Alpha centuri.....4 light year relative to who?

[matttan]

Hi,

Here it goes.

Suppose it takes 4 light years to get to alpha centuri.

So if I could travel at 99.99999% the speed of light and the people on earth remains stationary(as in moving very slowly which is << C).

So does my clock shows 4 years when I get to alpha centuri or the clock on the earth shows 4 years.

I am a high school student so if possible avoid any technical explanation

Thanks

[berkeman]

Hi,

Here it goes.

Suppose it takes 4 light years to get to alpha centuri.

So if I could travel at 99.99999% the speed of light and the people on earth remains stationary(as in moving very slowly which is << C).

So does my clock shows 4 light years when I get to alpha centuri or the clock on the earth shows 4 light years.

I am a high school student so if possible avoid any technical explanation

Thanks

A light year is a distance, not a time. A light year is the distance that light travels in a year.

Could you please rephrase your question, so that times are in years, and distances are in light years? Thanks.

[Nabeshin]

Uhh, assuming (which I think you mean to) years instead of light years, the trip takes about sixteen hours for an observer moving at 99.99999.

[matttan]

Uhh, assuming (which I think you mean to) years instead of light years, the trip takes about sixteen hours for an observer moving at 99.99999.

Yeah thats what I mean. So the time on earth measured is 4 years?

[JesseM]

Yeah thats what I mean. So the time on earth measured is 4 years?
Yes, if we assume the distance from Earth to Alpha Centauri is exactly 4 light years in Earth's frame, and the ship is moving at 0.9999999c in Earth's frame, the time in Earth's frame is 4/0.9999999 years which is just a smidge over 4 years (around 4 years and 13 seconds!)

[qraal]

The time onboard ship would be almost 16 hours.

A problem arises because accelerating to that speed takes a lot of distance & time or very high acceleration. If you did it in 1 hour of ship-time the acceleration would be over 71,000 gees - very unhealthy for all on board. Even accelerating for a year the acceleration required would be over 8 gees.

[DaveC426913]

The time onboard ship would be almost 16 hours.

A problem arises because accelerating to that speed takes a lot of distance & time or very high acceleration. If you did it in 1 hour of ship-time the acceleration would be over 71,000 gees - very unhealthy for all on board. Even accelerating for a year the acceleration required would be over 8 gees.

Well, 99.99999% of c might be tough but I'd calced a way back that getting to 99.9% c only takes a month or two at 1G. I'll have to check my numbers again.


Ah right. I was looking at travelling to Gliese 581 (http://www.davesbrain.ca/science/gliese/index.html), which is 20 light years away and 6 years subjective. So a month or two of acceleration is small change.

[HallsofIvy]

Does that include decelerating to a stop at alpha centauri or do you just "blow on by"?

[qraal]

Well, 99.99999% of c might be tough but I'd calced a way back that getting to 99.9% c only takes a month or two at 1G. I'll have to check my numbers again.


Ah right. I was looking at travelling to Gliese 581 (http://www.davesbrain.ca/science/gliese/index.html), which is 20 light years away and 6 years subjective. So a month or two of acceleration is small change.

You figured it out, Dave?

[DaveC426913]

Does that include decelerating to a stop at alpha centauri or do you just "blow on by"?Declerating.

[qraal]

Declerating.

Well, 99.99999% of c might be tough but I'd calced a way back that getting to 99.9% c only takes a month or two at 1G. I'll have to check my numbers again.


Ah right. I was looking at travelling to Gliese 581 (http://www.davesbrain.ca/science/gliese/index.html), which is 20 light years away and 6 years subjective. So a month or two of acceleration is small change.

Dave, just how did you compute that? Reaching a rapidity equal to c at 1 gee takes a year of subjective time, and that's only a speed of 0.76 c. Getting to 0.999c - a rapidity of 3.8 c - takes somewhat higher gees to cram into a few months.

[DaveC426913]

Dave, just how did you compute that? Reaching a rapidity equal to c at 1 gee takes a year of subjective time, and that's only a speed of 0.76 c. Getting to 0.999c - a rapidity of 3.8 c - takes somewhat higher gees to cram into a few months.

You know what? Now I'm not sure.