Time Travelling at Speed of Light: What is My Time?

  • Context: Graduate 
  • Thread starter Thread starter Madhu R
  • Start date Start date
  • Tags Tags
    Time
Click For Summary

Discussion Overview

The discussion revolves around the concept of time perception while traveling at or near the speed of light, exploring implications of special relativity, including time dilation, the speed of light, and the behavior of light beams from different perspectives.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant suggests that traveling at the speed of light results in their time stopping, leading to confusion about experiencing two different times for light beams traveling in opposite directions.
  • Another participant advises considering travel close to the speed of light instead of at light speed, emphasizing the impossibility of the latter.
  • A third participant notes that no observer can travel at the speed of light and references Einstein's thought-experiment, explaining that observers moving at different speeds will perceive time differently but agree on the speed of light.
  • One participant proposes that if traveling at half the speed of light, their clock would run slower, leading to a calculation of light speed that seems inconsistent when considering beams traveling in opposite directions.
  • Another participant points out the importance of length contraction and the relativity of simultaneity, arguing that relativity encompasses more than just time dilation.
  • A later reply challenges the assumption that light speed in different directions relates to the observer's speed, clarifying that all observers measure the speed of light as constant regardless of their motion.

Areas of Agreement / Disagreement

Participants express differing views on the implications of traveling at or near the speed of light, with no consensus reached on the interpretation of time and light speed in this context.

Contextual Notes

Participants reference concepts such as the Lorentz transform, length contraction, and the relativity of simultaneity, indicating that the discussion is complex and dependent on these principles.

Madhu R
Messages
2
Reaction score
0
If I am traveling at the speed of light, I see a beam of light traveling in the same direction not moving. In other words, at the speed of light my time stops. But I would see another beam of light passing in the opposite direction traveling at the speed that is double the speed of light (?), or I would have to think that my time is flowing in the negative direction. Which is my time? Do I have two different times, one for each beam of light?
 
Physics news on Phys.org
Instead of traveling at the speed of light (which you can't), try thinking about traveling close to the speed of light.
 
No observer can travel at the speed of light.

This is the Einstein thought-experiment from his early years - he realized that it violates Faraday's Law of Induction, and hence is not possible.

But you can have an observer at rest, and another traveling at 0.99999c; they would both agree that the light passing in each direction is traveling at the same speed: they both are going at c.

And looking at each other each of you would see the other as running slow ... but looking at your own clock, everything is working fine. And the other guy (whichever one he is) will say that his clock is running fine as well.
 
It does not matter. Let us say I am traveling at half the speed of light. So my clock is slower by a factor of 0.5. And as per that that clock the speed of the first beam, which is traveling in the same direction, would calculate to c. But, if I you use the same clock for the other beam, which is traveling in the opposite direction, the speed would be 1.5 times c (?)
 
You are missing length contraction and the relativity of simultaneity, all of which have to be considered. Relativity is not just time dilation.

What you need to look at is the full Lorentz transform. It is easy to show that the Lorentz transform leaves c unchanged.
 
You seem to assume that lightspeed in different directions is some how related to your speed, like automobiles velocity addition and subtraction. That's not what happens.

Everybody observes the local speed of light at c regardless of their direction or the direction of the light.

Velocity addition and subtraction is explained here:

http://en.wikipedia.org/wiki/Relati...locities_formula#Special_theory_of_relativity
 

Similar threads

  • · Replies 26 ·
Replies
26
Views
960
  • · Replies 93 ·
4
Replies
93
Views
6K
  • · Replies 51 ·
2
Replies
51
Views
5K
  • · Replies 11 ·
Replies
11
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 42 ·
2
Replies
42
Views
3K
  • · Replies 51 ·
2
Replies
51
Views
5K
  • · Replies 11 ·
Replies
11
Views
1K
  • · Replies 26 ·
Replies
26
Views
2K
  • · Replies 5 ·
Replies
5
Views
2K