Time travel explained.....
Ok, let's talk time travel...1st of all we are all time travellers in that we are all travelling forward through time...but I know that's not what you mean.
Contrary to popular belief, time travel IS possible but it's only possible to travel into the future. Whether time travel to the past is possible (even in principle) is still an open question...we'll get to that in a moment...1st time travel into the future...Einstein showed in his special theory of relativity that as one accelerates closer and closer to the speed of light, time dilates or slows down. The effects are very small at lower speeds but have been proven correct by comparing atomic powered clocks flown on jets.
Consider this example. Suppose we travel in a spaceship to the nearest star just over 4 light years away at say 99.99% the speed of light (beyond todays technology but pretend). The round trip as seen from observers on earth would be a little over 8 years, but to occupants on the ship, they would feel like they traveled for only a little over 8 weeks! In essence. the crew would have travelled into our future by 4 years! I Go faster for longer (say 99.99999% lightspeed) you could come back literally millions of years into the future!
Later Einstein also discovered that high gravity can affect time the same way.
Again the effects are small for earth type gravity but if we say take our imaginary spaceship very near a black hole that has an immense gravitational field. As long as we were careful not to cross the black hole's 'event horizon' (the point of no escape) we could travel far into the future.
Now what about backwards? Many believe that for the same reason you cite, that backward time travel is impossible because it causes paradoxes. These paradoxes take different forms but all come down to the same thing...we change something that means we could not have changed it.
Here are some of the common paradoxes normally cited.
The Grandfather Paradox:
I go back in time and kill my own grandfather so I cannot be born, and therefore cannot go back in time to kill my grandfather.
The Chicken or the Egg Paradox:
I'm a scientist struggling to invent a time machine...my future self was successful and travels back in time to tell me the secret. I use the secret and invent the time machine...I'm now my future self and I travel back in time to give my past self the secret...The problem is this is an infinite loop...I couldn't invent the time machine until I knew the secret from my future self but my future self couldn't tell me the secret until I was successful!
The Many Me's Paradox.
I invent a time machine. I immediately travel 1 second back in time and meet myself. Then the 2 of us travel back 1 second and meat the two of us, then 4, 8, 16...
30 iterations and there would be over a billion of us, 10 more iterations and there's over a trillion of us... I / We could easily take over and enslave the world!
The TOURISM Paradox:
If you invented a time machine, who would you like to meet? What historical event would you like to witness 1st hand? The fact that we don't see a trillion trillion "tourists" popping up when Christ is crucified, or Kennedy is shot proves time travel is impossible.
It's for these reasons many see backward time travel as impossible.
HOWEVER, that said, there are those that try to get around thes limitations. The common ways are as follows.
The MANY WORLDS Theory:
This theory says that instead of one single "time" path there are many parallel paths. When I travel back in time I go to a parallel, abeit identicle, universe. I can kill my grandfather and so in THAT universe I won't be born but in THIS universe, the one I left, my grandfather was never killed and I could still exist to travel back in time.
The SELF CONSISTENCY Theory:
This theory says there is only one universe but it has some kind of 'built in' "history conservation law" that says if I go back in time, anything I do was suppose to happen! And anything I try to do to "disrupt" the future (or history depending on your point of view!) will be prevented.
I go back in time to kill my grandfather but no matter what I do I'm always foiled. The gun fails, or I can't get a cab to his house or the bullet misses him but breaks a window and then I remember him telling me a story about one day when someone mysterious tried to kill him but he survived etc.
A final way out of paradoxes is to say yes backward time travel is possible but only back to the point the time machine was 1st invented! So say the time machine gets invented in 2020. It's only THEN that we'll start to see time travellers from the future popping up. So now my future self can't go back in time to tell my past self the secret to time travel until my past self actually invents the machine!
And so it goes on...point counterpoint until your are dizzy thinking about it..take a couple tylenols and lay down now until you are feeling better.
2 years ago
Ok, let's talk time travel...1st of all we are all time travellers in that we are all travelling forward through time...but I know that's not what you mean.
Contrary to popular belief, time travel IS possible but it's only possible to travel into the future. Whether time travel to the past is possible (even in principle) is still an open question...we'll get to that in a moment...1st time travel into the future...Einstein showed in his special theory of relativity that as one accelerates closer and closer to the speed of light, time dilates or slows down. The effects are very small at lower speeds but have been proven correct by comparing atomic powered clocks flown on jets.
Consider this example. Suppose we travel in a spaceship to the nearest star just over 4 light years away at say 99.99% the speed of light (beyond todays technology but pretend). The round trip as seen from observers on earth would be a little over 8 years, but to occupants on the ship, they would feel like they traveled for only a little over 8 weeks! In essence. the crew would have travelled into our future by 4 years! I Go faster for longer (say 99.99999% lightspeed) you could come back literally millions of years into the future!
Later Einstein also discovered that high gravity can affect time the same way.
Again the effects are small for earth type gravity but if we say take our imaginary spaceship very near a black hole that has an immense gravitational field. As long as we were careful not to cross the black hole's 'event horizon' (the point of no escape) we could travel far into the future.
Now what about backwards? Many believe that for the same reason you cite, that backward time travel is impossible because it causes paradoxes. These paradoxes take different forms but all come down to the same thing...we change something that means we could not have changed it.
Here are some of the common paradoxes normally cited.
The Grandfather Paradox:
I go back in time and kill my own grandfather so I cannot be born, and therefore cannot go back in time to kill my grandfather.
The Chicken or the Egg Paradox:
I'm a scientist struggling to invent a time machine...my future self was successful and travels back in time to tell me the secret. I use the secret and invent the time machine...I'm now my future self and I travel back in time to give my past self the secret...The problem is this is an infinite loop...I couldn't invent the time machine until I knew the secret from my future self but my future self couldn't tell me the secret until I was successful!
The Many Me's Paradox.
I invent a time machine. I immediately travel 1 second back in time and meet myself. Then the 2 of us travel back 1 second and meat the two of us, then 4, 8, 16...
30 iterations and there would be over a billion of us, 10 more iterations and there's over a trillion of us... I / We could easily take over and enslave the world!
The TOURISM Paradox:
If you invented a time machine, who would you like to meet? What historical event would you like to witness 1st hand? The fact that we don't see a trillion trillion "tourists" popping up when Christ is crucified, or Kennedy is shot proves time travel is impossible.
It's for these reasons many see backward time travel as impossible.
HOWEVER, that said, there are those that try to get around thes limitations. The common ways are as follows.
The MANY WORLDS Theory:
This theory says that instead of one single "time" path there are many parallel paths. When I travel back in time I go to a parallel, abeit identicle, universe. I can kill my grandfather and so in THAT universe I won't be born but in THIS universe, the one I left, my grandfather was never killed and I could still exist to travel back in time.
The SELF CONSISTENCY Theory:
This theory says there is only one universe but it has some kind of 'built in' "history conservation law" that says if I go back in time, anything I do was suppose to happen! And anything I try to do to "disrupt" the future (or history depending on your point of view!) will be prevented.
I go back in time to kill my grandfather but no matter what I do I'm always foiled. The gun fails, or I can't get a cab to his house or the bullet misses him but breaks a window and then I remember him telling me a story about one day when someone mysterious tried to kill him but he survived etc.
A final way out of paradoxes is to say yes backward time travel is possible but only back to the point the time machine was 1st invented! So say the time machine gets invented in 2020. It's only THEN that we'll start to see time travellers from the future popping up. So now my future self can't go back in time to tell my past self the secret to time travel until my past self actually invents the machine!
And so it goes on...point counterpoint until your are dizzy thinking about it..take a couple tylenols and lay down now until you are feeling better.
2 years ago
