed. We know that it is not. If Mary on her ship looks at her watch at 5 minute intervals, it will appear that 5 minutes has passed. If Bill on Earth looks at his watch at 5 minute intervals it will also appear to him that 5 minutes has passed. Time is relative to everyone everywhere and seems to pass at the same rate. In reality, those 5 minutes for Bill and Mary passed at vastly different speeds.

Just for the imagination now, what would happen if you went faster than the speed of light? If time moves slower the closer you get to the speed of light and stands still at the speed of light, theorists tell us that if you went faster than the speed of light, time would go in reverse and that makes sense. We don’t know of anything definitely that travels above the speed of light or that it’s even possible. We can only make educated guesses at this point. The possibilities are there that it could be true. It is also just as possible that those who say nothing can travel faster than light are right. That’s really a question hopefully future generations will be able answer.

So, to put it simply, Einstein's theory of relativity?

I find KG's explanation easier to understand (speed travelled plus time passing always = x, if one increases the other decreases to maintain the constant of x), but I'm not sure if it's the same thing or not.

It begins, there are two people. One (Bill), is standing on the platform of a railroad station waiting for the train to pull in. The other, Mary, is on a train coming towards the train station. The only thing abnormal about this scene is that the train on one side, the side facing the platform, is missing its side but only to anyone on the outside of the train. People on the outside of the train can see into one side of the train because that one side seems to be missing its wall, but if you’re inside the train it seems like the wall is there and you can’t see outside. I know it sounds weird but just follow me because we need it to be that way but it doesn’t have much to do with what we’ll be talking about. So again Bill on the platform can see into the train but Mary inside the train cannot see out. That’s easy enough. Now inside the train, Mary is sitting on a chair in the center of the train, against the wall on the side opposite of the train platform where Bill is standing and she is facing the platform side. As she sits, Mary is watching two people play ping pong on a table in the center of the train car. Looking at the train the player towards the back of the train is about to serve the ball towards his opponent on the side of the table towards the front of the train. He is serving in the direction the train is moving. At the same time he makes his first serve, the train is passing the train station platform. The train is moving at a speed of 90 miles an hour and traveling past the train station going to the next station.

Now as the train passes Bill on the platform, his eye catches the ping pong game so both he and Mary are watching the player make his first serve. Here comes the strange part of who, what, where and when. When the player hits the ball, the ball will be moving 10 miles an hour in the direction the train is moving. As Mary watches the player hit the ball, she sees the ball move towards his opponent at a speed of 10 miles an hour. Because Mary is traveling inside the train at the trains speed, she sees the ball hit and move at 10 miles an hour. As Bill watches standing on the platform, the train is wizzing by him at 90 miles an hour. When the ball is hit he sees the ball move at 100 miles an hour because he not only sees the ball move at 10 miles an hour, he also sees the train moving at 90 miles an hour so it appears to him that the ball is traveling 100 miles an hour. Which one is right, Mary who sees the ball move at 10 miles an hour or Bill who sees the ball move at 100 miles an hour.

I want to see this put into practice. (Not because I doubt the theory, I just think it seems like an impressive experiment)

 

[Shifty89]

This is just a very, very dull period in the Earth's history and no-one can be arsed to visit us.

Dull period in Earth's history?! are you mad?! Albion are top of the league and soon to move into our spectacular new home! Dull indeed...

 

[Questions]

Time travel ?


Not again. We did this one next wednesday.

 

[blue'n'white]

Well if time travel IS possible can someone give me this Friday's Euromillions numbers please !!
Ta lots

 

[the hitman]

Time travel is impossible