Alpha centuri .4 light year relative to who?

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The discussion centers on the relativistic travel to Alpha Centauri, which is approximately 4 light years away from Earth. When traveling at 99.99999% the speed of light (c), the time experienced on Earth would be slightly over 4 years, specifically around 4 years and 13 seconds, while the time onboard the spacecraft would be approximately 16 hours. The conversation also highlights the significant challenges of accelerating to such high speeds, noting that achieving 99.9% of c at 1G acceleration would take one to two months, but reaching 99.99999% of c would require much higher accelerations, potentially exceeding 71,000 gees, which is detrimental to human health.

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

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
 
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matttan said:
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.
 


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.
 


Nabeshin said:
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 that's what I mean. So the time on Earth measured is 4 years?
 


matttan said:
Yeah that's 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!)
 


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.
 


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


DaveC426913 said:
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 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?
 
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  • #10


HallsofIvy said:
Does that include decelerating to a stop at alpha centauri or do you just "blow on by"?
Declerating.
 
  • #11


DaveC426913 said:
Declerating.

DaveC426913 said:
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 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.
 
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  • #12


qraal said:
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.
 

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