Alpha centuri .4 light year relative to who?

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Discussion Overview

The discussion revolves around the concept of time dilation and the experience of time for travelers moving at relativistic speeds, specifically in the context of traveling to Alpha Centauri, which is approximately 4 light years away. Participants explore the implications of traveling at 99.99999% the speed of light and how time is perceived differently for the traveler compared to observers on Earth.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants clarify that a light year is a measure of distance, not time, and suggest rephrasing the original question to avoid confusion.
  • One participant estimates that the trip would take about 16 hours for an observer traveling at 99.99999% the speed of light.
  • Another participant confirms that, in Earth's frame, the time measured would be just over 4 years, accounting for the speed of the ship.
  • Concerns are raised about the feasibility of accelerating to such high speeds, with one participant noting that achieving 99.99999% of the speed of light would require extreme acceleration, potentially harmful to passengers.
  • Participants discuss alternative scenarios, such as reaching 99.9% of the speed of light with a more manageable acceleration of 1G, and question the calculations involved in these scenarios.
  • There is a mention of the need to consider deceleration upon reaching Alpha Centauri, raising further questions about the journey's dynamics.
  • One participant expresses uncertainty about their calculations regarding the time required to reach relativistic speeds, indicating a lack of consensus on the specifics of the acceleration and time experienced by travelers.

Areas of Agreement / Disagreement

Participants generally agree on the relativistic effects of time dilation but express differing views on the specifics of acceleration, travel time, and the feasibility of reaching such speeds. The discussion remains unresolved regarding the exact calculations and implications of these scenarios.

Contextual Notes

Limitations include assumptions about constant acceleration, the effects of high g-forces on human passengers, and the complexities of relativistic physics that are not fully explored in the discussion.

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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