between3and26characterslon

30 minutes ago, swansont said:

Yes, and it takes more time for reasons that have been discussed.

Sure.

And the terminology you use, "virtual state, interaction, does not impart energy or momentum"

is different from some of the terminology others used, "bounces around, absorbed and re-emitted, bumps into"

On 2/11/2020 at 4:17 PM, StringJunky said:

The apparent slowdown is caused by the photon accumulating a delay time by briefly interacting with and being emitted from electrons as it passes through but at all times it is transmitted it travels at c.... there is never any acceleration.

On 2/11/2020 at 4:19 PM, iNow said:

No. The photon does not accelerate or slow down. It always travels at c, by definition. The "slowdown" is only in your perception due to (as StringJunky highlighted) the photon bouncing around and interacting with more stuff in the glass... It travels farther, basically.

On 2/11/2020 at 4:51 PM, iNow said:

If I travel from my home to the store in a straight line at 30 mph, it takes 10 minutes to get there. If I later travel from my home to the store using back roads and take several turns and go up and down some hills, but still do so at a speed of 30 mph, it takes me 20 minutes to get there. I was always traveling at 30 mph, though. I just went a greater distance to get there the 2nd time.

On 2/11/2020 at 5:12 PM, StringJunky said:

To elaborate: Photons interact/get absorbed permanently  with electrons when they have the right wavelength. Those that do will not pass through if they have, rendering the material opaque at those wavelengths when observed. With transparent material, like glass, photons in the visible spectrum don’t have the right wavelength to be absorbed by the electrons, so they are only absorbed briefly and then. re-emitted for a brief but finite time. The important thing to realise is that as it travels in between electrons it is moving at c. Each time it bumps  into an electron its total travel time is extended, hence, giving the appearance of slowing down.

6 minutes ago, swansont said:

You described an inelastic scattering interaction, which implies an absorption into a real state, and re-emission from that state. That's not what others are detailing.

I described what I believe others had posted so that I could demonstrate what it was I am not understanding.

"Bouncing, absorbed and re-emitted", all of those things happen and will happen to some light which is traveling through a medium which is transparent to that light i.e. the medium is not perfectly transparent to any wavelength.

But there is some light which travels through the transparent medium, is not bounced around, absorbed and re-emitted, and yet is slowed. The OP's post is that bouncing, absorbing and re-emitting is not a mechanism that adequately explains why light is slowed in a medium. This is explained in the video they posted and supported by the one I found from Fermilab.

Surely light propagates through a medium at the same speed i.e. all photons will traverse the same distance in the same time, two photons entering the medium together will exit together?

14 hours ago, Strange said:

No one says that the reason that light is slower in a material is because it is "absorbed and re-emitted".

Are you sure? It looked to me that some of the earlier posts were saying exactly that hence my confusion. I cannot understand how a photon can travel in a straight line, enter a medium and bounce around or be absorbed and re-emitted in random directions and then leave the medium parallel to its original direction.

However a photon traveling in a straight line until it reaches a medium, changing direction and going in a straight line through the medium and then resuming a path parallel to its original path does make sense. Interacting with a medium is not the same as bouncing around etc..

14 hours ago, Strange said:

yes, because momentum is a vector quantity.

As above

14 hours ago, Strange said:

A small amount of light will be scattered because no material is perfectly transparent. But that is not relevant to the subject of the thread.

Of course

21 minutes ago, swansont said:

You have to be careful, here. "light" and "photons" are not synonymous with each other, and don't mix quantum and classical models.

The speed of light is smaller in a medium. The speed of photons is still c.

Not something I'd considered/knew. In one of the videos they say that any of the component waves could be c but the super position of waves would be less than c. Does that mean the speed of the photon is c but the speed of light is <c

I don't understand this.

21 minutes ago, Strange said:

Or maybe I can't.

Or maybe I don't want to. Because it is a video and therefore a truly terrible way of communicating information. What next, interpretive dance?

Or maybe I watch it and then say, "no you are both wrong, what they actually say is that the photons get eaten by dragons".

If you can't find a proper source to support what you claim, then I am not going to take your claims seriously.

And that would be a strawman argument.

And you are under no obligation to watch it, I thought it would help in understanding the OP's reasoning.

The link I posted, as I stated, is By Dr Don Lincoln from Fermilab. This is verifiable by going to the Fermilab website which is what I did. So I think watching a video from an expert in his field from a world renowned establishment at the forefront of scientific thinking is a reasonable source for a discussion on a forum.

I don't believe I provided a strawman argument.

If you put a pencil in a glass of water it appears to be broken due to the refraction of light in/by water, the direction light that leaves the glass is parallel to the path it would have taken if the glass was not there. Their explanation was that if light bounced between atoms or was re-emitted you would not see a clear image of the pencil in the water, the light would be scattered and the image defuse.

This makes sense to me but if it is wrong perhaps you could explain how light can leave the glass parallel to its original path and still showing a clear image of the pencil

14 minutes ago, MigL said:

There is a cross-section for the interaction which depends on wavelength and atomic/molecular make-up ( for the purpose of this discussion ).

Otherwise any material could be used for fiber optic cable.
 

 

No memory.
But they do have momentum; and that is  required to be conserved.

I understand that cheese would not make a good fiber optic cable. If glass is transparent to red light and red light is slower in glass than in vacuo then it cannot be slower because it is bouncing around otherwise it would be defuse would it not? it would be like cheese.

Does conserving momentum equate to conserving direction? If a photon can bounce around in any direction when within the medium how does it acquire a very specific direction when it leaves the medium?

2 minutes ago, Strange said:

And that is why videos are such a terrible source. How can I know what they said in the video. But I do know what physics says, and it says that what you claim they said is wrong.

Fibre optics and prisms only work because the photons do interact with the atoms in the material.

 

You could watch the video and you would hear what they say, it may not be a great source but it is what the OP is referring to.

The link I posted is a video from Fermilab with Dr Don Lincoln who is easily found on the Fermilab website so there is some pedigree.

I didn't say photons do not interact with atoms, the super position of EM oscillations is after all interaction, I said they don't bounce around and are not absorbed and re-emitted (to clarify, some wave lengths are and some are not, depending on the medium). As far as I'm aware photons do not have a memory and so could not resume a path parallel to their original path.

With fiber optics and prisms I'm not referring to total internal reflection at the boundary, I'm referring to the propagation of light through the medium before it gets to the boundary. If light bounced or was re-emitted it would go in all directions.

18 minutes ago, Country Boy said:

Did you listen carefully to this?  The first person clearly say "light appears to slow down" while the other two  are referring to the average speed of light through the substance.  They are all saying the same thing everyone here is saying:  Light moves from one atom to another at speed c but takes some time interacting with each atom or molecule so that the average speed through the substance is lower than c. 

He literally said, "I want to prove to you that light really does slow down" (01:12) and he did not mention the average speed of light through the substance.

light does not bounce around between atoms nor is it absorbed and re-emitted otherwise fiber optics and prisms would not work. Let's remember the speed of light is c in vacuo

He gave 3 explanations

1. Light is a wave and therefore oscillates, there are EM oscillations of the atoms in the medium, the super position of these two waves propagates through the medium at less than c

2. light travels at the average speed of all possible paths through the medium (Young's' slits was used as an example)

3. Light ceases to be a photon and becomes a Polariton

On 2/11/2020 at 4:27 PM, timharvey027 said:

**removed link to video as you can scroll up if you want to watch it**

Prof Merrifield and Moriaty say it does, confused now.

I saw this just a few days ago which gives a similar explanation to the video you posted but with a little more detail.  06:15 for the explanation to start

https://www.youtube.com/watch?v=CUjt36SD3h8

12 hours ago, Gerrard said:

Still I think it is a project for general education. According to a poll, 53% of Americans believe that there was some sort of a conspiracy. That's pretty significant and may be a gateway conspiracy for other hard conspiracy beliefs. 

In any given population an IQ of 100 is defined as the average and marks the 50th percentile. This means that in any given population 50% are below average intelligence! Also I don't think 53% is statistically significant where you have a 50/50 choice i.e. it was a conspiracy/it wasn't a conspiracy.

Building a model that replicates the collapse of the buildings is a great hobby and will offer great rewards but the rewards will be educational not monetary.

1 hour ago, swansont said:

Part of that is that you shouldn't be asking me independent questions. That's thread hijacking.

My apologies

33 minutes ago, swansont said:

My previous answer was to the claim that it is always advantageous to travel near a massive object, which is patently false. As I had said, a photon going to a distant planet in the opposite direction doesn't gain an advantage by detouring around the sun.

 

The only way for that scenario to happen with simultaneously-emitted photons is if one goes through some medium to slow it down, or you bounce it off a mirror, but the photons will be taking different paths. So then you aren't comparing apples to apples. 

You could do it with and without the massive object at two different times, but they still won't travel the same path.

If the photons don't travel the same path, why is there an expectation that the travel time would be the same?

There is no expectation, there is a question. Your reply is one of pedantry and evasiveness! No offense, it may suggest I'm asking an invalid question! I'll try this.

If you had a glass sphere where the refractive index was greatest at the center and got progressively less as you moved out from the center following a 1/r^2 rule would the light follow a path similar to if it were passing a massive object through its gravitational field?

Is it a meaningless comparison, is it a reasonable visualisation like a heavy ball on a rubber sheet or can you consider the progressively changing refractive index in the same way you consider the progressively changing time dilation in a gravitational field?

7 minutes ago, swansont said:

That's a separate question from the one I was answering, but the path around the massive object will also be length contracted. Locally, an observer anywhere on that path will measure the light to be going at c.

 

 

 

So what I was thinking about is the question that came up earlier: if a photon traveling from one medium to another is refracted such that it follows the path of shortest duration between A and B (A is in one medium and B in the other) then if it was going through many layers of progressively increasing then decreasing refractive index would the path it follows be analogous to a photon traveling past a massive object?

I think that's the question you answered in the last two lines of your comment, I'm just not sure I understood your answer. That led me on to another question which is the one I asked.

In that question, yes "Locally, an observer anywhere on that path will measure the light to be going at c", I understand that. The question is, from B's POV one photon will arrive after the other because it has traveled farther, but from the photon's POV do they both consider they have traveled the same distance in the same time but one still arrives after the other? Being that they were both emitted together.

On 1/24/2020 at 3:33 PM, swansont said:

Starlight on a particular path — that which ended up at the telescope — followed that path. Light heading to Jupiter would not have traveled a shorter path by passing near the sun.

But the question here is : shorter than what? There's only one path to get from point A to point B that follows the laws of nature.

It sounds like you are trying to apply the principle of least time (Fermat's principle). That the path taken by light will be the one that has the smallest travel time, but that's not physically the shortest path in situations like materials with different indices of refraction. 

On 1/24/2020 at 3:42 PM, Mordred said:

I would suggest you look into the principle of least action and how it applies to the geodesics equation. I would also suggest you look at the Principle of equivalence.

mi=mg  

If two photons are traveling from A to B, one photon's path is uninterrupted whilst the other follows a curved path around a massive object the straight line photon will arrive at B first as it travels the shorter distance. The curved line photon will have traveled farther but will experience time dilation due the the gravitational effects of the massive object so will both photons have the same proper time even though one arrives after the other?

Something doesn't quite seem right with that???

For anyone who says 'do the math(s)' I am trying to spend 20 mins per day learning, I have finished multiplying pairs of brackets and am now on factorising. Gives you some idea where I'm at.

Would socks make a better analogy?

You have one pair of white socks and one pair of black socks.

if you lose one white sock you instantaneously lose one black sock.

But it isn't called the two clocks paradox or the who's the younger of two people paradox it is called the twins paradox and the fact they are twins has important implications, it implies:

1) they are in close proximity to each other

2) whilst they are in close proximity they are at rest with respect to each other, or both at rest to the same inertial frame

3) whilst they are in close proximity and at rest their respective clocks start simultaneously

4) their clocks tick simultaneously from then on (ignoring insignificant differences)

5) they are simultaneously the same age

if one of those twins were then put on a spaceship and flown around the galaxy at great speed relative to the inertial frame and returned some considerable time later to be with their twin they would once again be in close proximity, be at rest, their clocks would tick simultaneously but one will have ticked less than the others they would simultaneously be different ages. the statement 'they were simultaneously the same age but are now simultaneously different ages' is true

If in a different scenario there is a rogue planet speeding through the galaxy, traveling at a constant speed in a straight line and is heading straight for Earth at 0.9c. It is also true the Earth is heading towards the rogue planet at a constant speed in a straight line and at 0.9c. So there are two inertial frames heading towards each other at 0.9c.

Is there any way we can conclude that an event which occurs in one inertial frame happens simultaneously with an event in the other inertial frame (with the speed and distance involved). Can the birth of a child on Earth be considered simultaneous with the birth of a child on the rogue planet. If the answer is no then the statement 'they were simultaneously the same age but are now simultaneously different ages' is false. They were never simultaneously the same age

If you can conclude that events that occur in two different inertial frames, separated by some vast distance and approaching each other at some great speed, are simultaneous you can agree that two children born are simultaneously the same age. However if they were to fly off to meet each other, accelerating at the same rate for the same time, or, at the instant the planets pass each other you capture a photo (data) of the two individuals they will both be the same age still so the statement 'they were simultaneously the same age but are now simultaneously different ages' is again false. They are not different ages.

So the OPS experiment will explain time dilation and the time dilation will be equivalent to the twins time dilation but in the OPS experiment the statement 'they were simultaneously the same age but are now simultaneously different ages' is false.

and the statement 'they were simultaneously the same age but are now simultaneously different ages' can only be true where acceleration is involved.

so Einstein was right, if he were alive today I'm sure he'd be pleased to know that... (I mock myself)

9 hours ago, Markus Hanke said:

SR is well capable of handling accelerated frames as well; it’s just that the relationships between such frames are more complicated than simple Lorentz transforms. Where SR breaks down is when gravity is involved, i.e. when the region of spacetime in question is not flat.

All relativistic effects are relationships between frames; you would never observe any such effects, if you looked only at a single inertial frame.

https://www.einstein-online.info/en/spotlight/twins/

In the link above it seems to me that they are asserting the twin paradox (previously I stated SR) is the observable results of events within an inertial frame. For twins to be twins they must have been at rest relative to each other, or more formally both at rest relative to the same inertial frame of reference (IFOR), at some point i.e. the moment before they were born. Then within this IFOR one twin will accelerate, travel at speed, turn around and come back whilst the other one remains stationary.

So if the OP is suggesting that all clocks are synchronised whilst at rest relative to the same IFOR, are then moved to locations where they have the relative velocity and distance as set out in the OP and obey the timings and measurements as set out then is the OP, in part, right? However this is just a more complex twins paradox.

I am struggling with this though: if clocks which originated from outside the IFOR matched their velocity and position with the synchronised clocks they should give the same result, but this is not consistent with any explanation of SR I can find, to wit, the link above.

My understanding of SR (limited though it may be) is that it relies on strict application of rules. I believe SR only makes sense to an inertial observer, one who can be considered at rest and about which measurements are made/calculated.

In the experiment as stated by OP are we to assume that these are naturally occurring clocks and have been traveling in straight lines at constant speeds since the beginning of time and come together for the experiment. The unlikeliness of such an event is irrelevant, what matters is that none of the three clocks in the experiment can be considered inertial (or all three of them are in their own right)

or

Are they manufactured clocks which started off from inertial frames and have accelerated towards another inertial frame

or

Did all three clocks start of at rest relative to the same inertial frame in which case it is just the twins paradox

I think SR only makes sense if there is a single inertial frame of reference, is this not the case?

The three clocks in this scenario can only be synchronised whilst they are all at rest relative to the same inertial frame, anything else is meaningless. From this point on it's just a more complicated version of the "Twins Paradox"

On 1/16/2020 at 5:35 AM, Markus Hanke said:

...This is again one of those cases when I would simply sit down and employ the mathematical machinery, rather than trying to figure out the situation by intuition based on local laws.

I don't disagree but not everyone has the ability to do that.

So if a photon is emitted as blue light and received as red light is it the case that it still has the same total energy but it's energy is delivered over a longer period of time?

or is a photon all or nothing in which case it has less total energy?

Edit: I am thinking about expansion of space and not movement through it. I am trying to change my thinking not yours

Two assumptions followed by a question

1) Red shift of distant galaxies is determined by measuring the shift in absorption lines in a spectrum of light, however, it is not just the lines that shift but the entire spectrum.

2) Higher frequency light has more energy than lower frequency light.

Q. If light is emitted with more energy than when it is received where does that energy go?

On 9/1/2019 at 8:48 AM, md65536 said:

The twin paradox doesn't require an inertial twin. Suppose two twins left Earth at the same time and returned at the same time, each traveling a different but constant speed relative to Earth. Whom does your intuition say traveled a longer distance, the twin who ages more, or less?

Don't read the following puzzle if you want to think about it first.

  Reveal hidden contents

Two twins leave Earth at the same time and return at the same time, each traveling at a respective constant speed relative to Earth. Each measures the distance she traveled, and the time it takes. They find that one aged twice as much as the other, and they traveled the same distance. What were their speeds?

 

 

Bonus question: What speed should a twin go to maximize the distance it travels, for such a round trip?

 

On 9/4/2019 at 7:42 PM, md65536 said:

However, no one has yet taken a stab at the puzzle, by calculating the speeds of the two twins or clocks, given that they both measured (in their respective frames) having traveled the same distance relative to Earth, and that one aged twice as much as the other over the trip.

So they both left at the same time, traveled the same distance at different speeds but both returned at the same time?

What am I missing?

In a frame of reference described by x and y co-ordinates is it reasonable to describe a diagonal motion (what axis is this on?). Does this 'diagonal' motion not have x and y components of speed and therefore will appear to have contraction in both x and y directions?

 

 

... More than that, we can see galaxies that are receding at more than c!

 

 

I did not know that

I think a lack of clarity in the original question has led to conflicting answers here.

If the distance between our target galaxies is comparatively small and they are each moving through space with respect to A at 0.6c then the relative velocity between B and C will necessarily be less than c and they will be able to see each other. At relativistic speeds spacetime is distorted.

If however the distance between all galaxies is vast and their apparent speed is due to the expansion of space between them then they will not be able to see each other and their relative speed is meaningless. Any distortion in spacetime due to their speed through space is voided by the expansion of spacetime between them.

That's my thoughts

How long does it take for an electron to jump an energy level? Does time exist in a singularity? isn't physics full of t=0?

Have I not understood the question?