If time slows down as velocity approaches C

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Discussion Overview

The discussion centers on the implications of time dilation as an object approaches the speed of light, specifically addressing what occurs at the speed of light itself, particularly for massless particles like photons. Participants explore theoretical concepts related to time measurement, reference frames, and the nature of time for objects traveling at light speed.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants question what happens to the concept of time for a massless object traveling at the speed of light, suggesting that time may not exist in that frame of reference.
  • Others argue that while time appears to slow down for moving observers compared to stationary ones, the experience of time for the moving observer remains unchanged.
  • A participant proposes that a reference frame cannot exist where a massless particle is at rest, referencing Einstein's postulate that light travels at the speed of light in all frames.
  • Some contributions suggest that the passage of time has no meaning for a photon, as it exists everywhere in spacetime along its path.
  • There are conflicting views on whether time can be measured for objects moving at light speed, with some asserting that it cannot be measured while others maintain that it can be observed from different reference frames.

Areas of Agreement / Disagreement

Participants express multiple competing views regarding the nature of time at light speed, with no consensus reached on whether time exists or can be measured for massless particles. The discussion remains unresolved with various interpretations presented.

Contextual Notes

Participants highlight limitations in defining time for massless particles and the implications of reference frames, but do not resolve these complexities. The discussion reflects ongoing uncertainty about the nature of time in extreme relativistic contexts.

ecneicS
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I sense this question has been asked to death in these forums so sorry if I'm giving you a sense of Dejavu.

If the relative time of a moving object begins to slow as it APPROACHES the speed of light compared to another reference point, then what happens to the relative time when a moving object IS traveling at the speed of light, ie. a photon?
 
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ecneicS said:
I sense this question has been asked to death in these forums so sorry if I'm giving you a sense of Dejavu.

If the relative time of a moving object begins to slow as it APPROACHES the speed of light compared to another reference point, then what happens to the relative time when a moving object IS traveling at the speed of light, ie. a photon?

See What does the world look like in a frame of reference moving at the speed of light? (FAQ written by PF Mentor bcrowell.)
 
So does time for a massless object traveling at v not exist when v = c? If so, how can it have a velocity?
 
ecneicS said:
So does time for a massless object traveling at v not exist when v = c? If so, how can it have a velocity?

When we say time exists, we mean that we can measure it with a clock. I can use a clock to measure how much time it takes for light to get from point A to point B. When we say that time doesn't exist for a ray of light, what we mean is that the ray of light isn't a clock, so it can't measure elapsed time in its own frame of reference.
 
bcrowell said:
When we say time exists, we mean that we can measure it with a clock. I can use a clock to measure how much time it takes for light to get from point A to point B. When we say that time doesn't exist for a ray of light, what we mean is that the ray of light isn't a clock, so it can't measure elapsed time in its own frame of reference.

Thank you. I'm going to write that down. Is this the equivelant to what you are saying? We can measure time in a frame of reference only when there is matter (ie a clock) that is at rest in accordance to that frame of reference?
 
If you travel at the speed of light you still see time moving by at the same rate for you, but an observer watching you at zero velocity will notice time passing by at an undefined (infinitely large) rate as observed by you. so the fact that if you have a clock in ur reference frame which is moving at speed c you can measure time does not make time a meaningful quantity for you.
imagine taking a movie and then playing it at infinite speed, that's how an object at the speed of light will observe the universe.
 
ardie said:
If you travel at the speed of light you still see time moving by at the same rate for you, but an observer watching you at zero velocity will notice time passing by at an undefined (infinitely large) rate as observed by you. so the fact that if you have a clock in ur reference frame which is moving at speed c you can measure time does not make time a meaningful quantity for you.
imagine taking a movie and then playing it at infinite speed, that's how an object at the speed of light will observe the universe.


No. Time slows down as you move faster.
 
i stand corrected. the time will appear to move slower for you compared to the stationary world, but you will see time for the sationary observers pass by at an infinately high rate.
let me make it simpler for you
imagine two twins, one of them goes on a spaceshuttle traveling at the speed of light to Mars and back on a journey that takes 20 years. once the traveling twin is back he is the same age, but the older twin has watched the other twin travel for 20 years. so the traveling twin has observed the surrounding (stationary) world pass by at an infinitely high rate.
 
i know I am getting a bit too excited about this but einstein once mentioned, that if the hand of god operates at the speed of light, you will not notice it or what it does to your life
 
  • #10
ardie said:
i stand corrected. the time will appear to move slower for you compared to the stationary world, but you will see time for the sationary observers pass by at an infinately high rate.

Time never moves slower in your reference frame. You measure time as ticking slower in another observer's frame who is not at rest relative to you. So if there is a stationary observer relative to you that means you will measure time as ticking normally for that observer i.e. at the same rate as your own clock. The only time the time dilation would be infinite, if time dilation could even be defined in such a situation, is when the gamma factor blows up which is when the relative velocity of the other observer is v = c which we know is not possible.
 
  • #11
ardie said:
i stand corrected. the time will appear to move slower for you compared to the stationary world, but you will see time for the sationary observers pass by at an infinately high rate.
let me make it simpler for you
imagine two twins, one of them goes on a spaceshuttle traveling at the speed of light to Mars and back on a journey that takes 20 years. once the traveling twin is back he is the same age, but the older twin has watched the other twin travel for 20 years. so the traveling twin has observed the surrounding (stationary) world pass by at an infinitely high rate.

Thank you but I understand the basic principle you are attempting to explain. I want to know what happens when something IS going the speed of light, not approaching. All massless particles travel at the speed of light. My question is in a frame of reference where a massless particle is at rest, does the definition of time break down? Does time in this frame of reference exist when v=c? I feel it does not.
 
  • #12
ecneics said:
I want to know what happens when something IS going the speed of light, not approaching. All massless particles trave

What happens if you assume 2+2=5? This may sound a little flip, but there is a serious point here.
 
  • #13
pervect said:
What happens if you assume 2+2=5? This may sound a little flip, but there is a serious point here.

Hahaha thank you. I have missed out on something that has just become blatantly obvious to me. A reference frame cannot exist where a massless particle is at rest according to Einstein's postulate that light travels at the speed of light in ALL reference frames. Considering a reference frame that I am looking into is rather like saying what if 2+2=5. It doesn't, enough said.
 
  • #14
ecneicS said:
Thank you but I understand the basic principle you are attempting to explain. I want to know what happens when something IS going the speed of light, not approaching. All massless particles travel at the speed of light. My question is in a frame of reference where a massless particle is at rest, does the definition of time break down? Does time in this frame of reference exist when v=c? I feel it does not.

There is no frame of reference for a massless particle (eg photon) simply because it cannot be held in a state of rest. It cannot accelerate, and thus cannot ever arrive into the same frame of any inertial entity.

My opinion is that the passage of time has no meaning for a photon, as it coexists everywhere in spacetime along its propagational path. It passes thru space and time only per the vantage of material entity, because a body of rest mass possesses a specific frame of reference and thus experiences the passage of time.

GrayGhost
 
  • #15
WannabeNewton, i recommend you read the whole thread and carefully before posting.

ardie said:
If you travel at the speed of light you still see time moving by at the same rate for you, but an observer watching you at zero velocity will notice time passing by at an undefined (infinitely large) rate as observed by you.

and ecneics, time will pass by at the same rate regardless of what speed you travel at, as observed by you. your clock will allways tick a second as the time it takes to count 1001 or something of the same length.
the example i gave you is a countering paradox that requires us to change our definition of light travel. it tells us that time is a meaningless quantity for the photon, because say you traveled at the speed of light to Mars and back, this trip will take 0 seconds for you, so how can you have ever taken the trip? how would you know or prove you have traveled that distance?
i never gave you an example as you approach c, i gave you the bottomline, if u travel at c, there will be problems all around the universe...
 
  • #16
ardie said:
If you travel at the speed of light [...]
An observer can't travel at the speed of light.
 

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