Intergalactic space travel is possible

[Endercreeper01]

Intergalactic space travel is possible and will not take a huge amount of time to get there because of special relativity. If we go at speeds very close to the speed of light, then the time it takes relative to us and the length of the trip relative to us would be shorter because of special relativity. Time is relative, and in special relativity, then if an observer sees something with a relative velocity v, then the time that passes for that object relative to the observer t'=t(1-v²/c²)^1/2. Same with length. The length would be l'=l(1-v²/c²)^1/2. But this is relative. Relative to us, then we are staying still, and everything else is moving, so then everything else contracts by that amount, making t a shorter trip. And same with time dilation. Relative to us, it seems everything else slows down. And because of this, then intergalactic space travel is possible and will not take so much time. Is this correct?

[imatfaal]

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Moderator Note

will you stop posting everything twice please.

[Endercreeper01]

!

Moderator Note

will you stop posting everything twice please.

sorry that is a glitch that happens on my computer

[mathematic]

Intergalactic space travel is possible and will not take a huge amount of time to get there because of special relativity. If we go at speeds very close to the speed of light, then the time it takes relative to us and the length of the trip relative to us would be shorter because of special relativity. Time is relative, and in special relativity, then if an observer sees something with a relative velocity v, then the time that passes for that object relative to the observer t'=t(1-v²/c²)^1/2. Same with length. The length would be l'=l(1-v²/c²)^1/2. But this is relative. Relative to us, then we are staying still, and everything else is moving, so then everything else contracts by that amount, making t a shorter trip. And same with time dilation. Relative to us, it seems everything else slows down. And because of this, then intergalactic space travel is possible and will not take so much time. Is this correct?

In theory you are correct. However, there are practical problems. You need to do a lot of accelerating to get up to close to the speed of light. Once you reach top speed, you will be going very fast relative to most things, collision avoidance becomes a very serious issue. I am sure there are many other difficuties as well.

[Endercreeper01]

In theory you are correct. However, there are practical problems. You need to do a lot of accelerating to get up to close to the speed of light. Once you reach top speed, you will be going very fast relative to most things, collision avoidance becomes a very serious issue. I am sure there are many other difficuties as well.

Yes, but it still works if we find a way around those things

[Enthalpy]

Travel would be faster for the travellers, as is known, but not for people staying on Earth and waiting for reports about the remote galaxy.

 

Yes, but it still works if we find a way around those things

 

And here I just react as an engineer and ask: "How"?

 

Because, well, current technology achieves a few times 5km/s. I very proudly proposed one propulsion that will achieve few times 10km/s. Some processes (fission fragments' kinetic energy) for which no-one can suggest an implementation would conceivably achieve 3000km/s. That's still a factor-of-100 to approach c.

[Janus]

Yes, but it still works if we find a way around those things

Here's the thing, you are talking about intergalactic travel. In order to get to even the nearest galaxy in a single lifetime and stop upon arrival, using the the most efficient rocket drive theorectically possible (photon rocket with antimatter fuel), you would need something like 4.2 million million kg of fuel for every kg of payload delivered.

 

This is not something that can be engineered around.

[Endercreeper01]

Here's the thing, you are talking about intergalactic travel. In order to get to even the nearest galaxy in a single lifetime and stop upon arrival, using the the most efficient rocket drive theorectically possible (photon rocket with antimatter fuel), you would need something like 4.2 million million kg of fuel for every kg of payload delivered.

 

This is not something that can be engineered around.

we can stop whenever we get to another planet to get more fuel

 

And here I just react as an engineer and ask: "How"?

 

Because, well, current technology achieves a few times 5km/s. I very proudly proposed one propulsion that will achieve few times 10km/s.

Tell me all about it.

Travel would be faster for the travellers, as is known, but not for people staying on Earth and waiting for reports about the remote galaxy.

 

Relative to earthlings, time slows down for the spaceship and so it takes longer for them to age and they both agree on a certian time it takes them

And even if we can't do intergactic space travel, we can do interstellar

[Janus]

we can stop whenever we get to another planet to get more fuel

 

That's kind of pointless unless the planet is your actual destination.

 

Let's say I want to get to a planet 1000 ly away, but I need to make the trip in 10 yrs by my time. To do so, I have to get up to ~0.99995c. It will take a given amount of fuel to get up to that speed and a given amount of fuel to slow back down, no matter how far I travel. In other words, if I accelerate up to that speed travel for 1000 ly and slow down at the end, I would use the same fuel as if I accelerated up to the same speed, traveled for 10 ly and then slowed back down. I gain nothing by breaking the trip into smaller legs and refueling after each leg. If anything, I'm making the trip longer because of the extra time needed for the acceleration and deceleration phases of the trip.

[xyzt]

Here's the thing, you are talking about intergalactic travel. In order to get to even the nearest galaxy in a single lifetime and stop upon arrival, using the the most efficient rocket drive theorectically possible (photon rocket with antimatter fuel), you would need something like 4.2 million million kg of fuel for every kg of payload delivered.

 

This is not something that can be engineered around.

Yep, there is a professor that puts forward the fuel problem to his students EVERY year and, like clockwork, the answer comes back: "Nope. Not possible". It is an issue of fuel, indeed.

 

That's kind of pointless unless the planet is your actual destination.

 

Let's say I want to get to a planet 1000 ly away, but I need to make the trip in 10 yrs by my time. To do so, I have to get up to ~0.99995c. It will take a given amount of fuel to get up to that speed and a given amount of fuel to slow back down, no matter how far I travel. In other words, if I accelerate up to that speed travel for 1000 ly and slow down at the end, I would use the same fuel as if I accelerated up to the same speed, traveled for 10 ly and then slowed back down. I gain nothing by breaking the trip into smaller legs and refueling after each leg. If anything, I'm making the trip longer because of the extra time needed for the acceleration and deceleration phases of the trip.

Actually, starting and stopping to take fuel is a lot worse. Absent any resistance, once you achieve cruising speed you let inertia take over, the ship should maintain speed w/o using any more fuel. The problem is that ramping up to 0.999...c takes too much fuel by itself.

Edited August 15, 2013 by xyzt

[Didymus]

 

Still say if you believe that only 10 years actually passes during that 1000LY trip, then you're insinuating that traveling at .99995c=100c.

 

If you travel 100 lightyears per year....

 

Only way around that is to admit that time and space don't change, only the traveler's perception of time and space.... Meaning that even if it slowed all biological and atomic function by a factor of 100.... They've still been traveling for 1000 years.

Edited August 15, 2013 by Didymus

[Endercreeper01]

Ok, mabey we can't do intergalactic soace travel, but we can do interstellar

[Janus]

Still say if you believe that only 10 years actually passes during that 1000LY trip, then you're insinuating that traveling at .99995c=100c.

 

If you travel 100 lightyears per year....

 

Only way around that is to admit that time and space don't change, only the traveler's perception of time and space.... Meaning that even if it slowed all biological and atomic function by a factor of 100.... They've still been traveling for 1000 years.

 

No, because according to the traveler, the distance traveled at 0.99995c is only ~10 light years. The distance between the Earth and distant planet has undergone length contraction due to it's high relative speed to the space ship.

 

It is not just a matter of "perspective". In the space ship frame, the distance really is ~10 light years and his measurement of this distance is no less the "real" distance as the 1000 light years measured by someone on Earth.