that means it takes light 20 years to reach the star
if a ship went the speed of light it would take the same 20 years
if a ship went half the speed of light it would take half the time
simple
I'm "over complicating this" because it's complicated. If you study Einstein's theory of Special Relativity you'd understand why. Now I'm not going to go into the details of the theory as it is known to give people headaches, but the theory predicts two strange phenomena (which have been empirically verified) known as time dilation and length contradiction.
To give a very crude explanation, the first phenomena can be stated that moving clocks run slower, and the second phenomena can be stated that moving objects contract in length (become shorter). The amount of time dilation or length contraction depends on the speed of the moving object. ie: the faster the object is moving, the slower the clock runs, and the shorter the object becomes.
So if a space craft is traveling at great speeds (near the speed of light), then to an observer on earth, it would appear as if the space ship's clock runs slower. Hence the time elapsed on the space ship is shorter than the time elapsed on earth.
Now imagine there is a stick placed in between the earth and the star, which represents their distance. To a person on earth, the stick would be stationary, but from the perspective of the space ship the stick would be moving (same way as if your riding in a car, you could perceive this as the ground moving). As I said, the length of moving objects contract, so the length of this stick would be shorter to someone in the space ship than it would be to someone on earth. ie: the distance between the star and the earth is shorter for people in the space ship than to someone on earth.
You may be wondering "why don't I notice the effects of time dilation and length contraction? When I throw a brick, I don't see it's length become shorter." The reason why we don't notice this in every day life is because the effects are more apparent the closer the moving object approaches the speed of light. This is why it would take a space ship 34.6 years traveling at .5c, but would only take 2.8 years traveling at .99c. A thrown brick travels nowhere near the speed of light, but its length does contract, its just on such a small order of magnitude that it isn't observable.
Like I said this is a very very crude explanation, and there are dozens of books which can explain this in much greater depth and detail. If your interested I recommend you check out "Spacetime Physics" by Taylor & Wheeler, or "Special Relativity" by A P French.
thank you for that explaination...it is fasinating
question though...is this all just "theory"...as it relates to Einsteins "theory of relativity"? or is this an actual law of science?
np.
It's a theory in the sense of the scientific definition of theory (which is much stronger than in common language). It's been around for a hundred years and has been verified by numerous experiments. Physicists at this point would treat it as fact. However, just like any scientific theory, it is still open to possible modifications or could even be thrown out all together, but there would need to be some kind of experimental to warrant such actions.
I'm "over complicating this" because it's complicated. If you study Einstein's theory of Special Relativity you'd understand why. Now I'm not going to go into the details of the theory as it is known to give people headaches, but the theory predicts two strange phenomena (which have been empirically verified) known as time dilation and length contradiction.
To give a very crude explanation, the first phenomena can be stated that moving clocks run slower, and the second phenomena can be stated that moving objects contract in length (become shorter). The amount of time dilation or length contraction depends on the speed of the moving object. ie: the faster the object is moving, the slower the clock runs, and the shorter the object becomes.
So if a space craft is traveling at great speeds (near the speed of light), then to an observer on earth, it would appear as if the space ship's clock runs slower. Hence the time elapsed on the space ship is shorter than the time elapsed on earth.
Now imagine there is a stick placed in between the earth and the star, which represents their distance. To a person on earth, the stick would be stationary, but from the perspective of the space ship the stick would be moving (same way as if your riding in a car, you could perceive this as the ground moving). As I said, the length of moving objects contract, so the length of this stick would be shorter to someone in the space ship than it would be to someone on earth. ie: the distance between the star and the earth is shorter for people in the space ship than to someone on earth.
You may be wondering "why don't I notice the effects of time dilation and length contraction? When I throw a brick, I don't see it's length become shorter." The reason why we don't notice this in every day life is because the effects are more apparent the closer the moving object approaches the speed of light. This is why it would take a space ship 34.6 years traveling at .5c, but would only take 2.8 years traveling at .99c. A thrown brick travels nowhere near the speed of light, but its length does contract, its just on such a small order of magnitude that it isn't observable.
Like I said this is a very very crude explanation, and there are dozens of books which can explain this in much greater depth and detail. If your interested I recommend you check out "Spacetime Physics" by Taylor & Wheeler, or "Special Relativity" by A P French.
We learnt all this in Physics 11 (as in grade 11) is no one else familiar with it? Didn't you learn this in high school? But you sir explain it quite nicely!
A star being 20 light years away does not mean if you traveled (in a space craft) at the speed of light that it would take you 20 years to get there, nor would it take you 40 years traveling half the speed of light.
As was already mentioned it's impossible to travel at the speed of light. But lets, for examples sake, say you were traveling in a space ship to a star 20 light years away at 99% the speed of light or 0.99c. Then it would only take you approximately 2.8 years to get there. However to an observer on earth, the trip would take about 20 years.
Similarly if you were traveling at half the speed of light or 0.5c then it would take you approximately 36.4 years to complete the trip, but to an observer on earth, it would take 40 years.
Seem strange? Welcome to the marvels of Special Relativity known as length contraction and time dilation.
so if you travel at the speed of light for 2.8 years.(20 on earth) and you travel back at the same speed for 2.8 years now forty on earth would that be considered a form of time travel? for you would only be gone 5 years but the world will have aged 40
also imagine that while you were gone virtually everyone in the space agency that was on staff when you left would be dead or retired..
or this while your gone, 20 years passes on earth and technology evolves and the space administration builds a faster craft that takes off 5 years after you but actually arrives at the destination before you do
they probably were people on that planet but they polluted so much they killed themselves.you can tell that they are older cause the sun is less strong.
so if you travel at the speed of light for 2.8 years.(20 on earth) and you travel back at the same speed for 2.8 years now forty on earth would that be considered a form of time travel? for you would only be gone 5 years but the world will have aged 40
also imagine that while you were gone virtually everyone in the space agency that was on staff when you left would be dead or retired..
Yeah, that would be a way to travel forward in time since, like you said, upon the travelers return he would have only aged about 5 years while the earth had aged 40. If this were too really happen, I'm sure an agency like NASA would have no problem integrating new staff on the project. NASA is currently working on projects that will last for several decades.
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or this while your gone, 20 years passes on earth and technology evolves and the space administration builds a faster craft that takes off 5 years after you but actually arrives at the destination before you do
Hmm, I'm not sure what your suggesting, but given the above example, I'd say this was either impossible or not yet solvable. If 20 years passes by on earth, than the first ship (call it A) would have already reached its destination, so to send a new ship (call it B) five years later and have it reach the destination before ship A would require that ship B travel backwards in time. To my knowledge going backwards in time is debatable.
Lol, the string theory is a joke. It has been discredited and mangled, but only recently. Going backward in time is most likely impossible...but who knows, but I wouldn't rely on the string theory to prove anything.
Lol, the string theory is a joke. It has been discredited and mangled, but only recently. Going backward in time is most likely impossible...but who knows, but I wouldn't rely on the string theory to prove anything.
you are right, it is just a "theory" and isn't proof of anything what so ever but at the same time I wouldn't call it a joke...
and I also wouldn't call anything impossible at this point...if time is on a plane then there must be some off the wall way that could make going back in time possible....
Re: another planet like earth found
