Light speed is constant?

Science and Technology
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What would it look like (in our telescopes) if the speed of light wasn’t constant? Wouldn’t it be the same if light slowed down over time? In other words if the red shift is due to light slowing down more the longer it travels.

To me, it seems like that would be a simpler answer to the red shift being greater the more distant a star is than the idea that the universe is expanding at an ever increasing rate.

The notion of a constant speed of light implies perpetual motion, something that is not supposed to be possible. A universe expanding at an ever increasing rate would seem to require an infinite amount of energy to do that much work.

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It isn’t. When it passes through some mediums, such as water, it slows down considerably. In the case of diamond, its speed is cut by over 50 per cent. But according to Einstein’s Special Theory of Relativity, the speed of light in the vaccum of empty space is said to be the same for all observers, at just short of 300,000km/s.

… Specifically, it’s the speed at which electromagnetic waves travel through the vacuum of space – and its value can be predicted by equations unifying our understanding of electricity and magnetism, as discovered over 150 years ago by the Scottish physicist and mathematician James Clerk Maxwell.

https://www.sciencefocus.com/science/why-is-the-speed-of-light-constant/


Or if you want to dig deeper check out this one,

Light travels at around 300,000 km per second. Why not faster? Why not slower? A new theory inches us closer to an answer.

By Sidney Perkowitz, emeritus professor of physics at Emory University.

https://aeon.co/essays/why-is-the-speed-of-light-the-speed-of-light


Then again, there are some rumblings that it has changed over time. But I’ll hand over the keys to Google to you and you can take it from here. :wink:

 

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Red/blue shift is due to the frequency of light changing and actually it is the constant nature of the speed of light which makes red/blue shift happen.

Say you are traveling on a train at 1/2 the speed of light and you shine a flashlight toward the front of the train. Common sense would dictate that light would travel at 1 1/2 times the speed of light, the same thing which would happen if you threw a baseball in that direction, increasing its speed. But because the speed of light is constant it still moves at the speed of light, the frequency of the beam just becomes compressed, shifting toward the blue spectrum. If you were to walk to the other side of the train car and shine the light the other direction it would not go that direction at 1/2 the speed of light, instead the frequency would be stretched toward the red spectrum. It is because light travels at a constant speed that this frequency changes, causing the color shift. Because it cannot change speed, the frequency is changed instead.

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If light was represented as an arrow travelling through the air, I suppose the blue would represent the point of the arrow whilst the red the other end.

The consistency of all colours would represent white providing the arrow was squashed into a dot. If however light travelled faster then I suppose it would stretch the arrow and the red would lag causing the blue to supersede. The argument of less dense into more dense gives us our rainbow effect. (I am lost)

Moving on…

Energy changes from one state to another and I think it is impossible to surmise where the energy comes from in an ever expanding universe unless we can see behind it?

We are just ants trying to work out the sugar bowl.

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The first part of what you posted is not really accurate, but you are really close. Instead of imagining an arrow going through space imagine really light spring which can be compressed or stretched easily. When the spring is just sitting there, not moving (meaning the source of the light and the light detector are moving at exactly the same speed and in exactly the same direction) the spring is at its natural length. If you grab one end of the spring and start running with it, pulling the spring along with you, the spring gets stretched out. If, instead, you push the spring from one end toward the other the spring gets compressed. This represents the wavelength of the light, which dictates its color. If the spring is compressed, energy has been added, the wavelength is shorter and the light shifts to blue. If you take energy away the spring gets stretched, the wavelength gets longer and the light shifts to red.

It is important to note that there is no such thing as a “white” photon. Photons come in all of the colors of the rainbow, which does not include white or black. When you are seeing white light you aren’t seeing white photons, the receptor cells in your eye are being struck by many, many photons of all different colors simultaneously. One interesting thing about light is that as it travels through space it doesn’t interact with other light. A red beam and a blue beam of light can pass right through each other and will not give you two purple beams. But when the photons strike matter they are absorbed. They may be remitted or converted into some other type of energy, but that’s not the point. The point is that when they interact with the matter, then they can change each other. So if you shine a red beam and a blue beam onto a piece of white paper in the same place you do get a purple dot. And that is what is happening in your eye. All those photons of all those colors are all striking the receptor and virtually the same time and they change each other in the collision with matter, allowing you to see billions of individual colors as one white light.

That question about energy is a little off too. It’s not “where the energy comes from”, it’s “where the energy came from”. The “stuff” that is in our universe now is exactly the same stuff that was in it the moment after the big bang. Back then it was all energy (and perhaps space, and perhaps time. Nobody is really certain what this “stuff” makes up, exactly), but as space expanded it began to cool (that’s not really accurate either. It had exactly the same amount of thermal energy, it was just spread out over more “space”, making it cooler in any given place even though it was exactly the same amount of energy). As it cooled then matter could begin to form. Before that any matter which may have formed was immediately annihilated back into energy by the extreme temperature. Matter and energy are interchangeable. The energy became the matter. This interchangeability is what allows matter to become energy in the center of the Sun.

But no, there is no way to know where it “came from”. It possibly always existed, it possibly began to exist because of a collision between two 11 dimensional membranes, it possibly was poofed into existence by some powerful being. Trying to know that is like trying to know what the air smelled like a thousand years before you were born. You can make some educated guesses based on what you know, but you’re still just guessing.

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Energy changes from one state to another
Energy is another "thing", like time, that we like to talk about but which isn't really there. What we call energy is the measure of the potential to do work. Work is the displacement of an object. The objects we are able to observe are fermions, things which obey the Pauli exclusion principle. So, what it comes down to is that energy is a measure of the motion of objects, not some sort of thing separate from those objects.
Red/blue shift is due to the frequency of light changing and actually it is the constant nature of the speed of light which makes red/blue shift happen.
The frequency of light doesn't change, unless the speed changes, and that was the point of my original post. The apparent frequency may change but that is due to the difference in velocity between the observer and the light source.
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Energy is another “thing”, like time, that we like to talk about but which isn’t really there. What we call energy is the measure of the potential to do work. Work is the displacement of an object. The objects we are able to observe are fermions, things which obey the Pauli exclusion principle. So, what it comes down to is that energy is a measure of the motion of objects, not some sort of thing separate from those objects.
"Work" may include raising the temperature of a given volume and density of material a certain amount. Or it may be converting the energy into some other form, such as from electricity into light. Work is not necessarily motion. Although that does touch on one interesting thought I had a few years ago. When you get to the very basest of levels for energy there are really only two types of energy; motion and electromagnetic. All energy is either an electromagnetic field or matter in motion, though some energy is a little of both (such as light).
The frequency of light doesn’t change, unless the speed changes, and that was the point of my original post. The apparent frequency may change but that is due to the difference in velocity between the observer and the light source.
The speed doesn't change at all ever. It takes light of any frequency the same amount of time to get from point A to point B in a vacuum. The "speed" of the light never changes and, in fact, it's the relative speed of the source which is important to the frequency.

Imagine this. You have 2 points, point A and point B, separated by 1 light year. Right in the middle you have an object emitting light. If that object starts moving toward Point A and away from Point B then Point A will see blue shift and Point B will see red shift.

I do see what you’re saying about the “apparent frequency”, but it’s not something generally considered in physics any more than actual direction and speed through space is. It is absolutely impossible to know the actual frequency of light or the actual direction and velocity we are traveling through space. We can only get the relative readings, so it’s the only reading which is relevant.

But yes, the actual frequency of the light does change as the speed of the source changes. If you were to force space to stop expanding for a moment and map it out precisely so you could measure actual frequency instead of relative frequency then as the source moved faster in one direction the light going in that direction would actually change to a higher frequency while the light moving in the other direction would actually change to a lower frequency. Being unable to measure actual frequency does not mean actual frequency isn’t changed.

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When you get to the very basest of levels for energy there are really only two types of energy; motion and electromagnetic. All energy is either an electromagnetic field or matter in motion, though some energy is a little of both (such as light).
If you can bring yourself to accept the possibilities of some sort of aether theory then everything observed is all motion (mechanical displacement by and of objects - fermions - which obey the Pauli exclusion principle). A mechanical universe is simplest, it even comes with a mechanical explanation of gravity. All that is required is accepting that there is a smallest particle; a particle which is so small it is far beyond our ability to observe it with known technology.
actual direction and speed through space
This is what we call velocity. Apparent speed (and frequency) is a function of relative velocity.
the actual frequency of the light does change as the speed of the source changes.
If we fly over a calm lake stopping periodically to drop identical stones from a consistent height each stone will make an identical wave in the water. That wave will not change in response to how fast we move between drops or the frequency of our drops. The wave is a function of the energy transferred from the stone into the water. Same with moving about ringing a bell in the air at different points. Same with light; the aether is displaced by an electron changing orbit. The wave in the water, air or aether will not change once it is introduced into the medium.

One wave may not be observable. Multiple waves reaching an observer over time will be observed as a frequency. The observed frequency will depend on the relative motion between the source and the observer.

I think I do not do a good job of explaining how I see this. I think we must consider the position of the source when a specific wave is introduced and the position of the observer when that specific wave is received and then consider the multiple waves which will be introduced and received in turn. I find it easier to see when I look at it as a geometry problem.

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...aether theory...
There is no such thing as "aether theory". It was discarded long ago.
If we fly over a calm lake stopping periodically to drop identical stones from a consistent height each stone will make an identical wave in the water. That wave will not change in response to how fast we move between drops or the frequency of our drops. The wave is a function of the energy transferred from the stone into the water. Same with moving about ringing a bell in the air at different points. Same with light; the aether is displaced by an electron changing orbit. The wave in the water, air or aether will not change once it is introduced into the medium.
Not true. As you change speed you are changing the energy imparted on the stone. And again, there is no "aether".

Another, simpler way of looking at the change in frequency of the light is to look at the change in frequency of sound as a train goes by. As the train approaches you the frequency is increased. As it speeds away the frequency is decreased. The actual frequency of the sound IS affected by the motion. The actual frequency change can be calculated if you know the base frequency, the speed of the train and the angle of the omnidirectional wave you wish to calculate the frequency change for. But the frequency can only be measured relativistically.

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As you change speed you are changing the energy imparted on the stone.
You seem to have missed the part about stopping to drop each stone.

Applying the notion of increased energy with increased speed to light, you are accepting that the speed of light is not constant. We accept that light doesn’t acquire or lose energy due to the motion of the source. As I posted, “The wave in the water, air or aether will not change once it is introduced into the medium.” Maybe you missed the part “once it is introduced into the medium”. This is true for sound too. Once the wave leaves the source, there is no mechanism to impart additional energy into it.

We must consider that each wave, each “ping”, each energy transfer is a single disturbance, not a series of disturbances. Thus there is no frequency associated with a single wave; frequency requires a series of waves. A wave is a single disturbance, a change from an initial state to a higher energy state and then back to the initial state. In quantitative terms this is a single event, not a process. This event occurs at a specific point in a medium (space) and the wave propagates away from that point at a specific speed. I accept that the speed of the wave through the medium is dependent upon the nature of the medium. I accept that the fact that a specific medium will propagate a wave at all must be dependent on the medium’s response to the motion of a particular object in that medium.

The actual frequency of a series of waves is the rate at which the source emits the individual waves. It is independent of the velocity of the source. As I posted, “The observed frequency will depend on the relative motion between the source and the observer.”

there is no “aether"
There is a medium (what we call space) through which light is transmitted as a wave. I accept that what we call a "photon" is the smallest amount of energy we can detect as a series of light waves impacts a body, not some particle flying through space. I have a bit of fun calling the medium of space the "aether".
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You seem to have missed the part about stopping to drop each stone.
I did, yes.
Applying the notion of increased energy with increased speed to light, you are accepting that the speed of light is not constant
What? No! And this isn't "me", this is physics as we know them. I am not the one claiming that light speed is constant and that its energy level is increased with increased frequency, all of physics is. And, I would point out, this has been proven as much as anything can be. This is.
We accept that light doesn’t acquire or lose energy due to the motion of the source.
Absolutely false. Nobody accepts that. Just the opposite is true. If you shine a flashlight directly forward as you move forward at half the speed of light the light coming out of the flashlight does not travel at 1 1/2 times the speed of light, it travels at the speed of light. But you must account for the energy you are adding to the light. You cannot create nor destroy energy, so that motion energy doesn't just disappear. It changes the light's frequency, putting the light at a higher energy level.
Once the wave leaves the source, there is no mechanism to impart additional energy into it.
That's true once it leaves the source. But the motion of the source imparts energy as it leaves the source.
We must consider that each wave, each “ping”, each energy transfer is a single disturbance, not a series of disturbances. Thus there is no frequency associated with a single wave; frequency requires a series of waves.
I think I see where you're going wrong here. Based on what you're saying here you're looking at a wave in water and a wave in physics being the same. What you're saying here is true of a single wave in water, but it is not true of a wave in physics. In physics a wave is one entire progression from median to upper peak to median to lower peak and finally back to median. (You can actually measure from any points that included all of that, but for simplicity it's usually shown like that and that's how we'll discuss it, again, for simplicity.) A wave in water is only half what a wave in physics is, the upper peak. There is a corresponding lower peak behind the wave, but it's not an equal height from the median (undisturbed surface of the water) because matter and energy bear little behavioral similarities. In physics the upper and lower peaks of a naturally occurring wave are equidistant from the median. (We can fudge that with electrical waves as much as we want, but it takes some serious interference on our part.)

Because a wave in physics is at least one entire progression every wave in physics has a frequency, which is calculated from that wave’s “wavelength”. The wavelength is the measurement of exactly one entire progression. It is the physical length of one iteration of that wave. From that wavelength we can calculate the frequency, and we can do that because we know the speed it is traveling. The formula to calculate frequency from wavelength actually uses the speed of light in the calculation.

Now this is important, every single photon has its own frequency. A photon is nothing like a pebble and a pond. That’s where your analogy went so wrong. The photon has a wavelength and, thus, a frequency as it travels. The photon travels as both a particle and a wave. It is, itself, the wave. And it’s nothing like a wave traveling through the medium of water. Space only acts as a medium in aether theory, which is garbage. You need to get aether theory out of your head altogether. Everything about it needs to go. A theory has to be really bad to be tossed out entirely instead of instead being modified to fit new understanding.

But all of that is irrelevant. We’re arguing facts here. The speed of light IS constant. This has been measured and proved and re-proved. This is not up for debate. This is not questioned. This just IS and will remain so until some observation says otherwise. You’re not going to change that with any theory or proposition or argument. The speed of light is constant, the end…until you can produce an experiment or some other observation which says otherwise. This is as solid and grounded a scientific fact as it gets. I cannot stress enough how wrong you are if you think you have any thought whatsoever capable of challenging this. You don’t. This is absolute, solid, known, undeniable, unquestionable physics until you can show that it’s not with observational data. You’re sure as hell not going to change that by digging through the trash bin of physics to try to revive aether theory.

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good summary -

@widdershins - But all of that is irrelevant. We’re arguing facts here. The speed of light IS constant. This has been measured and proved and re-proved. This is not up for debate. This is not questioned. This just IS and will remain so until some observation says otherwise. You’re not going to change that with any theory or proposition or argument. The speed of light is constant, the end…until you can produce an experiment or some other observation which says otherwise. This is as solid and grounded a scientific fact as it gets. I cannot stress enough how wrong you are if you think you have any thought whatsoever capable of challenging this. You don’t. This is absolute, solid, known, undeniable, unquestionable physics until you can show that it’s not with observational data. You’re sure as hell not going to change that by digging through the trash bin of physics to try to revive aether theory.
Seems to me it applies to "Physicalism" just as well -

Physicalism is to my understanding is an acceptance that the physical reality we are aware of is the product of atoms, energy and the rules of nature that they’ve followed since forever, which produced this planet where geology and biology combined to create and nurture life, through all sorts of amazing ups and down, with us being the current big deal, but knowing full well, it won’t last.

The reason I’m making a point of bringing it up is because I’m recently discovering just how freaken many question fundamental reality and even we as biological creatures, kin to all other creatures upon this planet. Kin to the pageant of Earth’s evolution.

When I started Hoffman’s Case Against Reality, I thought he was just some random kook. Turns out there’s a huge community of willfully self-delusionals, they call it dreaming, challenging, provoking, rejecting all that is old and tedious. All because they want to escape the mundane physical reality we are embedded within, in favor of fanciful dreams where one can soar like angels. Yes, I appreciate I’m including amazingly smart and accomplished people within that sweep of my net, so be it.

When one loses the appreciation for the distinction between one’s own thoughts and actual physical reality - something is seriously wrong.

What am I talking about here? All that “Time is Doomed” garbage - mathematical formulas, theorems within computer models, in idealized universes - an industry built on challenging fundamental physical reality. The stuff of careers and talk circuits. :-\

 

Just like the climate science denial. All fed and driven my an audience that doesn’t want to think about thing, they want escapism, because real life is such a drag.

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The analogy of light acting as a water wave, or a sine wave, is incorrect. Better to visualize the light wave as a pulse similar to a pressure wave such as a sound wave. For a single wave the transmission media is disturbed from a neutral state to a displaced state and back to the neutral state. There is no frequency associated with a single wave.

A photon is the amount of light recognized by a detector as the wave impacts the detector and creates a disturbance in the detector. The wave is not recognized directly by the detector. The wave is taken to be the cause of the disturbance in the detector.

Visualize a light source which will emit a single wave. Let us set up a number of detectors around that source. How many of those detectors will recognize (by registering a photon) the light source? It will depend on the sensitivity of the detectors of course. Based on our acceptance that we can detect light from very distant stars, the distance the detector is from the source will not be a significant factor at less than millions or even billions of light years. Note that the number of photons recognized will be the number of detectors and not a function of the source.

As for our ability to prove that the speed of light is constant, forget it. We have no capacity for measuring the distance required for light to give up energy into the medium. The CMBR is interesting as an indication of this energy transfer without the need to postulate a big bang event. The apparent redshift from distant stars is another interesting observation that is laid off to the motion of the stars but it can also be explained equally well by light slowing down over great distances.

Physicalism is probably correct for the 5% or so of the universe that we can detect.

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That was way off. Light is even less like a pressure wave than it is like a wave on water, not more. You’re thinking of a “wave” in physical terms, being something which starts from a central point and spreads out in all directions. That is nothing like a wave in physics. It’s certainly nothing like an electromagnetic wave at higher frequencies.

A “single wave” of light is actually a single photon, which does not spread out from a source, but travels in a single, unchanging direction unless acted upon by an outside source. A photon is not like a radio signal or a compression wave, it’s like a bullet. It just goes in a straight line. And actually the wavelike properties of electromagnetic radiation are just like a sine wave, but in 3 dimensions instead of two. It’s a pulsation, where it grows and shrinks from zero to its maximum amplitude and back again.

The problem is that there’s nothing in nature which we can “see” which acts anything like a photon, so it’s difficult to conceptualize. It would be akin to a disk or sphere traveling through space, growing to a maximum size, shrinking to zero and repeating as it travels in a straight line. So if you set up detectors around a source which emits a “single wave” the number of detectors which would detect it would be “up to one”.

It has been proved that a photon is not just “the amount of light which can be detected”. It acts both as a wave and a particle. Photons can be absorbed and emitted by other particles. That’s how glass works. It’s not actually transparent. No photon can get “through” glass. The photon is absorbed by the glass and re-emitted countless times as it travels through the material until it has made it out the other side. What you see on the other side is not the same photons which went in, but it is the same energy. Most of it, anyway. No transfer of energy is perfect, so there is some loss. I think I remember reading somewhere years ago that about 8% was lost, but that seems really, really high to me. And you may have heard some physicist muse that it takes a million years for a photon to get from the center of the sun to be emitted, but then only 8 minutes to get to Earth. That’s because the photon is absorbed and emitted over and over again, which is why physicists specify “the speed of light in a vacuum”.

As for the claim on physicalism, that’s just made up nonsense. The number you chose, 5%, is purely fictional and there is no evidence ever to suggest that there are any mysteries in the universe which do not have a natural explanation.

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It has been proved that a photon is not just “the amount of light which can be detected”.
I think this is not correct. I do not see how we can "prove" what something is without detecting it. I believe we still adhere to the idea that we detect effect and assign cause.
It acts both as a wave and a particle.
Which I think says, in more precise language, we detect effects which we assign to (best explain as) the action expected of both a wave and a particle.