How would you age at the speed of light?

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Offline ultimatebeast

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How would you age at the speed of light?
« on: 07/01/2013 22:55:43 »
I was wondering if one were to travel at the speed of light, how fast or slow would they age. Would they age at the same speed as on Earth because the speed of light is relative or would they age slower due to time dilation thanks for the replies
« Last Edit: 25/01/2013 17:15:01 by JP »

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Offline RD

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« Last Edit: 07/01/2013 23:43:53 by RD »

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Offline Pmb

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Re: How would you age at the speed of light
« Reply #2 on: 08/01/2013 01:55:24 »
I was wondering if one were to travel at the speed of light, how fast or slow would they age. Would they age at the same speed as on Earth because the speed of light is relative or would they age slower due to time dilation thanks for the replies
Since its impossible to travel at the speed of light the question is without meaning .. or to be more precise, there is no answer.

In any case, when speaking of aging one has to ask with respect to what clock one is aging with reference to.
« Last Edit: 08/01/2013 01:57:07 by Pmb »

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Offline Airthumbs

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Re: How would you age at the speed of light
« Reply #3 on: 08/01/2013 04:39:09 »
Nothing is impossible just highly improbable.... therefore in the extremely unlikely event it is possible to travel at the speed of light, say by switching off the Higs field for example, then I would be saying hello to me again?
Any intelligent fool can make things bigger and more complex... It takes a touch of genius - and a lot of courage to move in the opposite direction. (Einstein)

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Offline evan_au

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Re: How would you age at the speed of light
« Reply #4 on: 08/01/2013 08:53:18 »
If you were traveling "Very Fast*" in a straight line with no acceleration, an observer (say, on Earth) seeing you pass would think that you aged more slowly than them. http://en.wikipedia.org/wiki/Time_dilation#Relative_velocity_time_dilation

However, it gets a lot more complicated if you start on Earth and accelerate to reach the very fast speed, then decelerate and reverse to return to Earth.

*With our current understanding, "Very Fast" is always less than the speed of light in a vacuum. If your speed is closer to the speed of light, the observed rate of time passing gets closer to zero (from the viewpoint of an observer on Earth).

The Twin Paradox arises because from your viewpoint as a traveler, time for the observer on Earth is passing more slowly than for you.

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Offline AndroidNeox

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Re: How would you age at the speed of light
« Reply #5 on: 08/01/2013 20:45:41 »
To accelerate an object with non-zero rest mass, no matter how little, to the speed c would require infinite energy. Honestly, some things ARE impossible and this is one of them. That's probably why I've always been drawn to physics... it has some, few, rules that are utterly absolute for all observers under all possible circumstances. Most of these are represented as physical symmetries in Schrödinger’s equation. But, the speed c is an absolute constant for all observers under all circumstances.

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Offline Pmb

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Re: How would you age at the speed of light
« Reply #6 on: 09/01/2013 21:57:31 »
Nothing is impossible just highly improbable....
That's clearly wrong. and without basis. We know of things that are impossible, not merely improbably. E.g. suppose I were to ask you if it were  possible for you to be wrong? :)

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Offline flr

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Re: How would you age at the speed of light
« Reply #7 on: 10/01/2013 17:28:05 »
I was wondering if one were to travel at the speed of light, how fast or slow would they age. Would they age at the same speed as on Earth because the speed of light is relative or would they age slower due to time dilation thanks for the replies

The speed of light is not relative, it is an absolute constant.

Only photons (having zero rest mass) can travel at the speed of light.
It may be tempting to say that photons appear 'timeless' or 'out of time' or 'time does not flow for photons', because the faster an object move relative to us the more time dilated it appears to us.

However, that may be incorrect for the particular case of a photon.
In order to asses the time-dilation (and any other special relativity effects) one have to compare 2 frames of reference.
In other words I have to compare my local clock with photon's local clock and see (from my frame) how much the photon appears slowed down.
The problem is: it is unclear how to define a local clock (and ruler) for a photon. That means: you don't have a second frame (local to photon). If so, then we cannot apply the relativity to answer your  question.


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Offline ultimatebeast

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Re: How would you age at the speed of light
« Reply #8 on: 11/01/2013 17:19:48 »
Hi, you guuys thanks for all of the responses but I just want to know if someone traveled at the speed of light for 100 years how much he would age. Would he age the same or would he age slower. Thanks

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Offline Pmb

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Re: How would you age at the speed of light
« Reply #9 on: 11/01/2013 19:30:13 »
Hi, you guuys thanks for all of the responses but I just want to know if someone traveled at the speed of light for 100 years how much he would age. Would he age the same or would he age slower. Thanks
Since nobody can travel at the speed of light for any amount of time, your question has n answer.

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Offline Airthumbs

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Re: How would you age at the speed of light
« Reply #10 on: 14/01/2013 23:39:35 »
I could not help notice that my example of switching off the Higs field has been ignored.......  if the Higs field is responsible for giving objects mass and you switched it off somehow then surly that opens up new possibilities? 

PMB; if we fully understood our universe then I would fully agree with you........
« Last Edit: 15/01/2013 00:14:11 by Airthumbs »
Any intelligent fool can make things bigger and more complex... It takes a touch of genius - and a lot of courage to move in the opposite direction. (Einstein)

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Offline Pmb

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Re: How would you age at the speed of light
« Reply #11 on: 15/01/2013 00:51:32 »
I could not help notice that my example of switching off the Higs field has been ignored.......  if the Higs field is responsible for giving objects mass and you switched it off somehow then surly that opens up new possibilities? 

PMB; if we fully understood our universe then I would fully agree with you........
It is wrong to think that because we don't fully understand the universe that what we do understand must be wrong. Physicists assume certain thing when addressing questions and giving answers and those things are that the laws of physics as we know them are valid in the domain that they've been tested in. Again, there is no basis to assume that Nothing is impossible just highly improbable.... . How do you know that's true? Why would you assume that it's true? On what basis are you suggesting that the Higgs field could be switched off? Why would you believe that it could be done? If you say "Well we really don't know everything so we should not trust anything so that everything is possible" then that not only gets you nowhere but it also suggests that you're assuming that there is a Higgs field. I can, for the same reasons you've been using, that there's no such thing as a Higgs field.

My point is that it you say "We don't understand the universe" and take that to mean that all the laws of physics are wrong or shouldn't be trusted or could all be wrong then you might as well make up anything yhou wanted to without using any reason at all. Just whatever fantasy that comes to mind "could be true" etc.

That and $1.50 will get you cup of coffee.

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Offline AndroidNeox

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Re: How would you age at the speed of light
« Reply #12 on: 15/01/2013 01:48:49 »
Hi, you guuys thanks for all of the responses but I just want to know if someone traveled at the speed of light for 100 years how much he would age. Would he age the same or would he age slower. Thanks

The simple answer is, anything moving through space at c, equal to the speed of light in a vacuum, experiences zero time flow. If you were to travel at the speed of light, you would experience no time.

Actually, if you consider matter and energy in spacetime... EVERYTHING always travels through spacetime at c. An inertial observer, experiencing zero acceleration or force, will have a perspective that moves along its time axis at c, experiencing time at the maximum rate but no motion through space (from its own perspective). A light beam, or you, ultimatebeast, in this case, would be moving through space at c and would experience zero time.

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Offline Pmb

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Re: How would you age at the speed of light
« Reply #13 on: 15/01/2013 02:01:13 »
Quote from: AndroidNeox
The simple answer is, anything moving through space at c, equal to the speed of light in a vacuum, experiences zero time flow. If you were to travel at the speed of light, you would experience no time.
That kind of response is considered to be flawed since for it to have any meaning one would have to measure it and there’s now way to make a clock travel at the speed of light. Otherwise we’d have given this trivial answer long ago. Nobody and no thing can experience moving at the speed of light so the question is really meaningless. Especially since the OP referred to “someone” traveling at the speed of light. We know that no person can move at the speed of light. That’s why we’ve given the responses that we’ve given.

Quote from: AndroidNeox
Actually, if you consider matter and energy in spacetime... EVERYTHING always travels through spacetime at c.
That’s not true and is based on the misconception of a spacetime interval being identical to “distance” and then incorrectly calculating velocity by dividing a spacetime interval by the spacetime interval with a factor of c not canceling out. You can call the result you get  anything you’d like with the exception of “speed” or “velocity” or “traveling at c” since all these things already are well defined and already have well defined answers which are different than you’ve given. You just can’t say that its moving through spacetime with speed c. Those terms are already defined and cannot be redefined in the same breadth.

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Offline simplified

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Re: How would you age at the speed of light
« Reply #14 on: 15/01/2013 17:59:15 »
I was wondering if one were to travel at the speed of light, how fast or slow would they age. Would they age at the same speed as on Earth because the speed of light is relative or would they age slower due to time dilation thanks for the replies
Only your travel relatively of gravitational bodies makes your time slower.Your travel relatively of light doesn't make your time slower. :P

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Offline AndroidNeox

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Re: How would you age at the speed of light
« Reply #15 on: 15/01/2013 20:43:48 »
That’s not true and is based on the misconception of a spacetime interval being identical to “distance” and then incorrectly calculating velocity by dividing a spacetime interval by the spacetime interval with a factor of c not canceling out. You can call the result you get  anything you’d like with the exception of “speed” or “velocity” or “traveling at c” since all these things already are well defined and already have well defined answers which are different than you’ve given. You just can’t say that its moving through spacetime with speed c. Those terms are already defined and cannot be redefined in the same breadth.

The speed that we perceive to be c is a function of the angle between the space axis and the time axis. We only see a 3-space cross section of the 4-space trajectory and the tangent, distance/time = c.

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Offline Pmb

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Re: How would you age at the speed of light
« Reply #16 on: 15/01/2013 20:56:52 »
Quote from: AndroidNeox
The speed that we perceive to be c is a function of the angle between the space axis and the time axis. We only see a 3-space cross section of the 4-space trajectory and the tangent, distance/time = c.
Sorry but I can't even imagine what that's supposed to mean.

Speed is defined as distance traveled divided by the time it took to travel that distance. If you look at a spacetime diagram at a particle moving in one dimension then you will see a curve whose tangent is related to its speed. If the speed is constant then the speed of the object is defined as the run over the rise, that is to say that the speed is defined as the change in x divided by the change in t. Therefore for a straight line you select a point on the worldline of the particle. If the velocity is positive then you move to the right by an arbitrary amount dx. At the point where you moved to the right ended you now move straight up until you meet the curve. Let dt be the amount measured. Now divide dx by dt to get the speed of the particle, i.e. v = dx/dt. That value can only be c if the particle is moving at the speed of light.

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Offline AndroidNeox

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Re: How would you age at the speed of light
« Reply #17 on: 15/01/2013 21:00:23 »
c is a constant. That's not a property of light, that's a property of spacetime. It's a matter of geometry... the equal angle between space and time corresponds to c. You can think of it as a tangent a/b, distance/time. The angle always appears the same, to every observer. It's probably an inevitable artifact of observation... something about the way observation is structured, maybe. But, it's not something subject to variation. We do know enough about spacetime to understand that.

That's the whole magnificently cool thing about Relativity is that c is constant. That's why Einstein didn't like the name, "relativity", because the amazing thing he found out was that c is constant. That was the whole thing. Space and time have to adjust themselves to accommodate the fact but it's a fact for all observers at all times and has fascinating implications.

And, personally I would like to get the definition of "c" corrected to not be "the speed of light in a vacuum" but "the maximum speed at which information and energy can pass through space and equal to the constant velocity of all matter and energy through spacetime". Because, everything is always going through spacetime at c. The inertial observer's frame of reference moves along his/her time axis (world line) at the speed, c.

For inertial observers, the observer's time axis and world line are always coincident. For accelerating observers, their world line tips off-axis and they experience acceleration.

In 4-dimensional spacetime, everything always goes at c. Every particle with or without mass is moving at c along some trajectory in spacetime. That's why objects, like photons, moving at c though space cannot experience time... their total velocity is through space and the velocity component along the time axis is zero. The amount that time is slowed by velocity or acceleration are a matter of geometry... measured from the perspective of the observer. There is no universal or godlike perspective. Everything is relative to the observer's frame of reference. The amount of time slowing one inertial observer would see in a passing clock tower would be proportional to the cosine between the observer's world-line and the clock tower's time axis.

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Offline Pmb

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Re: How would you age at the speed of light
« Reply #18 on: 15/01/2013 21:13:09 »
Quote from: AndroidNeox
c is a constant. That's not a property of light, that's a property of spacetime. It's a matter of geometry... the equal angle between space and time corresponds to c.
I don’t know what angles you’re speaking of so I’ll assume that you’re talking about the angle a worldline of a particle moving at constant speed makes with the spatial or temporal axis. The only way for the angle between the worldline and the x axis to be equal to the worldline and the t axis is if either (1) you’re using units in which c = 1 or (2) you’ve scaled your time axis so that it doesn’t read t by ct. In that case if there is a worldline of a particle which passes through the origin and that worldline makes a 45 degree angle with respect to both axes them that particle is moving at the speed of light

Quote from: AndroidNeox
You can think of it as a tangent a/b, distance/time. The angle always appears the same, to every observer.
That is true only for null worldliness, i.e. for particles moving at the speed of light.

The point is that only particles that move at the speed of light have speed c. The other person was talking about the speed of objects in spacetime where I was speaking about the speed of objects in space. The term “speed of an object in spacetime” is meaningless. There are a few people here and there who like to say that all objects move at the speed of light in spacetime but no relativist would ever make such a statement. In fact when they hear that they sigh and say that its wrong.

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Offline Pmb

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Re: How would you age at the speed of light
« Reply #19 on: 15/01/2013 21:34:37 »
c is a constant. That's not a property of light, that's a property of spacetime.
I disagree. The properties of spacetime were selected so as to make the speed of light invariant.

By the way, the correct term is “invariant” not “constant”.

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Offline Airthumbs

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Re: How would you age at the speed of light
« Reply #20 on: 17/01/2013 02:39:04 »
PMB, I believe I owe you a coffee :)
Any intelligent fool can make things bigger and more complex... It takes a touch of genius - and a lot of courage to move in the opposite direction. (Einstein)

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Offline Pmb

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Re: How would you age at the speed of light
« Reply #21 on: 17/01/2013 06:07:10 »
PMB, I believe I owe you a coffee :)
Nice! I'll have a chocolate raspberry flavor, cream, sweet. The doughnuts are on me. :)

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Offline AndroidNeox

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Re: How would you age at the speed of light
« Reply #22 on: 23/01/2013 21:44:17 »
c is a constant. That's not a property of light, that's a property of spacetime.
I disagree. The properties of spacetime were selected so as to make the speed of light invariant.

You're saying that someone chose what the properties of spacetime would be to ensure c is the same for all observers?

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Offline Pmb

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Re: How would you age at the speed of light
« Reply #23 on: 25/01/2013 04:07:09 »
c is a constant. That's not a property of light, that's a property of spacetime.
I disagree. The properties of spacetime were selected so as to make the speed of light invariant.

You're saying that someone chose what the properties of spacetime would be to ensure c is the same for all observers?
In a manner of speaking, yes. The Lorentz transformation relationships transform events in S to events in S'. These transformations were designed so that c = invariant.

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Offline yor_on

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Re: How would you age at the speed of light
« Reply #24 on: 25/01/2013 17:06:28 »
But it is also a matter of practical experiments proving the theory Android :)
Otherwise I could argue that 'c' is 'c' 'all the way down', no proof presented..

A theory is a framework describing experiments correctly, as far as one knows at the time of the theory.

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Offline Humbleguy

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Re: How would you age at the speed of light?
« Reply #25 on: 02/02/2017 08:45:39 »
Sorry for bumping this very old thread, but after having read all the very scientifically correct answers, it bothers me that all answers dismiss the question of travelling at the speed of light (c) as being invalid. It is not, it is merely hypothetical.
The answer to the question is that as your relative velocity increases, your time slows down. This is not only your percieved time, but your actual physical time.
A common example is the atomic clocks of the satellites orbiting the earth. Even at their miniscule speeds in comparison to c, their clocks have to correct themselves. They simply run on a slower timeline than Earth.
So, if you travel in a spaceship and approach the speed of light, your timeline will also slow down. You will not notice. You will get up every morning, drink your coffee, go about your business. Everything will seem normal. But after having completed your 5-year-journey at 99.5% the speed of light and return home, you will notice that 50 years have passed on Earth. You have only aged five.
This gets more evident as you approach c, say 99.9% or 99.99%. Again, sitting in your spaceship, you would not notice.
Theoretically, if you DID manage to reach the speed of light, time would stand absolutely still for you, and a billion years on Earth would pass in an instant.
But, as many has pointed out above, as far as we know, it is utterly impossible for anything with a mass to reach the speed of light.
Kind regards.

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Offline puppypower

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Re: How would you age at the speed of light?
« Reply #26 on: 02/02/2017 12:15:18 »
At the speed of light, the universe will appear as a point-instant. At this point-instant discontinuity, the fabric of space-time will dissociate into separate threads of space and separate threads of time. The result is time and aging do not mean the same thing. 


If we followed a thread of time, that is separate from space, we could know the history of the entire universe in all places, simultaneously; omniscience. Time threads are not limited by space. If we followed a space thread, that is detached from time, we could be anywhere in the universe in zero time; omnipresence and worm holes.


These two attributes can be inferred from the point-instant universe we see. A point-instant universe allows us to be everywhere in the universe, at the same instant, and for all things to happen simultaneously, since all the universe overlaps as a point-instant. The result is we will not age in the normal sense of space-time, which localizes us in space-time, since we are distributed everywhere for all time.


If you look at the acceleration due to gravity, acceleration has the dimensions of d/t/t. In a dimensional sense, this is space-time; d-t, plus time t. Gravity can be modeled as extra time threads, embroidered into the fabric of space-time. This causes local space-time to pucker,  while also creating infinite simultaneity. This is reflected in universal superstructures, even though the speed of light is finite, they all maintain relative positioning.


We have never found the elusive gravitons, because we are looking for something in the form of d/t; energy. We are not looking for time threads, that lack the expected distance association of space-time; wavelength and frequency.


This is my own theory and does not reflect mainstream thinking. It is an extrapolation of the assumption that the speed of light reference, is the ground state of the universe. When time and space become dissociated, at the peed of light reference, entropy becomes infinite, since things are not limited by the speed of light traveling through space-time. This sets a potential for the second law. Universal entropy needs to increase as inertial references approaches the C ground state.


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Offline PmbPhy

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Re: How would you age at the speed of light?
« Reply #27 on: 02/02/2017 13:59:15 »
Quote from: Airthumbs
Nothing is impossible just highly improbable....
When people come here to ask a question they are assuming that the answer they get is in accordance with  the currently known laws of physics and that's the answer I gave him. Probability has nothing to do with this.

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Offline Bill S

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Re: How would you age at the speed of light?
« Reply #28 on: 03/02/2017 22:23:19 »
  This discussion about what happens to time at c is one that is likely to continue ad infinitum.  Even experts disagree about it.  My own view (buried somewhere in
 
http://www.askamathematician.com/2011/07/q-does-light-experience-time/?replytocom=558241#respond
 
is something akin to “we don’t know”).
 
Ethan Siegal’s article is worth reading.  He seems to be in no real doubt about his position.
 
https://medium.com/starts-with-a-bang/how-do-photons-experience-time-30c9bdeae3ae#.js1b0tnj7
 
There never was nothing.

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Offline yor_on

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Re: How would you age at the speed of light?
« Reply #29 on: 03/02/2017 22:55:58 »
Yeah Ethan seems to think of SpaceTime as one medium consisting of one spatial aspect, and one temporal. So moving spatially at a high speed then slows your clock, relative the rest of the universe/medium. what that takes as a given is that the universe is 'one medium', that's the ground from where it was constructed.You can go a different way using local measurements too, in that one this 'one medium' is left alone, instead you use the fact that your clock never lies to you. It will describe your aging exactly, no matter at what mass, or how fast you go. That's the principle we use doing experiments, and it is the one that gave us light as a constant called 'c'.
=

That's actually a problem with many theories. That they go out from what we see around us, and from that presume that what we see 'is'.  the way I see it Einstein understood this, but he wanted a 'whole universe' and so he looked for the 'fifth dimension' that would join it.
« Last Edit: 03/02/2017 23:08:24 by yor_on »
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Offline Bill_

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Re: How would you age at the speed of light?
« Reply #30 on: 10/02/2017 17:23:46 »
A quote from Einstein:

"...a paradox upon which I had already hit at the age of sixteen: If I pursue a beam of light with the velocity c (velocity of light in a vacuum), I should observe such a beam of light as an electromagnetic field at rest though spatially oscillating. There seems to be no such thing, however, neither on the basis of experience nor according to Maxwell's equations."

i.e. even light can't travel at the speed of light.

If you can have a light speed reference frame for a photon (many people say that's impossible but decline to give a proof) then in that frame the photon is created and destroyed at the same time and at the same place.

Concepts such as 'rest' and 'oscillating' do not apply to a photon which exists for zero time so the paradox is resolved.

If you could somehow travel at the speed of light  ( eg in a 'transporter beam' ) no time would pass for you and you wouldn't observe anything.

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Offline yor_on

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Re: How would you age at the speed of light?
« Reply #31 on: 10/02/2017 17:30:18 »
don't agree Bill. there is no frame of reference in where you can be at rest with light. and if that doesn't exist then there is no way to 'know' what a photon experience. what Einstein meant is not that there is no 'c'. Only that for you and me there would be no frame of reference in where we would find light being at rest with us. he's not tricky there, he's rather clear.
=

If you find a frame of reference in where you don't get a reflection from that mirror, aka being 'at rest' with light, I will be sorely interested reading you.
« Last Edit: 10/02/2017 17:32:39 by yor_on »
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Offline Bill_

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Re: How would you age at the speed of light?
« Reply #32 on: 10/02/2017 23:05:40 »
I'm not sure if this post is useful but I learned a fair amount making it.

don't agree Bill. there is no frame of reference in where you can be at rest with light. and if that doesn't exist then there is no way to 'know' what a photon experience. what Einstein meant is not that there is no 'c'. Only that for you and me there would be no frame of reference in where we would find light being at rest with us. he's not tricky there, he's rather clear.
=

If you find a frame of reference in where you don't get a reflection from that mirror, aka being 'at rest' with light, I will be sorely interested reading you.
I've just discovered I can now use hrefs; my quote was from newbielink:http://www.pitt.edu/~jdnorton/Goodies/Chasing_the_light/ [nonactive] which is worth reading for anyone interested in this topic.

I agree Einstein was clear, not tricky, which was why I used that quote.
I don't think Einstein meant that it was alright for him to do a thought experiment involving a frame of reference in which he would find light at rest, observing impossible physics, but not alright for you and me.

My 'light speed reference frame' has no paradoxes as far as I know. It exists for zero time (therefore has no defined velocity), has zero length and is intended for 'observation' of a particle which exists for zero time. It was intended only as another way to see the impossibility of travelling with and observing a photon.

In special relativity, the time a photon exists can be arbitrarily varied by selecting a suitable inertial frame. This is consistent with saying a photon exists for zero time but from an  inertial frame the time it exists is dilated by the factor 0 * 1/gamma i.e. 0/0 which is any arbitrary number. This singularity doesn't seem to bother physicists very much.
...if that doesn't exist then there is no way to 'know' what a photon experience
My understanding of relativity theory is that, as in Einstein's original thought experiment, there is no way consistent with known physics for a photon to exist for finite ie nonzero time. In zero time a photon cannot experience anything. All we can directly observe of photons is their creation and destruction.

If you find a frame of reference in where you don't get a reflection from that mirror, aka being 'at rest' with light, I will be sorely interested reading you.
Oh dear, no time to make that measurement... :(
I certainly shouldn't have said 'light speed reference frame.'
A reference frame that exists for zero time doesn't have a speed and I have to admit, is pretty useless.
However photons, existing for zero time, don't have a speed either.

'c' is calculated from observations of photon creation and destruction made from a suitable inertial frame. I don't suggest "there is no 'c'".





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Offline Bill S

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Re: How would you age at the speed of light?
« Reply #33 on: 10/02/2017 23:42:27 »
You stir some interesting thoughts, there, Bill.  I need to clarify one thing, though:

What is the difference between existing for zero time, and not existing?
There never was nothing.

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Online jeffreyH

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Re: How would you age at the speed of light?
« Reply #34 on: 11/02/2017 08:01:18 »
The problem is that photons travel through space. To be able to travel through space, time must pass, in order for a particle to have velocity. The photon also has a wavelength. Its energy varies when moving through a gravitational field. These changes cannot happen in zero time. If we consider the passage of time in an impossible reference frame then we are missing the point entirely.
Fixation on the Einstein papers is a good definition of OCD.

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Offline Bill_

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Re: How would you age at the speed of light?
« Reply #35 on: 11/02/2017 12:36:19 »
You stir some interesting thoughts, there, Bill.  I need to clarify one thing, though:

What is the difference between existing for zero time, and not existing?
I'll give a semiclassical response i.e. wrong, but maybe right enough to be useful...


If you consider a classical object moving at 1ft/sec, at one particular instant, for zero time, it will be exactly 2ft from its origin. If you observe only at this instant, you can't measure the object's speed.

This is reminiscent of the origins of calculus and is also related to Xeno's paradox, where he claimed IIRC that movement is impossible.

A photon could (maybe) be regarded as a configuration or particle which only exists for zero time as part of a continuing process.

The problem is that photons travel through space. To be able to travel through space, time must pass, in order for a particle to have velocity. The photon also has a wavelength. Its energy varies when moving through a gravitational field. These changes cannot happen in zero time. If we consider the passage of time in an impossible reference frame then we are missing the point entirely.
'If we consider the passage of time in an impossible reference frame then we are missing the point entirely.'

I would describe the reference frame as useless for making measurements but possibly of some value in understanding photons.
I've made clear one reason the reference frame is useless/impossible is because time doesn't pass.
I believe the observation that neutrinos have mass relied on the fact that time passes for neutrinos during flight; no time would pass if they were massless.

'[The photon's] energy varies when moving through a gravitational field.'

A photon's energy depends on the reference frame. Different frames give different energies without affecting the photon.


'These changes cannot happen in zero time.'
'To be able to travel through space, time must pass, in order for a particle to have velocity.'

In reply #32 I said there was a singularity involving gamma=0. From inertial reference frames this is seen as photons travelling at c with reference frame dependent lifetime, energy etc.
If these changes are changes in the photon rather than solely a result of choice of reference frames then time is passing for the photon and it has a velocity. As with the neutrino, the photon would have to have rest mass.


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Online jeffreyH

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Re: How would you age at the speed of light?
« Reply #36 on: 11/02/2017 12:49:21 »
In order to be slowed down by gravity, time must pass for the photon. It accelerates in a gravitational field. This is also a non inertial frame. The impossibility of the passage of time in  the frame of the photon has  to be a function of rest mass. A photon doesn't have rest mass.
« Last Edit: 11/02/2017 12:58:26 by jeffreyH »
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Offline Bill_

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Re: How would you age at the speed of light?
« Reply #37 on: 11/02/2017 14:04:30 »
In order to be slowed down by gravity time must pass for the photon. It accelerates in a gravitational field. This is also a non inertial frame.

According to the equivalence principle, experiments inside an accelerating rocket are equivalent to experiments in a gravitational field.

First use a reference frame which is accelerating with the rocket.
So... inside the rocket send a photon from a source at the base to a detector at the top.
A sensitive detector will find the photon has red shifted slightly. If relativistic effects are fully taken into account, the speed of the photon did not change.

Viewed from an inertial frame, when the photon reaches the detector, the detector is moving faster in the direction of the photon than the source was when the photon was emitted. Taking into account the detector's change of speed, it can be calculated that the photon has not red shifted. The speed of the photon did not change.

The energy of a photon is always dependent on the reference frame.


The impossibility of the passage of time in  the frame of the photon has  to be a function of rest mass. A photon doesn't have rest mass.

Clarify please.

I hope I've made clear that the 'frame of the photon' was only intended as a gedankenexperiment. :(


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Offline yor_on

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Re: How would you age at the speed of light?
« Reply #38 on: 11/02/2017 16:35:44 »
Actually, it's not mathematics, it's a fact. Try a two (way) mirror experiment yourself. you get 'c', that's where the mathematics come from.
=
Ah well, spelling and senility always f*s it up :)
« Last Edit: 11/02/2017 16:43:25 by yor_on »
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Offline Bill S

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Re: How would you age at the speed of light?
« Reply #39 on: 12/02/2017 12:51:54 »
Quote from: Bill
If you consider a classical object moving at 1ft/sec, at one particular instant, for zero time, it will be exactly 2ft from its origin. If you observe only at this instant, you can't measure the object's speed.
Even in principle, you can’t make am observation in zero time; so, like trying to work with the idea of a massive object travelling at c (apart from Einstein) this is a no-go situation.  In principle, you could make an observation that lasted for Planck’s time, and argue that that was not divisible, but that’s not the same as zero time. 
Quote
A photon could (maybe) be regarded as a configuration or particle which only exists for zero time as part of a continuing process.
This may be a mathematical “truth”, but in reality nothing can happen in zero time, and zero cannot ba a part of anything.  To be part of something, it must be something.
There never was nothing.

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Offline puppypower

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Re: How would you age at the speed of light?
« Reply #40 on: 12/02/2017 13:36:19 »
I was wondering if one were to travel at the speed of light, how fast or slow would they age. Would they age at the same speed as on Earth because the speed of light is relative or would they age slower due to time dilation thanks for the replies

One problem with answering this question is there is a system wide confusion with respect to how we define and measure time. We measure time with clocks, which are based on cycles, such as 12 noon to 12 noon, or Monday to Monday. However, this is not how time propagates. Time does not repeat itself like clocks or like vibrations from a cesium atom.


As an experiment, photograph yourself at noon today and then at noon tomorrow to see if you become totally refreshed like the clock. Time is about change, and not about the repeat cycling as expressed by clocks. The way we measure time, does not reflect the nature of time, leading to confusion.

As an analogy of this problem, say I wanted you to arrange all my sea shells by size, largest to smallest. Instead of using a meter stick, which how you should measure size, you decide to use a scale. Like a clock, a scale can be used to measure the shells, but it does not necessarily reflect the nature of size. You line up the shells based on weight, largest to smallest, which causes some the smaller but heavier shells, to be placed near the beginning. The result will be confusion, if I tell everyone look my shell collection, arranged by size.


Clocks slow and speed up due to relativity, but clocks cycle and time does not. If we measured my sea shells, outside with the scale on a windy day, this can impact the measured weight. However, it will have no impact if we had used a meter stick.

A better clock to measure time, would be something like the dead fish clock. This clock uses a dead fish, with time measured, based on the ever increasing odor from the decaying fish. Like the flow of time, the dead fish clock does not cycle, since we can't un-stink the fish. But also like time, the next fish we add to the clock, may not have the same stink profile as the previous. Just as each day moves forward in time in its own unique way, so each dead fish clock refill will be different.


The dead fish clock is an entropy clock. This type of clock better reflects the nature of time, than do cyclic clocks. Both time and entropy move in one direction; increase to the future, and both are reflected as change which can be different each time.


With a dead fish clock, heating and cooling the dead fish refill, will impact the rate of decay and therefore alter the flow of measured time. The same thin would also happen if we use relativity. The entropy will slow or speed up in time. I point this to show what happens when you measure time the way time flows. Cyclic clocks will not have the same parallel, since these clocks are modeled on waves; cycles.

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Offline Bill_

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Re: How would you age at the speed of light?
« Reply #41 on: 12/02/2017 18:33:36 »
If you consider a classical object moving at 1ft/sec, at one particular instant, for zero time, it will be exactly 2ft from its origin. If you observe only at this instant, you can't measure the object's speed.
Even in principle, you can’t make am observation in zero time; so, like trying to work with the idea of a massive object travelling at c (apart from Einstein) this is a no-go situation.  In principle, you could make an observation that lasted for Planck’s time, and argue that that was not divisible, but that’s not the same as zero time. 
I could have been clearer and said 'you can't measure the object's speed or any other property.' Classically I could say 'There is no known way to measure the object's speed but the object exists whether or not you observe or measure it.'

You originally asked
What is the difference between existing for zero time, and not existing?
As the (classical) object moves, at all times its exact distance is mappable to some point, at which it remains for zero time. Whether or not the object exists at these zero time instances is too deep a question for me.

A photon could (maybe) be regarded as a configuration or particle which only exists for zero time as part of a continuing process.
This may be a mathematical “truth”, but in reality nothing can happen in zero time, and zero cannot ba a part of anything.  To be part of something, it must be something.
I can't extract your intended meaning from that response.
From earlier:

In special relativity, the time a photon exists can be arbitrarily varied by selecting a suitable inertial frame. This is consistent with saying a photon exists for zero time but from an inertial frame the time it exists is dilated by the factor 0 * 1/gamma i.e. 0/0 which is any arbitrary number. This singularity doesn't seem to bother physicists very much.

i.e. the apparent non zero lifetime of a photon is a relativistic effect.

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Offline Bill S

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Re: How would you age at the speed of light?
« Reply #42 on: 12/02/2017 19:59:37 »
Quote from: Bill
'There is no known way to measure the object's speed but the object exists whether or not you observe or measure it.'
I’m happy to accept that objects exist when they are not being observed/measured.
Quote
As the (classical) object moves, at all times its exact distance is mappable to some point, at which it remains for zero time.

To make that claim, you would first have to establish that “zero time” exists as a physical entity.
Quote
I can't extract your intended meaning from that response.

John Barrow says this about mathematical existence:

“Gradually mathematicians lighted upon a new concept of existence.  Mathematical ‘existence’ meant only logical self-consistency and this neither required nor needed physical existence to complete it.  If a mathematician could write down a set of non-contradictory axioms and rules for deducing true statements from them, then those statements would be said to ‘exist’.”

 If there can be a profound difference between physical and mathematical “existence” then it seems reasonable to identify a similar difference between physical and mathematical “truth”.  When Barrow talks of “deducing true statements” from “non-contradictory axioms”, one has to wonder if the truth of these statements can always be maintained in the real world, or if they are just mathematically true. 

In many cases, especially those involving “nothing” or “infinity”, the latter seems, often, to be the case.
There never was nothing.

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Online jeffreyH

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Re: How would you age at the speed of light?
« Reply #43 on: 12/02/2017 21:04:43 »
Particles with zero rest mass must travel at the speed of light in a vacuum. Particles with rest mass resist change in direction or speed of motion. Acceleration applies to both direction and speed. For particles with rest mass the acceleration can be positive or negative. The question is does this apply in the same way for light in any choice of coordinates?
Fixation on the Einstein papers is a good definition of OCD.

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Offline Bill_

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Re: How would you age at the speed of light?
« Reply #44 on: 13/02/2017 15:00:28 »
Quote from: Bill
'There is no known way to measure the object's speed but the object exists whether or not you observe or measure it.'
I’m happy to accept that objects exist when they are not being observed/measured.
I only made that claim unequivocally for classical objects.
It's easier to follow this topic if you include hrefs e.g.
Classically I could say 'There is no known way to measure the object's speed but the object exists whether or not you observe or measure it.'

Quote
As the (classical) object moves, at all times its exact distance is mappable to some point, at which it remains for zero time.

To make that claim, you would first have to establish that “zero time” exists as a physical entity.
Why? I now claim that zero hedgehogs are present at each point. Do I have to establish that “zero hedgehogs” exists as a physical entity?
Quote
I can't extract your intended meaning from that response.

John Barrow says this about mathematical existence:

“Gradually mathematicians lighted upon a new concept of existence.  Mathematical ‘existence’ meant only logical self-consistency and this neither required nor needed physical existence to complete it.  If a mathematician could write down a set of non-contradictory axioms and rules for deducing true statements from them, then those statements would be said to ‘exist’.”

 If there can be a profound difference between physical and mathematical “existence” then it seems reasonable to identify a similar difference between physical and mathematical “truth”.  When Barrow talks of “deducing true statements” from “non-contradictory axioms”, one has to wonder if the truth of these statements can always be maintained in the real world, or if they are just mathematically true. 

In many cases, especially those involving “nothing” or “infinity”, the latter seems, often, to be the case.
'Wonder' and 'seem' are not evidence.


A photon could (maybe) be regarded as a configuration or particle which only exists for zero time as part of a continuing process.
This may be a mathematical “truth”, but in reality nothing can happen in zero time....
I still don't understand this. I stated earlier that nothing can happen in zero time. Is the mathematical “truth” different?


What is the difference between existing for zero time, and not existing?
Perhaps you could answer this:

It's generally agreed that for a photon, unlike a massive particle, time does not pass while it is, w.r.t. an inertial reference frame, apparently moving. Does the photon exist for zero time, or does it not exist or does it exist for finite time?

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Offline phyti

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Re: How would you age at the speed of light?
« Reply #45 on: 13/02/2017 17:21:30 »
I was wondering if one were to travel at the speed of light, how fast or slow would they age. Would they age at the same speed as on Earth because the speed of light is relative or would they age slower due to time dilation thanks for the replies
"If" doesn't require that it's a real possibility, just a speculation, or fantasy.
At light speed, the light clock stops working. All processes that depend on mediation via photons, chemistry, biology, etc. would cease. A state equivalent to death! No aging, no perception, nothing. Be careful what you wish for!
 

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Online jeffreyH

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Re: How would you age at the speed of light?
« Reply #46 on: 13/02/2017 17:42:29 »
I was wondering if one were to travel at the speed of light, how fast or slow would they age. Would they age at the same speed as on Earth because the speed of light is relative or would they age slower due to time dilation thanks for the replies
"If" doesn't require that it's a real possibility, just a speculation, or fantasy.
At light speed, the light clock stops working. All processes that depend on mediation via photons, chemistry, biology, etc. would cease. A state equivalent to death! No aging, no perception, nothing. Be careful what you wish for!

It would be the death of the universe since infinite energy would be required. Then everything would cease to exist. In its current form at least.
Fixation on the Einstein papers is a good definition of OCD.

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Offline Bill S

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Re: How would you age at the speed of light?
« Reply #47 on: 13/02/2017 20:39:55 »
Quote from: Jeffrey
Acceleration applies to both direction and speed. For particles with rest mass the acceleration can be positive or negative. The question is does this apply in the same way for light in any choice of coordinates?

Presumably it doesn’t apply to the invariant speed of light in a vacuum, and there seems to be a line of reasoning that argues that even when apparently slowed in a medium, light is still travelling at c.

The directional component may be a different matter, as light is manifestly diverted by gravity.

Did you have any particular coordinates in mind?
There never was nothing.

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Offline Janus

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Re: How would you age at the speed of light?
« Reply #48 on: 13/02/2017 21:07:39 »
I was wondering if one were to travel at the speed of light, how fast or slow would they age. Would they age at the same speed as on Earth because the speed of light is relative or would they age slower due to time dilation thanks for the replies
"If" doesn't require that it's a real possibility, just a speculation, or fantasy.
At light speed, the light clock stops working. All processes that depend on mediation via photons, chemistry, biology, etc. would cease. A state equivalent to death! No aging, no perception, nothing. Be careful what you wish for!
You can't say that.  Here's the problem, you can't extrapolate the time dilation formula to v=c.  At v=c the equation results in a division by 0 which is undefined.   You can say that the that the aging rate of our person approaches 0 as his speed approaches c, but you can say nothing of his aging rate at c.     Likewise, you can say that the energy required to increase the speed of mass approaches infinity as the speed of the mass approaches c, but you cannot say that this energy is infinite at c, because it too becomes undefined when v=c.

The problem with such questions is that they are asking you to apply a theory to an problem outside the domain of the theory.

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Offline yor_on

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Re: How would you age at the speed of light?
« Reply #49 on: 13/02/2017 21:40:51 »
What you make me think of' Bill, suggesting a 'photon' being 'at rest' using your example of a photon being of zero duration, is the one with energy/time aka HUP Time-Energy Uncertainty Relation    I don't think that idea will hold though, one reason is that it has a zero duration in one frame, that then means that it wasn't there at all, or you will have to change the definition of zero, another is the idea of that everything measurable in one frame somehow has to present itself in all other frames able to communicate with each other, that's about causality, what I think of as a logic. Introducing something from nothing is a logic that I'm uncomfortable with.
==

Maybe this one if you're mathematically inclined does light experience time?

Ps: hopefully this link works, I couldn't see it as I had to redo it, editing, so I'm not sure if it will work in all browsers.
Seems to work in mine though.

Better add that the last one is about a 'photons' rest frame, or lack of rest frame.
« Last Edit: 13/02/2017 22:03:24 by yor_on »
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