This is art.

[Telecaster]

There's a podcast about the history of Hollywood movie making called You Must Remember This. It's thematic, with multiple episodes devoted to each theme. The latest series of eps was "Bela and Boris," centered around the careers of Bela Lugosi and Boris Karloff. I've gotten in the habit of listening to it while setting up guitars, to the point that I'll put off adjusting a neck, doing a restring, etc. until a new episode shows up in the queue. And when the podcast is between series, like now, I feel downright awkward tweaking a guitar without being accompanied by Karina Longworth's voice. 

-Dave-

[Rob C]

There's a podcast about the history of Hollywood movie making called You Must Remember This. It's thematic, with multiple episodes devoted to each theme. The latest series of eps was "Bela and Boris," centered around the careers of Bela Lugosi and Boris Karloff. I've gotten in the habit of listening to it while setting up guitars, to the point that I'll put off adjusting a neck, doing a restring, etc. until a new episode shows up in the queue. And when the podcast is between series, like now, I feel downright awkward tweaking a guitar without being accompanied by Karina Longworth's voice. 

-Dave-

David, that's worthy of an entire thread! Unfortunately, being the time of year, I have to devote my morning to another bout of bookkeeping, where I have to judge whether there's enough cash in the local bank to handle the car insurance, the next set of Community Dues for where I live, and a host of other end-of-year payments that fall into place. Seems that no sooner have I done it for one year but it's time for the next. There is absolutely no doubt that the older one gets the faster time does move. I don't think it's relative - I think it is factually so. Quite how the different speeds mesh in this so-called reality we inhabit I know not; guess it's all part of the grand mystery of life. Which zone the driver of that Amtrak train was in, doing 130kph in a 50kph zone, I know not. Fortunately my zones affect mainly just myself.

My fiscal exercise reveals, yet again, how dumb has been Brexit and its direct, exchange rates effect upon my financial health; for any to imagine its impact impinges only upon those living abroad, then they must also assume their own life on their little island is totally self-contained, that there is no dependency upon foreign trade whatsover. I bet many think just that. Maybe over 50% thinks just that; the same 50% that imagines it is now going to be even more of a trading nation. Talk about confusing contradiction!

Rob

[Telecaster]

One of the fun things you can do with Special Relativity is perform thought experiments that highlight how weird the cosmos actually is. You and a friend are travelling towards each other on parallel train rails at the same very high speed. A significant percentage of light speed in fact. You're on a souped-up solar system-spanning section of Tokyo's Tōkaidō Shinkansen railway. As your trains get closer you can use super-duper telescopes to see each other. You look at your friend through your scope while waving and you see her or him looking back and also waving. But your friend seems to be waving in slow motion, as though underwater. She or he smiles at you and the smile also seems to happen in slow motion. In the language of physics you're travelling at a relativistic speed and the slow motion you're observing is known as time dilation. But your friend's waving is a blur of sped-up motion as are her or his other movements.

Now switch to your friend's perspective. She or he is looking through a scope as your trains get closer and seeing you wave and smile. Your waving and smiling in slow motion also appears to your friend as a blur of motion. Now how can this be? If you see your friend moving slower faster relative to you, shouldn't your friend see you moving faster slower relative to her or him? In this case, no. You and your friend are both travelling fast enough that from both your perspectives the rest of the observable universe has slowed down sped up. This effect was first tested experimentally with atomic clocks in the early 1970s and has been confirmed by all such experiments to date. Our GPS system needs to compensate for it in order to work properly.

-Dave-

[Edit: corrections after a quick chat with a friend who's accustomed to my neophyte mistakes. "Ummm…you're giving an example of time contraction to explain time dilation." The part about atomic clocks and GPS is true but not as relevant as I'd thought, thus now also crossed out. I'll shut up now.  ]

[32BT]

One of the fun things you can do with Special Relativity is perform thought experiments that highlight how weird the cosmos actually is. You and a friend are travelling towards each other on parallel train rails at the same very high speed. A significant percentage of light speed in fact. You're on a souped-up solar system-spanning section of Tokyo's Tōkaidō Shinkansen railway. As your trains get closer you can use super-duper telescopes to see each other. You look at your friend through your scope while waving and you see her or him looking back and also waving. But your friend seems to be waving in slow motion, as though underwater. She or he smiles at you and the smile also seems to happen in slow motion. In the language of physics you're travelling at a relativistic speed and the slow motion you're observing is known as time dilation.

Now switch to your friend's perspective. She or he is looking through a scope as your trains get closer and seeing you wave and smile. You're waving and smiling in slow motion. Now how can this be? If you see your friend moving slower relative to you, shouldn't your friend see you moving faster relative to her or him? In this case, no. You and your friend are both travelling fast enough that from both your perspectives the rest of the observable universe has slowed down. Time dilation was first tested experimentally with atomic clocks in the early 1970s and has been confirmed by all such experiments to date. Our GPS system needs to compensate for relativistic effects in order to work properly.

-Dave-

That's because the relativistic "effects" are merely a direct result of the math involved. We use the math to predict the effects, we came up with the math because we observed those effects. The math is build on the premiss of a fixed speed of light and everything else either goes to infinity or to zero to compensate for that premiss. Like for example "we need an infinite amount of energy to accelerate a small mass to nearly the speed of light".

The far more problematic issue with the thought experiments is the reference frame: the math helps to convert from the observer to the observed, but it implies a third reference frame within which you and the friend are travelling in known directions...

But here is an even more intriguing question for you:
if we consider the speed of light as fixed, then what is actually causing red shift to occur?

[Rob C]

I have absolutely no idea about the physics of it -  my wife would have enjoyed this concept, especially if chemistry could be brought into the equation (she loved maths too) but I can tell you this: the more I am exposed to such ideas the more convinced I become that we are indeed creatures of a creator power.

In my mind, life seems just too complex, too brilliantly designed throughout the different species, and beyond that into the rest of what surrounds us and makes up what we are aware of in existence ever to have been accident. Much closer to home, I think of the circuitous paths that led me and my better-half to meet and go on to create our own little dynasty ever to be able to think of it as chance. Chance would have stopped us ever getting together that way - others had the same conscious wishes regarding us but to no avail.  It's another way of saying that what will be will be, but the obverse of that is that what is not never can be. So yes, I believe in a grander design than my own. Call it God, call it whatever name is convenient for the time and place, but for me it's very real. Better yet, it brings comfort for the long run. I think this is but a staging post, a stop on the way.

Rob

[Rob C]

But here is an even more intriguing question for you:
if we consider the speed of light as fixed, then what is actually causing red shift to occur?

The Purkinje shift, but in polarised light, of course. Everybody knows that.

:-)

[32BT]

I have absolutely no idea about the physics of it -  my wife would have enjoyed this concept, especially if chemistry could be brought into the equation (she loved maths too) but I can tell you this: the more I am exposed to such ideas the more convinced I become that we are indeed creatures of a creator power.

In my mind, life seems just too complex, too brilliantly designed throughout the different species, and beyond that into the rest of what surrounds us and makes up what we are aware of in existence ever to have been accident. Much closer to home, I think of the circuitous paths that led me and my better-half to meet and go on to create our own little dynasty ever to be able to think of it as chance. Chance would have stopped us ever getting together that way - others had the same conscious wishes regarding us but to no avail.  It's another way of saying that what will be will be, but the obverse of that is that what is not never can be. So yes, I believe in a grander design than my own. Call it God, call it whatever name is convenient for the time and place, but for me it's very real. Better yet, it brings comfort for the long run. I think this is but a staging post, a stop on the way.

Rob

For me the presence of a higher something is evident in this; every once in a while, not too often fortunately, you pass by a complete stranger and look them in the eye, however briefly, and you know with absolute certainty throughout the core of your being that you already know that person, that you are connected. Sometimes there is acknowledgement, almost as if you both want to say "hey, good to see you too!" but you don't say that because it would be an extraordinarily awkward thing to say of course.

That's what I like about EVFs. You'll never run into that problem while taking pictures...

[Telecaster]

But here is an even more intriguing question for you:
if we consider the speed of light as fixed, then what is actually causing red shift to occur?

Light speed isn't really fixed. What we refer to as the "speed of light" is the maximum speed that anything can travel in space. Massless objects like photons can go faster than anything with mass. (As far as we know.) But light can and does travel slower when interfered with. It interacts with mass. In the lab it can be slowed to a crawl by sending it through a superfluid.

Red shifting is a result of lengthening wavelengths rather than reducing velocity, though the same interaction/interference may result in both. Temporarily in terms of velocity, less so in terms of wavelength.

-Dave-

Disclaimer: I know a handful of astrophysicists, one of 'em quite well. But I'm certainly not one myself.

[32BT]

Red shifting is a result of lengthening wavelengths rather than reducing velocity, though the same interaction/interference may result in both. Temporarily in terms of velocity, less so in terms of wavelength.

The duration of detection. An interesting concept if you think about it, since we are on a photography forum.

Does it take less time to detect a blue photon as opposed to a red photon?
Or is it the duration of detection that determines the color we assign to it?
Does a photon perhaps always hold the same amount of energy, just compressed into a shorter length of time?

Is the duration of creation relevant? If the source is moving away from us, does the duration of creation increase relative to us as observer?

And in case you're wondering, yes, those are relativistic thought experiments that keep me awake at night. Or the questions come up when I'm already awake. Don't know. I have a cause & effect issue clearly...

[Telecaster]

The far more problematic issue with the thought experiments is the reference frame: the math helps to convert from the observer to the observed, but it implies a third reference frame within which you and the friend are travelling in known directions...

Neglected to put this in earlier… In Special Relativity the idea of a fixed reference frame, a background against which everything else can be observed and measured, is tossed out. In its place you get a fixed parameter, the "speed of light," which is the same in all reference frames. It's this fixed speed limit that leads to the time dilation effect observed by the rail travellers. Different degrees of it will be observed depending on how fast the travellers are going relative to each other.

None of this may be fundamental, but in our macroscopic realm it's holding up so far.

-Dave-

[Telecaster]

Does it take less time to detect a blue photon as opposed to a red photon?
Or is it the duration of detection that determines the color we assign to it?
Does a photon perhaps always hold the same amount of energy, just compressed into a shorter length of time?

You can think of a single light wave as always containing the same total amount of energy, packed into a tiny length (gamma ray) or a long one (radio frequency) or something in between. I'd think shorter wavelengths would correlate with longer duration since they pack more punch. Radio photons are zipping through us continuously, unnoticed, while the same amount of gamma photons would turn us into pulp pretty quickly.

Don't quote me on any of this. 

-Dave-

[GrahamBy]

But your friend seems to be waving in slow motion, as though underwater.

Is this the right way around? travelling toward each other, there will be a blue doppler shift, so the waving (which is after all just a low frequency oscillator) will be sped up... no? A simple way of thinking of it is that she needs to fit in the same number of waves while approaching, but the early waves take longer to arrive and the whole waving performance is therefore squeezed into a smaller time window.

The time dilation effect would be seen if you were watching your friend zoom past you while you were on the platform, so that her velocity vector would be instantaneously orthogonal to the line of sight between you. You'd also see it (as a general relativistic effect) if she was zooming into a black hole... because you never actually get to see her go over the event horizon, her last actions while approaching it get stretched out over a very long time.

And yes, GPS uses both special AND general relativistic corrections: the first to allow for the speed of the satellites, the second for the earth's gravitation field being smaller at the altitude of the satellite.

[GrahamBy]

if we consider the speed of light as fixed, then what is actually causing red shift to occur?

It's *because* it is fixed. The number of wave crests coming past you is invariant, so to fix up the relationship between the rate at which they are being generated in one frame and seen in another, the frequency of passing them has to change.

[32BT]

It's *because* it is fixed. The number of wave crests coming past you is invariant, so to fix up the relationship between the rate at which they are being generated in one frame and seen in another, the frequency of passing them has to change.

But that suggests a longitudinal wave which probably isn't applicable in the first place, but even so: regardless of how fast the source is moving towards or away from you, the photons will move towards you with the speed of light. So, if the observer frame is a frame at rest, then how come they still perceive a shift?

Considering the known dimensions, it would be reasonable to assume that a photon represents a single ripple with a specific duration. If a source is moving away from us (or is under gravitational stress) the duration seems to increase for the observer and thus the light seems to shift to red.

In the classical model it may also be the case that the electron jump becomes larger on one side of an atom and shorter on the other. Electrons have mass so they will experience inertia relative to the acceleration meaning they no longer make perfect circles, but slight ovals.

Again, this is not something i should be thinking about considering i prefer to sleep well.

[Rob C]

This is getting more interesting by the minute, but sadly, it's all way above my cranium; better check out before I hit a red light too. However, I shall enjoy the spectacle of debate from the platform - or the railroad if there is no station with cafeteria available.

:-(

Rob

[GrahamBy]

But that suggests a longitudinal wave ... reasonable to assume that a photon represents a single ripple with a specific duration. If a source is moving away from us (or is under gravitational stress) the duration seems to increase for the observer ... electron jump becomes larger on one side of an atom and shorter on the other. Electrons have mass so they will experience inertia relative to the acceleration meaning they no longer make perfect circles, but slight ovals.

Oscar I'm sorry, but do you know what any of these words mean? It's really not possible to think clearly when you just have a stew of undefined words. You are mixing up quantum and relativisitic physics, mechanical and EM wave ideas...

[Rob C]

Oscar I'm sorry, but do you know what any of these words mean? It's really not possible to think clearly when you just have a stew of undefined words. You are mixing up quantum and relativisitic physics, mechanical and EM wave ideas...

Which explains the menopause, which I've experience at least twice in my life.

The first one had me wanting to sell our house to buy a boat and live in it, in the Mediterranean; the second had me selling off my twin 'blads, lenses etc. to go 6x7. In the first instance, my wife saved us; in the second, she claimed not to care about photography any more, and probably wished I'd forget about it too. She was right the first time, probably the second time as well, but she failed to insist.

Like I wrote before, she was into the sciences. I think I preferred to dabble in metaphysics of my own construction.

Rob

[Eric Myrvaagnes]

So far I think Rob C's posts have given me a better understanding of special relativity than anybody else's posts.   

[KLaban]

So far I think Rob C's posts have given me a better understanding of special relativity than anybody else's posts.   

You should hear him on quantum mechanics!

;-)

[Telecaster]

Is this the right way around? travelling toward each other, there will be a blue doppler shift, so the waving (which is after all just a low frequency oscillator) will be sped up... no?

Yep, I got it backwards. "Again," as my friend Kate noted when I ran it by her. 

-Dave-