The Naked Scientists

The Naked Scientists Forum

Author Topic: The Physical consequences of light speed travel: Would you age?  (Read 7877 times)

Offline NB27

  • First timers
  • *
  • Posts: 1
    • View Profile
From what I understand, time stops at the speed of light. If, hypothetically, someone was able to travel at the speed of light.... would they cease to age?


 

Offline PmbPhy

  • Neilep Level Member
  • ******
  • Posts: 2768
  • Thanked: 38 times
    • View Profile
Quote from: NB27
From what I understand, time stops at the speed of light. If, hypothetically, someone was able to travel at the speed of light.... would they cease to age?
Welcome to the forum!

That's a common misconception. Since nothing can ever travel at the speed of light then it's meaningless to say that anything will age at a rate for which time stops.
 

Offline flr

  • Sr. Member
  • ****
  • Posts: 302
  • Thanked: 2 times
    • View Profile
Quote
Since nothing can ever travel at the speed of light ....

What about photons? Aren't they at the speed of light?
 

Offline JohnDuffield

  • Sr. Member
  • ****
  • Posts: 488
  • Thanked: 1 times
    • View Profile
From what I understand, time stops at the speed of light. If, hypothetically, someone was able to travel at the speed of light.... would they cease to age?
Yes. Note that whilst PmbPhy correctly said that you can't actually travel at the speed of light, you can in theory travel at a speed that is arbitrarily close to the speed of light.
 

Offline Bill S

  • Neilep Level Member
  • ******
  • Posts: 1830
  • Thanked: 12 times
    • View Profile
This seems like another variation on the question: “Do photons experience time?”  It usually elicits some strong feelings, but probably cannot be resolved beyond saying that we have no physical model that covers that scenario. 

As John points out, “you can in theory travel at a speed that is arbitrarily close to the speed of light.”  However, as it would require infinite energy to accelerate a massive object to “c”, and take “infinite time” to get there, arbitrarily close is still infinitely far away, so no meaningful comparison can be made.
 

Offline JohnDuffield

  • Sr. Member
  • ****
  • Posts: 488
  • Thanked: 1 times
    • View Profile
Actually Bill, there's an easy way to travel at the speed of light.

I kid ye not. It doesn't even take any energy.
 

Offline Pecos_Bill

  • Sr. Member
  • ****
  • Posts: 334
    • View Profile
As far as I know, you would have infinite mass at the speed of light. Tell me whether God can make a stone so heavy that he cannot pick it up. Then I will tell you whether time stops at the speed of light.
 

Offline jeffreyH

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 3927
  • Thanked: 55 times
  • The graviton sucks
    • View Profile
Actually Bill, there's an easy way to travel at the speed of light.

I kid ye not. It doesn't even take any energy.

Slow light down in a super cool medium?
 

Offline Bill S

  • Neilep Level Member
  • ******
  • Posts: 1830
  • Thanked: 12 times
    • View Profile
Quote from: John
Actually Bill, there's an easy way to travel at the speed of light.

It can be argued that we are all travelling through spacetime at the speed of light, always.

Quote from: Jeffrey
Slow light down in a super cool medium?

Not if you have to travel in the same medium.  :)

 

Offline Pecos_Bill

  • Sr. Member
  • ****
  • Posts: 334
    • View Profile
The effect of time is to separate events. If time stopped, how would you know it?
 

Offline PmbPhy

  • Neilep Level Member
  • ******
  • Posts: 2768
  • Thanked: 38 times
    • View Profile
Quote from: flr
What about photons? Aren't they at the speed of light?
They travel at the speed of light but it can't be said that photons age. Aging is either a chemical or a biological process, neither of which can take place is a frame of reference that is traveling at the speed of light relative to any inertial frame of reference.
 

Offline Bill S

  • Neilep Level Member
  • ******
  • Posts: 1830
  • Thanked: 12 times
    • View Profile
Quote from: Pete
They travel at the speed of light but it can't be said that photons age. Aging is either a chemical or a biological process, neither of which can take place is a frame of reference that is traveling at the speed of light relative to any inertial frame of reference.

I understand, and agree with, what you are saying here, Pete; but the nit-picker in me will not be stilled.  You are assigning a frame of reference to a photon; can you do that?  Are you distinguishing between a F of R and an inertial frame?
 

Offline jeffreyH

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 3927
  • Thanked: 55 times
  • The graviton sucks
    • View Profile
You have to assume a frame of reference for the photon. This frame changes during interactions with other fields. It does not have constant attributes so a scalar proportionality needs to be applied as with Lorentz transforms for any other type of mass. This becomes most apparent at the event horizon of a black hole. If we do not consider the frame of reference of the photon then how can we describe the effects on light? Using only the wavelength and energy of the photon is not enough in my opinion. How does the field of a slowed photon behave? Is the interaction of light with matter also slowed down?

EDIT: For an observer moving at a significant fraction of the speed of light and with increased mass/energy see an x-ray as visible light? This is one to ponder.
« Last Edit: 10/01/2015 17:00:16 by jeffreyH »
 

Offline PmbPhy

  • Neilep Level Member
  • ******
  • Posts: 2768
  • Thanked: 38 times
    • View Profile
Quote from: Bill S
I understand, and agree with, what you are saying here, Pete; but the nit-picker in me will not be stilled.  You are assigning a frame of reference to a photon; can you do that? 
No. That's the problem.
 

Offline Bill S

  • Neilep Level Member
  • ******
  • Posts: 1830
  • Thanked: 12 times
    • View Profile
Quote from: Pete
Aging is either a chemical or a biological process, neither of which can take place is a frame of reference that is traveling at the speed of light.....

Sorry Pete, still nit-picking. :)

you refer to a "frame of reference that is traveling at the speed of light".  A photon is the only thing that can travel at the speed of light; so are you not assigning a F of R to a photon.

Actually, this is not just a case of nit-picking.  Elsewhere, I have been involved in a thread in which I was arguing that we cannot assign a F of R to a photon, so I'm keen to be aware of anything that might seem to be a flaw in my reasoning. 
 

Offline Bill S

  • Neilep Level Member
  • ******
  • Posts: 1830
  • Thanked: 12 times
    • View Profile
Quote from: Pecos_Bill
The effect of time is to separate events.


Each event must differ in some respect from every other event, so what you are saying is that time emerges from change. 

Quote
If time stopped, how would you know it?

The acquisition and recognition of knowledge involves change, so if change stops (a prerequisite of time’s stopping) there would be no knowledge of anything.
 

Offline jeffreyH

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 3927
  • Thanked: 55 times
  • The graviton sucks
    • View Profile
Just another note on this. The spectrum of the photon will be shifted for an observer traveling at a significant proportion of the speed of light. Those photons arriving coincident with a direction exactly perpendicular to the direction of travel should preserve their energy, wavelength and frequency. Photon approaching from in front will be blue shifted and those following will be red shifted. It should then follow that visible light that follows the traveler will now be in the infra-red range. X-rays may then near but not reach the visible range of the spectrum but ultra-violet light may now be visible. Approaching x-rays will shift into a range approaching the energy of cosmic rays. I have done no mathematics on this so do not know the exact shape of the spectrum in such a situation. It will vary around a 360 degree plane and with the angle of the approaching photon.
 

Offline King Amada

  • First timers
  • *
  • Posts: 1
    • View Profile
Its Very Simple, just record a video of light travelling and play it, then forward to increase the speed of light and rewind to slow the speed of light.
 

Offline Bill S

  • Neilep Level Member
  • ******
  • Posts: 1830
  • Thanked: 12 times
    • View Profile
Quote from: King Amada
Its Very Simple, just record a video of light travelling and play it, then forward to increase the speed of light and rewind to slow the speed of light.

Hi KA, welcome.

How would you do that?  As I understand it, the light would be visible to your camera only when the photons entered the lense, after which it would no longer be travelling.
 

Offline PmbPhy

  • Neilep Level Member
  • ******
  • Posts: 2768
  • Thanked: 38 times
    • View Profile
Its Very Simple, just record a video of light travelling and play it, then forward to increase the speed of light and rewind to slow the speed of light.
That doesn't really have anything to do with faster than light motion. It's also not possible to record a beam of light in that way. What you're doing is recording is the light off of an object which is standing still or moving at speeds less than c.
 

Offline JohnDuffield

  • Sr. Member
  • ****
  • Posts: 488
  • Thanked: 1 times
    • View Profile
Slow light down in a super cool medium?
Nope. It's even easier than that.

...This becomes most apparent at the event horizon of a black hole...
Close but no cigar. What's the coordinate speed of light at the black hole event horizon? And if you fall into a black hole from a hypothetical "infinite" distance, what's your speed alleged to be when you allegedly cross that event horizon?
 

Offline jeffreyH

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 3927
  • Thanked: 55 times
  • The graviton sucks
    • View Profile
Slow light down in a super cool medium?
Nope. It's even easier than that.

...This becomes most apparent at the event horizon of a black hole...
Close but no cigar. What's the coordinate speed of light at the black hole event horizon? And if you fall into a black hole from a hypothetical "infinite" distance, what's your speed alleged to be when you allegedly cross that event horizon?

What you are saying is that falling into the event horizon of a black hole achieves superluminal speed with no involvement of energy. Right? You are really saying that superluminal speed is achieved before the event horizon. I have been down this path but there are severe problems with this approach.
 

Offline Pseudoscience-is-malarkey

  • Full Member
  • ***
  • Posts: 96
    • View Profile
The complexities of interstellar/intergalactic travel is rarely illustrated in science fiction.

IN STAR WARS, HOW DO PEOPLE COMMUNICATE WITH OTHER PEOPLE AT DIFFERENT PARTS OF THE GALAXY IN REAL TIME????????????????????????????????
 

Offline PmbPhy

  • Neilep Level Member
  • ******
  • Posts: 2768
  • Thanked: 38 times
    • View Profile
The complexities of interstellar/intergalactic travel is rarely illustrated in science fiction.

IN STAR WARS, HOW DO PEOPLE COMMUNICATE WITH OTHER PEOPLE AT DIFFERENT PARTS OF THE GALAXY IN REAL TIME????????????????????????????????
Real-Time communication that far away is not possible in nature. That's merely sci-fi which doesn't adhere to the laws of nature.
 

The Naked Scientists Forum


 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums
 
Login
Login with username, password and session length