Noob question: If you travel as fast as light, time freezes so

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SUMMARY

This discussion clarifies misconceptions surrounding the concept of traveling at the speed of light and its implications on time perception. It establishes that no object with mass can reach light speed, as doing so would require infinite energy due to mass increase, as per Einstein's theory of relativity. Photons, while traveling at light speed, do not experience time in the same way as massive objects; they do not "freeze" in time but rather maintain a constant speed relative to all observers. The conversation emphasizes that the frame of reference for photons is nonsensical, and understanding relativistic effects requires a focus on speeds approaching, but never reaching, the speed of light.

PREREQUISITES
  • Understanding of Einstein's Special Theory of Relativity
  • Familiarity with the concept of mass-energy equivalence (E=mc²)
  • Basic knowledge of gravitational effects on light (gravitational redshift)
  • Awareness of the concept of reference frames in physics
NEXT STEPS
  • Study the implications of relativistic speeds on time dilation and length contraction
  • Explore gravitational effects on light in detail, focusing on general relativity
  • Investigate the concept of mass increase at relativistic speeds
  • Learn about the behavior of particles near black holes and event horizons
USEFUL FOR

Students of physics, educators explaining relativity, and anyone interested in the fundamental principles of light and time in the context of modern physics.

  • #31
But we can get to another galaxies. When Universe will be expanding faster and faster, you will cross the event horizon in finite time. In Big Rip scenario, it happens to ALL observers.
 
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  • #32
Dmitry67 said:
But we can get to another galaxies. When Universe will be expanding faster and faster, you will cross the event horizon in finite time. In Big Rip scenario, it happens to ALL observers.
I am not sure if any of these thoughts are connected, or if they follow from my comment.
 
  • #33
DaveC426913 said:
Why do you think this is counter-intuitive? Why would you expect the Moon, which is moving at ~1km/s to move on the same path as light, which is moving at 300,000km/s?

Dave, thanks for your reply, the putting green analogy was very clear. I wasn't thinking of anything being counter-intuitive, it was more of a semantics problem, I guess, which you straightened out. Thanks!
 
  • #34
Because as expansion accelerates because of the Dark Energy, distant galaxy which is not beyond the cosmological horizon now can be behind it in the future.
 
  • #35
Dmitry67 said:
Because as expansion accelerates because of the Dark Energy, distant galaxy which is not beyond the cosmological horizon now can be behind it in the future.

Is your quote feature not working?
 
  • #36
DaveC426913 said:
Is your quote feature not working?

I'm going to guess that Dmitry67 is probably messing with you because he knows you'll correct him each time; he's probably trying to see how long you'll go before you stop. I don't know him/her, but as I said, that's my guess.

As for the initial question concerning 'time freezing', I'd like to add my two cents which is just confirming what has already been similarly stated. Let's say you 'could' travel with the photon, for the sake of making an analogy (CAUTION: I say the following 'very loosely'): try not to think of time as 'freezing' for the photon, instead let's say that it does not really 'apply' anymore, if you will. 'At' the speed of light, the 'rest of the world' will 'freeze' because you are traveling 'at the speed of time'. I am NOT saying that you can travel backwards in time however, because we would start violating the law of entropy. To you, at speed c, traveling a great distance would seem to happen instantaneously.

I now subject my words to the PF guillotine as I press the "Submit Reply" button... :wink:
 
  • #37
rod_worth said:
As for the initial question concerning 'time freezing', I'd like to add my two cents which is just confirming what has already been similarly stated. Let's say you 'could' travel with the photon, for the sake of making an analogy (CAUTION: I say the following 'very loosely'): try not to think of time as 'freezing' for the photon, instead let's say that it does not really 'apply' anymore, if you will. 'At' the speed of light, the 'rest of the world' will 'freeze' because you are traveling 'at the speed of time'. I am NOT saying that you can travel backwards in time however, because we would start violating the law of entropy. To you, at speed c, traveling a great distance would seem to happen instantaneously.

I now subject my words to the PF guillotine as I press the "Submit Reply" button... :wink:

It's like walking on eggshells, in'it? :wink:

What we do here is talk about what happens as you approach arbitrarily close to the limit of c.

As you approach c, the universe will undergo length contraction in your direction of motion. Arbitrarily close to c, the universe will be contracted (along your direction of motion) by a commensurately large amount.

One can see that, in order to reach c, one must find themselves in a universe that is infinitely thin - a plane. Another way of looking at it is that they must, in fact, be at all points (along the direction their travel) at the same time.


And for special bonus points, try calculating the frequency of radiation that you'd be pelted with due to Doppler shift...
 
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  • #38
DaveC426913 said:
And for special bonus points, try calculating the frequency of radiation that you'd be pelted with due to Doppler shift...

Correct me if I'm wrong, but the relativistic Doppler effect as v -> c, would be:

f = (lim v->c)f0*sqrt([1+B]/[1-B])

which would be a frequency approaching infinity. I wouldn't be concerned about being 'pelted' by 'frequency' as much as I would the infinite amount of energy associated with it (E=hf).
 
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  • #39
rod_worth said:
Correct me if I'm wrong, but the relativistic Doppler effect as v -> c, would be:

f = (lim v->c)f0*sqrt([1+B]/[1-B])

which would be a frequency approaching infinity. I wouldn't be concerned about being 'pelted' by 'frequency' as much as I would the infinite amount of energy associated with it (E=hf).

Precisely. :smile:
 
  • #40
DaveC426913 said:
Precisely. :smile:

Yay bonus points! :biggrin:
 
  • #41
a spaceship theoretically could be light (photons) because of the spacetime warpage. I was reading something about that lately. Are they wrong or what?
 
  • #42
filegraphy said:
a spaceship theoretically could be light (photons) because of the spacetime warpage. I was reading something about that lately. Are they wrong or what?

About what? Making a spaceship out of light? Tricky.
 
  • #43
Sorry it was a typo i meant if a spaceship and light had a race light would be beat by the spaceship because of spacetime warpage.
 
  • #44
Even in flat spacetime the light would win.
 
  • #45
Do we know what the engine of light is? I mean what causes it to travel?
 
  • #46
Light does not have or need an "engine". In the context you mean, engines are intended to accelerate a mass relative to something else. They have nothing to do with velocity, or travel.

Photons have velocity. They do not accelerate, or decelerate; once in motion, they tend to stay in motion, and the universe does not resist them.

Apparent deceleration in more-dense media (water vs air vs vacuum) is a product of the interaction of photons with the medias parent particles; there is a time delay as the light interacts with these things (photons are being created and destroyed), which causes an apparent decrease in net observed speeds (time between light energy entering the media and exiting the other side). The photons themselves are always traveling at c.
 
  • #47
Thanks for the reply talk2glenn. I appreciate the response. I do understand the constant nature of light. I was actually wondering if there were an understanding of why light moves? I realize that this may not yet be fully understood. I suspect not, but are there any theories?
 
  • #48
Prairie said:
Thanks for the reply talk2glenn. I appreciate the response. I do understand the constant nature of light. I was actually wondering if there were an understanding of why light moves? I realize that this may not yet be fully understood. I suspect not, but are there any theories?

The more appropriate question is: why does everything else not move at c? c is the "natural" state of things unemcumbered by mass. What is it about mass that slows things down?
 
  • #49
Doh... Thanks DaveC, I think I see. I'll probably be back with other questions.

Edit: Can I assume that the release of energy is an attempt to return to a natural state?
 
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  • #50
Prairie said:
Doh... Thanks DaveC, I think I see. I'll probably be back with other questions.

Edit: Can I assume that the release of energy is an attempt to return to a natural state?
No. Make no such assumption. We are postulating wildly here.
 
  • #51
Sorry, my bad. Are there any readings, or google or forum searches that might help me understand this relationship better? Thanks. I'd finally gotten around to reading some texts on the evolution of stars and my interest in the properties of light is tweaking my curiosity.
 
  • #52
Prairie said:
I was actually wondering if there were an understanding of why light moves? I realize that this may not yet be fully understood. I suspect not, but are there any theories?
Yes, there is a groundbreaking new theory called Maxwell's equations which explains the propagation of light in terms of the behavior of electric and magnetic fields.

Light is very well understood scientifically. Current theories accurately predict all known behaviors of light.
 
  • #53
Fair enough... lol. I don't know how to ask the question really.
 

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