How do you calculate change in time at the speed of light?

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Discussion Overview

The discussion revolves around the calculation of time changes at relativistic speeds, particularly at or near the speed of light. Participants explore concepts such as time dilation, reference frames, and the perception of time by observers in different frames of reference.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants assert that one cannot experience time changes at the speed of light, emphasizing that time dilation is perceived by remote observers rather than the individual moving at high speeds.
  • There is a discussion about how time dilation affects perceptions of time for observers, with some suggesting that if one travels at .9c, their clock ticks normally while observers would perceive time differently.
  • One participant mentions that at .9c, the time dilation factor is approximately 2.3, while at .995c, it is about 10, indicating how time is perceived differently at these speeds.
  • Participants highlight the importance of specifying a frame of reference when discussing speeds like .9c, as it can lead to misunderstandings regarding observations and calculations.
  • There is a suggestion that when moving away from a galaxy at high speeds, it would appear to rotate slower due to relativistic effects, and this is supported by the Lorentz Transform.
  • Some participants discuss the distinction between time dilation and what one would actually see, suggesting that the relativistic Doppler effect should be considered for accurate observations.
  • There is a contention about the terminology used, with some participants arguing that phrases like "your body at the speed of light" are misleading and can lead to confusion in understanding the concepts being discussed.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of time dilation and its implications, with no clear consensus reached on the nuances of the concepts discussed. The conversation remains unresolved regarding the precise implications of time dilation and how it relates to observation.

Contextual Notes

Limitations include the need for clarity in terminology and the dependence on specific frames of reference for accurate calculations and observations. The discussion also highlights the complexity of relativistic effects and their interpretations.

quincy harman
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How do you calculate change in time at the speed of light?
 
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quincy harman said:
How do you calculate change in time at the speed of light?
You don't because (1) you can't GO at the speed of light and (2) there IS no change in your time as you speed up, so even if you are talking about an achievable .999999c, your clock still ticks at one second per second.

You are probably thinking of time dilation, which is not an experienced phenomena but rather something that is perceived by remote observers, not the one being observed.

For example, you, right now as you are reading this, are MASSIVELY time dilated according to an accelerated particle at CERN and mildly time dilated relative to a passing comet and not at all time dilated according to your chair. Do you feel any of these effects? Do you feel all of them at the same time? (that would be a good trick).
 
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That is exactly what I am talking about so you would observe everyone else moving slower? while your watch keeps ticking 1 second per second? and if you're traveling at .9 c for one hour how much time would have passed for people observing you? Would they be able to even see you? Would you appear frozen in time?
 
quincy harman said:
and if you're traveling at .9 c for one hour how much time would have passed for people observing you?
At .9c, the time dilation factor is about 2.3. So you would each see the other as moving at a little less than half speed.

At .995c, you'd be seeing a factor of 10.

Play with this calculator:
http://www.1728.org/reltivty.htm
 
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Cool thank you!
 
And keep in mind that "traveling at .9 c" is a meaningless statement by itself. You have to specify what you are using as a frame of reference. The assumption is that you mean .99c relative to an observer, but it's best to specify that.
 
phinds said:
And keep in mind that "traveling at .9 c" is a meaningless statement by itself. You have to specify what you are using as a frame of reference. The assumption is that you mean .99c relative to an observer, but it's best to specify that.
so if you're moving .99c away from the galaxy it would appear to be rotating slower?
 
quincy harman said:
so if you're moving .99c away from the galaxy it would appear to be rotating slower?
Yes. When you are moving relative to something that something always looks slower. At normal (human "normal" that is) the difference is negligible but at relativistic speeds you can use the Lorentz Transform to see the relationship
 
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The time affecting your body at speed of light is in relative to the observer for you your time is just normal for you but relatively slower for an observer.
 
  • #10
Athul Prem said:
The time affecting your body at speed of light is in relative to the observer for you your time is just normal for you but relatively slower for an observer.

"your body at speed of light" is ridiculous. Have you not read the rest of the posts in this thread?
 
  • #11
"...your body near the speed of light..." and it's sensical.
 
  • #12
The OP's question was about the calculated speed, so strictly speaking the time dilation formula is the right one to use. OTOH the words "seeing" and "appearing" have crept into the discussion at various points, so I'm just pointing out that if you want to know what you would actually see you should use the relativistic doppler formula, not the time dilation formula. The time dilation formula does not tell you what you would see as it does not take into account the light travel time to the observer. In particular, although traveling away from a galaxy at high speed you would see it rotating more slowly (also it would appear to be much closer/larger), whereas if you were traveling towards it you would see it rotating more quickly (and it would appear to be further away/smaller).
 
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  • #13
DaveC426913 said:
"...your body near the speed of light..." and it's sensical.
Well, of course it is, but I'm trying to help him see that sloppy terminology lead to (or stems from) sloppy thinking.
 

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