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

In summary, the conversation discussed the concept of time dilation and how it relates to traveling at the speed of light. It was explained that time dilation is not experienced by the person traveling, but rather perceived by observers. The conversation also touched on the idea of relativistic speed and how it affects the perception of time and objects. The importance of using specific terminology to avoid confusion was emphasized.
  • #1
quincy harman
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How do you calculate change in time at the speed of light?
 
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  • #2
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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  • #3
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?
 
  • #4
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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  • #5
Cool thank you!
 
  • #6
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.
 
  • #7
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?
 
  • #8
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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  • #9
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.
 

1. What is the formula for calculating change in time at the speed of light?

The formula for calculating change in time at the speed of light is Δt = Δx/c, where Δt represents the change in time, Δx represents the change in distance, and c represents the speed of light in a vacuum.

2. How does the theory of relativity affect the calculation of change in time at the speed of light?

The theory of relativity, specifically Einstein's theory of special relativity, states that time is relative to the observer's frame of reference. This means that the measurement of time can vary depending on the observer's relative motion. Therefore, when calculating change in time at the speed of light, we must consider the observer's frame of reference and the effects of time dilation and length contraction.

3. Can change in time be negative when calculating at the speed of light?

No, change in time cannot be negative when calculating at the speed of light. This is because the speed of light is a constant and cannot be exceeded, meaning that time can only move forward or remain constant. In other words, time cannot go backwards at the speed of light.

4. How does the concept of time dilation impact the calculation of change in time at the speed of light?

Time dilation is the effect of time passing more slowly for an object in motion compared to one at rest. This means that as an object approaches the speed of light, time for that object will appear to slow down for an observer. This must be taken into account when calculating change in time at the speed of light to accurately reflect the time experienced by the moving object.

5. Is the calculation of change in time at the speed of light affected by the direction of motion?

Yes, the calculation of change in time at the speed of light can be affected by the direction of motion. This is due to the fact that time dilation and length contraction are relative to the direction of motion. This means that an object moving in a certain direction may experience a different change in time compared to an object moving in the opposite direction at the same speed.

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