# Special Relativity II

#### topsquark

Forum Staff
This is a post by
GatheringKnowledge

2. According to Special Relativity, time doesn't flow for any frame, which is moving at 100% c. It means, that from perspective of a photon, which is moving from point A to point B, it's journey becomes instant - photon reaches destination at point B in the same moment, when it's being emitted in point A. According to mainstream science, photons do not age and don't have any history, that could be tracked. From our perspective, it takes around 8m 20s for light, to pass the distance between the Sun and Earth - but from the perspective of a photon, which is emitted by the Sun, it takes 0m 0s, to travel all the way to Earth. And now my question is: what would happen with a photon, which was emitted by the Sun in the direction of Earth, if we would place a polarization filter on it's way, soon after it was emitted from the Sun?

If time doesn't exist at 100% c, then light would have to reach the Earth's surface without being polarized - as the filter wasn't placed on the photon's path at the moment of emission. But if it would reach Earth, while being polarized, it would mean, that each photon has it's own age and a specific history, which we can possibly track in time - so it will be clear, that time has to flow at 100% c...

#### topsquark

Forum Staff
The light will not have a time lapse in its own reference frame. So, according to the photon it takes no time to hit the filter and then no time to get to the surface of the Earth.

What do you mean by the phrase "so it will be clear,k that time has to flow at 100% c" ?

-Dan

#### GatheringKnowledge

The light will not have a time lapse in its own reference frame. So, according to the photon it takes no time to hit the filter and then no time to get to the surface of the Earth.
In the moment of the photon emission, there's no filter on it's way to Earth - we are placing an obstacle in a choosen moment of those 8m 20s, which from our perspective light needs, to pass the distance Sun-Earth...

What do you mean by the phrase "so it will be clear,k that time has to flow at 100% c" ?
If light would arrive at Earth polarized, it would mean, that we can learn about the history of a photon, which was emitted in moment A, passed the polarization filter at moment B and reached the surface of Earth at C - and history requires the existence of a timeline...

May I ask, why did you cut my thread into pieces? Now I have to jump around 3 different threads, to discuss my own questions, which fit into a single category (light and relative motion)...

I wanted to make a separate thread for General Relativity and now it seems, that I will probably have to make 3 different ones: one about shell theorem, second about cheerios effect and surface tension and third about gravitational expulsion of plasma ...

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#### Woody

Experiments of this kind (inserting a filter after emission, but before detection, in "our" time frame) have been performed.

If you think about a particle traveling at nearly the speed of light, the problem goes away,
the filter is inserted a tiny fraction of time after emission (in the time frame of the particle).
As the emitted particle get closer to the speed of light that tiny fraction of time (in the particles time frame) gets even smaller.
In the limit, as the particle approaches the speed of light, the time of insertion of the filter (in the particles time frame) approaches zero.

I think that Topsquark was trying to make responding easier for us (the respondents) to answer each of your points separately,
rather than having to point out which point we are responding to...

topsquark

#### GatheringKnowledge

Experiments of this kind (inserting a filter after emission, but before detection, in "our" time frame) have been performed.

If you think about a particle traveling at nearly the speed of light, the problem goes away,
the filter is inserted a tiny fraction of time after emission (in the time frame of the particle).
As the emitted particle get closer to the speed of light that tiny fraction of time (in the particles time frame) gets even smaller.
In the limit, as the particle approaches the speed of light, the time of insertion of the filter (in the particles time frame) approaches zero.
Yes, if we talk about particle travelling nearly at the speed of light, then the problem goes away. That's why I'm talking about a photon, which doesn't accelerate, but moves at 100% of c from the very moment of emission.

#### Woody

The concepts of time and distance become problematical when viewed from the reference frame of a photon traveling at "c".
However causality must remain sacrosanct.
There are three events "experienced" by the photon; emission, polarization, detection (in that order).
The observed positioning of those events, in both time and space, will depend on the relative velocities of the emitter, the polariser, the detector and also the observer,
but the order must remain the same.
For a photon the time from emission to polarization is zero and the time from polarization to detection is zero,
note that this indicates the distance (in the reference frame of the photon) is also zero.

topsquark

#### GatheringKnowledge

The concepts of time and distance become problematical when viewed from the reference frame of a photon traveling at "c".
However causality must remain sacrosanct.
There are three events "experienced" by the photon; emission, polarization, detection (in that order).
The observed positioning of those events, in both time and space, will depend on the relative velocities of the emitter, the polariser, the detector and also the observer,
but the order must remain the same.
For a photon the time from emission to polarization is zero and the time from polarization to detection is zero,
note that this indicates the distance (in the reference frame of the photon) is also zero.
Yes - I know, that things become quite problematic, if we try to discuss the frame of a photon. This is exactly why I'm discussing it

In this case, I see 2 issues with your explanation... Let's say, that for someone on Earth timeline of events looks like this: A is for Sun emitting a photon, B is the polarization and C is the arrival at Earth's surface. At the time of event A there's no polarization filter on the photon's path - let's say, that we place it 4m 10s after the emission...

1 issue: if for a photon it takes zero time, to travel any distance, then it's arrival at Earth (C) has to be completely determined in the moment of it's emission on the Sun (A). Shortly speaking, for any frame moving at 100%c events A & C are simultaneus. At the time of A, there's no filter on the photon's path, so event C is being determined before we set the event B to happen between events A and C. And of course, since for a photon there's no time interval between events, then the final outcome can't change any time after the emission...

2 issue: 0 divided by any number gives always 0. You can't "insert" event B to the timeline of simultaneus events A & C, as there's no timeline at all. All what you can do, is to add event B to simltaneus events A & C and make them all happen simultaneusly. You seem to be a smart guy, so you probably know well, that there's no specific order, for anything, what happens simultaneusly. Events happen in order OR they happen simultaneusly - you just can't have it both ways. If for a photon order of events has to be maintained due to causality, then there has to be a specific timeline for it's frame. Sorry, there's no way around, as both options exclude eachother...

This is how SRT can't survive a confrontation with simple logic - and logic is above everything else in physics. If a theory leads to results, which deny common sense, then it simply can't be correct... There are no paradoxes in observable universe...

#### benit13

This is a post by
GatheringKnowledge

2. According to Special Relativity, time doesn't flow for any frame, which is moving at 100% c.
I don't think this is true. Yes, an object travelling at the speed of light can travel to any point in the universe instantaneously and time becomes a meaningless concept for photons because of this, but this is mainly because the travel distance contracts to zero at the speed of light. However, local observers in a reference frame will always observe their own clocks to tick at the usual rate within local reference frames, regardless of its speed relative to everyone else.

Imagine if you were travelling at the speed of light and then you slow down by a very tiny amount. Suddenly, the travel distance will become non-zero and the time taken to reach the destination will be non-zero and can be measured. External observers will also start to be able to observe your clock ticking at a slower rate. However, as far as the operation of your own watch goes, you will still see it ticking at the same rate as it always has; no change.

#### GatheringKnowledge

I don't think this is true. Yes, an object travelling at the speed of light can travel to any point in the universe instantaneously and time becomes a meaningless concept for photons because of this, but this is mainly because the travel distance contracts to zero at the speed of light. However, local observers in a reference frame will always observe their own clocks to tick at the usual rate within local reference frames, regardless of its speed relative to everyone else.

Imagine if you were travelling at the speed of light and then you slow down by a very tiny amount. Suddenly, the travel distance will become non-zero and the time taken to reach the destination will be non-zero and can be measured. External observers will also start to be able to observe your clock ticking at a slower rate. However, as far as the operation of your own watch goes, you will still see it ticking at the same rate as it always has; no change.
Ok, you're right: intead "According to Special Relativity, time doesn't flow for any frame, which is moving at 100% c", I should say: "According to Special Relativity, time doesn't flow for a photon.".

#### topsquark

Forum Staff
I once heard about the "time flow" for a photon and it basically said that time has no meaning for a photon (or any other massless particle.) However I should have pointed out from the start that massive objects and massless objects are very much not the same thing. Massless particles are sort of a singularity of sorts for QM. They have a completely different symmetry group from massive particles. I'm not sure we can really discuss time as it is "measured" for a photon's "inertial frame."

I'll let others more in the know to decide if this makes a difference in the conversation.

-Dan