Relativity and time question for physics enthusiasts

[Eli]

Originally posted by: Heisenberg

Originally posted by: silverpig
Light takes 8 years round trip. You travel at 99.9% light speed, you do the trip in 1/0.999 of 8 = 1.001001001 years from earth's perspective. To you in the ship this would be 8/14.1 = 0.567 years.

So you basically travel 8 ly in 0.567 years

This doesn't violate relativity though

I agree, but you have to be careful about how you word things. To YOU on the ship, the trip would still take 8 years. It's not like you'd see your watch suddenly run slow as you sped up. To everyone on earth, it would also take 8 years, but you'd have only aged 0.567 years to them when you returned.

Also, you have to keep in mind that the person on the ship is in two different intertial frames: one on the way, and a different one on the way back. Since special relativity deals with inertial frames moving w/respect to each other at uniform speed, you really have to look at the time dilation from the Earth's viewpoint.

*head explodes*

So you would be concious for 8 years, remember everything from the 8 years.. It would be 8 years to you, and to everybody on Earth..

But the cells in your body will have only truely experienced 0.567 years?

Am I understanding that right? LOL....

 

[Heisenberg]

Originally posted by: RaynorWolfcastle
I haven't done any relativity stuff in a while but somehow that doesn't sound right... If you experience that it takes 8 years to make the trip you age 8 years, right?

I'm under the impression that the traveller would only feel the trip to be 0.567 years long because of length contraction, no? Admittedly, I could be completely in left field about this

No, length contraction and time dilation are two different effects (although they both come from Lorentz transformations). The apparent paradox you bring up is why you have to be careful about what you consider an inertial reference frame. Since the traveler in is two different frames, you can only correctly apply the time dilation equation from the Earth's viewpoint.

 

[Heisenberg]

Originally posted by: Eli
*head explodes*

So you would be concious for 8 years, remember everything from the 8 years.. It would be 8 years to you, and to everybody on Earth..

But the cells in your body will have only truely experienced 0.567 years?

Am I understanding that right? LOL....

It depends on what you mean by "truely". With relativity, there is no absolute reference frame. To the people on earth yes, you would have only aged 0.567 years.

Edit: Forgot about length contraction.

 

[TuxDave]

This is how I see it. To the people on earth, they see my trip taking 8 years. They see me aging 8/14.1 years due to time dilation.

As the person on the ship, I experience length contraction such that the roundtrip is 8/14.1 light years away which is why I would think that I only had to travel 0.567 years if moving at 99.99% the speed of light.

So upon returning to the earth, I and the people on earth see me aged 8/14.1 years while they aged 8 years.

 

[RaynorWolfcastle]

Right, but the length contraction would then be perceived from the traveler's frame, making the star "appear closer" and shortening the trip from his time frame, no?

I think it's about time I break out the old physics books

TuxDave, that's the way I see it too; but I haven't looked at this in awhile so I'm not certain it is the correct way to interpret it.

 

[hjo3]

Originally posted by: Eli
So you would be concious for 8 years, remember everything from the 8 years.. It would be 8 years to you, and to everybody on Earth..

But the cells in your body will have only truely experienced 0.567 years?

Am I understanding that right? LOL....

Nope; to you it will seem like you climbed into the spaceship and sat around for 0.567 years. When you land and get off the ship, everyone else will be like "Whoa, you were gone for 8 years!" And you'll be like "What? I was only gone for like 6 months!" You will have been slowed for those 8 years, physically and mentally. When you watched a 30-minute episode of Ren & Stimpy on the spaceship it only seemed like 30 minutes. But relative to the ppl on Earth, it took you 7 HOURS to watch that show.

 

[Eli]

Originally posted by: hjo3

Originally posted by: Eli
So you would be concious for 8 years, remember everything from the 8 years.. It would be 8 years to you, and to everybody on Earth..

But the cells in your body will have only truely experienced 0.567 years?

Am I understanding that right? LOL....

Nope; to you it will seem like you climbed into the spaceship and sat around for 0.567 years. When you land and get off the ship, everyone else will be like "Whoa, you were gone for 8 years!" And you'll be like "What? I was only gone for like 6 months!" You will have been slowed for those 8 years, physically and mentally. When you watched a 30-minute episode of Ren & Stimpy on the spaceship it only seemed like 30 minutes. But relative to the ppl on Earth, it took you 7 HOURS to watch that show.

Ahh.. Yeah. That's what I thought.

Wow.. What a bizzare concept.. So did Einstein just whip that out of his ass one day or what? lol

 

[Heisenberg]

Originally posted by: RaynorWolfcastle
Right, but the length contraction would then be perceived from the traveler's frame, making the star "appear closer" and shortening the trip from his time frame, no?

I think it's about time I break out the old physics books

TuxDave, that's the way I see it too; but I haven't looked at this in awhile so I'm not certain it is the correct way to interpret it.

Crap. Yeah, you're right. You have to take into account the length contraction.

 

[TuxDave]

Originally posted by: RaynorWolfcastle
Right, but the length contraction would then be perceived from the traveler's frame, making the star "appear closer" and shortening the trip from his time frame, no?

I think it's about time I break out the old physics books

TuxDave, that's the way I see it too; but I haven't looked at this in awhile so I'm not certain it is the correct way to interpret it.

haha... yeah, I dunno if that's the most accurate way to describe it. It's the only way relativity makes any sense to me and get me an A in my physics classes.

 

[silverpig]

Originally posted by: Heisenberg

Originally posted by: silverpig
Light takes 8 years round trip. You travel at 99.9% light speed, you do the trip in 1/0.999 of 8 = 1.001001001 years from earth's perspective. To you in the ship this would be 8/14.1 = 0.567 years.

So you basically travel 8 ly in 0.567 years

This doesn't violate relativity though

I agree, but you have to be careful about how you word things. To YOU on the ship, the trip would still take 8 years. It's not like you'd see your watch suddenly run slow as you sped up. To everyone on earth, it would also take 8 years, but you'd have only aged 0.567 years to them when you returned.

Also, you have to keep in mind that the person on the ship is in two different intertial frames: one on the way, and a different one on the way back. Since special relativity deals with inertial frames moving w/respect to each other at uniform speed, you really have to look at the time dilation from the Earth's viewpoint.

Nope. You fvcked that up dude

To you on the ship it would only take 0.567 years. As in I am biologically 22 years old, and if I went on this trip I would biologically be 22.567 years old when I got back. My watch would have ticked off 0.567 years. On earth, 8.something years will have passed. They will see me travelling for 8 years, and they will see me as a biologically 22.567 year old guy with a watch that is about 7.5 years slow on his wrist.

Me on ship - trip is .5 yrs
peeps on earth - trip is 8 yrs

 

[Heisenberg]

Originally posted by: silverpig

Originally posted by: Heisenberg

Originally posted by: silverpig
Light takes 8 years round trip. You travel at 99.9% light speed, you do the trip in 1/0.999 of 8 = 1.001001001 years from earth's perspective. To you in the ship this would be 8/14.1 = 0.567 years.

So you basically travel 8 ly in 0.567 years

This doesn't violate relativity though

I agree, but you have to be careful about how you word things. To YOU on the ship, the trip would still take 8 years. It's not like you'd see your watch suddenly run slow as you sped up. To everyone on earth, it would also take 8 years, but you'd have only aged 0.567 years to them when you returned.

Also, you have to keep in mind that the person on the ship is in two different intertial frames: one on the way, and a different one on the way back. Since special relativity deals with inertial frames moving w/respect to each other at uniform speed, you really have to look at the time dilation from the Earth's viewpoint.

Nope. You fvcked that up dude

To you on the ship it would only take 0.567 years. As in I am biologically 22 years old, and if I went on this trip I would biologically be 22.567 years old when I got back. My watch would have ticked off 0.567 years. On earth, 8.something years will have passed. They will see me travelling for 8 years, and they will see me as a biologically 22.567 year old guy with a watch that is about 7.5 years slow on his wrist.

Me on ship - trip is .5 yrs
peeps on earth - trip is 8 yrs

Yeah, I forgot to take into account the length contraction you would see from the spaceship. That "fixes" the paradox so that you only experience the 0.567 years while the 8 years pass on earth.

 

[Eli]

Ok.. so.. Is "time travel" possible? lol

 

[Heisenberg]

Originally posted by: Eli
Ok.. so.. Is "time travel" possible? lol

Into the future? Sure. Just strap a big rocket on and go 0.999c for a while. When you come back to earth, you will have "traveled" into the future.

 

[hjo3]

Originally posted by: Eli
Ok.. so.. Is "time travel" possible? lol

Sure, but only forward.

 

[silverpig]

Originally posted by: Eli
Ok.. so.. Is "time travel" possible? lol

Sure is. We're doing it right now

But yeah, you can easily go into the future if you go fast enough. Going into the past would require faster than light travel, and there are a lot of theories on how to do this, but unfortunately they require massive rotating black holes, super spaceships, and people immune to the ripping apart side effect of intense gravitational fields

 

[TuxDave]

Originally posted by: hjo3

Originally posted by: Eli
Ok.. so.. Is "time travel" possible? lol

Sure, but only forward.

Depends... do we live in a Star Trek universe?

 

[Heisenberg]

Originally posted by: Eli
Ahh.. Yeah. That's what I thought.

Wow.. What a bizzare concept.. So did Einstein just whip that out of his ass one day or what? lol

Sort of. All of this weirdness follows from the speed of light being the ultimate speed limit. That's really what Einstein just whipped out one day.

 

[DWW]

Originally posted by: hjo3

Originally posted by: Eli
Ok.. so.. Is "time travel" possible? lol

Sure, but only forward.

And its only relative to earth. In that time is not absolute in the universe so you aren't really going further than normal, given your context (going speed near c). Right? Just trying to confuse Eli more

 

[Descartes]

Originally posted by: Heisenberg

Originally posted by: Eli
Ahh.. Yeah. That's what I thought.

Wow.. What a bizzare concept.. So did Einstein just whip that out of his ass one day or what? lol

Sort of. All of this weirdness follows from the speed of light being the ultimate speed limit. That's really what Einstein just whipped out one day.

This is always said, but wouldn't some credit to Faraday, Maxwell, and Roemer have to be given here? Understandably, Einstein included the postulate that "no information can travel faster than 'c'", but that wasn't much more than a derivation of what was already known. Right? Einstein pushed the issue into new light (pun intended), but I wouldn't say he just whipped it out. Without Lorentz, Newton, Faraday, Maxwell, Roemer, Galileo, etc. to supplicate he wouldn't have had relativity either special or general.

imo.

 

[Vic]

Good discussion. Not to change gears, but one problem I see is that everyone is assuming you could accelerate from 0 to 0.99c instantaneously. Not so.
Someone correct my figures if I'm wrong (I used the equation of Acceleration = (Final Velocity) - (Original Velocity) / Time), but at a constant acceleration of 2G's (which would be quite uncomfortable over time), it would take 177 days 10 hours and 39 minutes to reach 0.99c. A similar deceleration would be required before reaching Proxima Centauri, and then another acceleration and deceleration on the return trip. All this could throw all those figures off quite a bit.

 

[Heisenberg]

Originally posted by: Descartes

Originally posted by: Heisenberg

Originally posted by: Eli
Ahh.. Yeah. That's what I thought.

Wow.. What a bizzare concept.. So did Einstein just whip that out of his ass one day or what? lol

Sort of. All of this weirdness follows from the speed of light being the ultimate speed limit. That's really what Einstein just whipped out one day.

This is always said, but wouldn't some credit to Faraday, Maxwell, and Roemer have to be given here? Understandably, Einstein included the postulate that "no information can travel faster than 'c'", but that wasn't much more than a derivation of what was already known. Right? Einstein pushed the issue into new light (pun intended), but I wouldn't say he just whipped it out. Without Lorentz, Newton, Faraday, Maxwell, Roemer, Galileo, etc. to supplicate he wouldn't have had relativity either special or general.

imo.

Yeah, I was being a bit facetious. Special relativity was mostly invented to expain the behavior of electric and magnetic fields, which of course Faraday and Maxwell had a huge part in.

 

[silverpig]

Originally posted by: Descartes

Originally posted by: Heisenberg

Originally posted by: Eli
Ahh.. Yeah. That's what I thought.

Wow.. What a bizzare concept.. So did Einstein just whip that out of his ass one day or what? lol

Sort of. All of this weirdness follows from the speed of light being the ultimate speed limit. That's really what Einstein just whipped out one day.

This is always said, but wouldn't some credit to Faraday, Maxwell, and Roemer have to be given here? Understandably, Einstein included the postulate that "no information can travel faster than 'c'", but that wasn't much more than a derivation of what was already known. Right? Einstein pushed the issue into new light (pun intended), but I wouldn't say he just whipped it out. Without Lorentz, Newton, Faraday, Maxwell, Roemer, Galileo, etc. to supplicate he wouldn't have had relativity either special or general.

imo.

Meh I don't know about Maxwell. Of the 4 "Maxwell's equations" he only modified one of them (added time dependence of a magnetic field or something IIRC). The other 3 were known

 

[Descartes]

Originally posted by: Vic
Good discussion. Not to change gears, but one problem I see is that everyone is assuming you could accelerate from 0 to 0.99c instantaneously. Not so.
Someone correct my figures if I'm wrong (I used the equation of Acceleration = (Final Velocity) - (Original Velocity) / Time), but at a constant acceleration of 2G's (which would be quite uncomfortable over time), it would take 177 days 10 hours and 39 minutes to reach 0.99c. A similar deceleration would be required before reaching Proxima Centauri, and then another acceleration and deceleration on the return trip. All this could throw all those figures off quite a bit.

This is a thought experiment, so assumptions are going to be made. No one is considering the fact that E=mc^2 and would almost certainly preclude us going 0.99c anyway.

 

[silverpig]

Originally posted by: Vic
Good discussion. Not to change gears, but one problem I see is that everyone is assuming you could accelerate from 0 to 0.99c instantaneously. Not so.
Someone correct my figures if I'm wrong (I used the equation of Acceleration = (Final Velocity) - (Original Velocity) / Time), but at a constant acceleration of 2G's (which would be quite uncomfortable over time), it would take 177 days 10 hours and 39 minutes to reach 0.99c. A similar deceleration would be required before reaching Proxima Centauri, and then another acceleration and deceleration on the return trip. All this could throw all those figures off quite a bit.

But first you'd need to build the ship, and before that you'd need some other stuff...

You're right, but this was mainly a mathematics of relativity question I'd say.

I say beam me up scotty... you're there instantaneously

 

[Descartes]

Originally posted by: silverpig

Originally posted by: Descartes

Originally posted by: Heisenberg

Originally posted by: Eli
Ahh.. Yeah. That's what I thought.

Wow.. What a bizzare concept.. So did Einstein just whip that out of his ass one day or what? lol

Sort of. All of this weirdness follows from the speed of light being the ultimate speed limit. That's really what Einstein just whipped out one day.

This is always said, but wouldn't some credit to Faraday, Maxwell, and Roemer have to be given here? Understandably, Einstein included the postulate that "no information can travel faster than 'c'", but that wasn't much more than a derivation of what was already known. Right? Einstein pushed the issue into new light (pun intended), but I wouldn't say he just whipped it out. Without Lorentz, Newton, Faraday, Maxwell, Roemer, Galileo, etc. to supplicate he wouldn't have had relativity either special or general.

imo.

Meh I don't know about Maxwell. Of the 4 "Maxwell's equations" he only modified one of them (added time dependence of a magnetic field or something IIRC). The other 3 were known

Known in what way? That's something of a Platonic view, no? The phenomenon might have been known, but he provided the quantitative footing same as Newton to mechanics. It's been a long while since I read any treatise on Maxwell, so color me a bright shade of moron if I speak falsely.