Is the brightness of light invariant?

You are actually correct qualitatively. Frequency does indeed increase due to the Doppler effect and decrease due to time dilation. (For an observer moving towards the source)

However, the math is important because without the math you are unable to know which effect is stronger. You are assuming that they are equal when you state that it decreases back to 1 Hz. If you did the math, however, you would find that they are decidedly unequal, with the Doppler effect overpowering the time-dilation effect.

-Dale

 

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A few points I feel I’d like to make….

Firstly to Pete. Pete, why would I want to retire my Hobbyhorse when there are literally dozens of unanswered questions? I, like many others, feel that there is something very wrong with our understanding of mass, inertia, gravity and light – pretty much all of the fundamentals of the universe. Yes we can measure and predict the outcome of experiments to a high degree thanks to a few critical and fundamental assumptions we made a few decades ago and also thanks to some very nifty mathematical manipulation. But there are concepts which clearly don’t make sense and trying to understand them is highly challenging and something I strongly believe will result in a paradigm shift at some time in the future. It’s happened before and it could very easily happen again. Pete, I totally agree that we are never going to break the maths of the situation and that you will always be able to provide evidence to support relativity in the form of mathematical equations. But that isn’t the point here. The point is that us “amateurs” want to know the answers to some blindingly obvious and incorrect concepts, one of which I’ve brought up in this QQ’s thread. I’m very grateful for receiving the knowledge I get from this forum but I’m afraid that, like many others, just learning and performing the maths isn’t convincing enough for me.

Physics Monkey – Why does the wavelength of EM waves change when altering your speed relative to a beam of light?

I’d also like to make clear that the point I’m making regarding Doppler shifting, frequency and wavelength being representative of a clue towards light being variant can be disassociated from relativity in this instance. In other words, time dilation and length contraction are a minor effect in comparison with the classical effect. So can we concentrate on the simple concept of why when an observer observes a Doppler shift do we deduce the preposterous conclusion that the speed relative to the light beam hasn’t changed? Just exactly what HAS changed if it isn’t velocity?

The other question….When we measure frequency and wavelengths of slow moving waves we discover that the frequency changes but the wavelength remains unchanged, thus the relative speed of the wave to the observer is calculable and found to be variant. With EM waves, we find that the wavelength is inversely proportional to the frequency and thus the sol is found to be invariant. So my question is…Are there any other waves found to be travelling close to the sol but not quite as fast? And if so, what happens to the wavelength here?

 

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Dav I must admit I empathises with you. It certainly appears that no matter which aspect of SRT you attempt to understand intuitively or logically you always hit a wall and a call for mathematical evidence as proof.

For some reason it seems that SRT can not be properly explained in plain English verbally using normal logical and rational methods.

Possibly this is because no one on this board is an Abert Einstien or a Lorenze and can explain SRT thoroughly using only words that make sense. A verbal explaination is either too difficult or not possible in the short speak of internet forums.

To explain how SRT is derived from the ground up seems to be a very difficult ask.

I think your question is quite valid and logical and should be easilly answered with simple English. Obvously it isn't that simple.

 

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I think one of the clues to this riddle is that light does not have a relative velocity. It only has a speed of change that is the same as the rest of the universe.

Or to put it this way :
The wave changes position at the same rate that the universe moves through time or changes though time. Thus light has no velocity but only speed of change in position. So doppler effects are not indicative of lights speed and only the observers or what is observed speed.

So as the wave moves from point A to point B the universe has changed at the same rate. Thus light has a very unique attribute. It is a constant because the entire universe is changing with it at the same rate. not faster or slower.

This constant must be maintained and thus when an object is given velocity it's time and length must change to accomodate that extra velocity as nothing can go slower or faster than light. When an object reaches a Relative 'c' which of course is impossible it's full energy is realised and E=mc^2 becomes valid. The object is travelling at c^2 and is no longer mass but pure energy traveling at only 'c'. So as it goes faster it's time and length are altered to maintain the rate of change at 'c' So faster is in effect an illusion as really it's change rate remains constant as 'c'. THus always considered as at rest to itself. Dimensions collapse and what we end up with is light. Mass has made the transition to it's energy state.


My thoughts...anyway.

 

QQ,
If you want to understand relativity, you're going about it the wrong way. I think if you asked Einstein or Lorentz about it, they'd show you the maths.
If you want to understand relativity, why don't you pick up a text book that is written for the purpose of explaining it, and work through it?

 

dav,
You're not acknowledging when questions are answered. You keep going back to square one. Are you just not trying to learn? The impression I get is that you're riding a "modern physics is broken" hobbyhorse, and you really don't want to get off it. I think that you are afraid of discovering that modern physics isn't broken, so you're not willing to consider the possibility.

Perhaps I'm wrong. I hope I'm wrong. Meh.

Anyway, the point of the maths is far from a dumb "plug in numbers... get answer" sort of tool. The key to understanding is in understanding what the equations mean. And really, it's not hard to understand the maths...it's much easier than trying to understand things without understanding the maths. I don't even know if that's possible!

 

What's the difference between "velocity" and "speed of change in position"?

 

Pete, I WILL achnowledge when questions are answered but as yet they haven't been. Like I said, the rigor of mathematics is adequate enough to demonstrate and prove our ability to predict the outcome of our experiments. But it dos NOT answer the underlying difficulties that science faces when answering questions based on certain fundamentals. ie what is mass? what actually causes gravity? Why does light appear invariant? Why does the wavelength of EM waves change as the observer alters speed?

Anyway, I believe that maths is very powerful and something I deeply respect but it is only a tool afterall. The first stages in scientifically researching a subject is always the "idea" or the initial concept of some possibly currently considered outrageous notion. Only afterwards does the maths come into its own. I'm absolutely certain that mathematical solutions could be found to fit in with most observable situations and help predict the outcome of experiments once algebraic formulas have been derived. Einstein did it this way round, didn't he?

For instance, why was the idea of a dynamic and variable density aether dropped? It is perfectly feasible, from what I've read, to use this as a model without too much difficulty. It takes care of stellar aberation and the MM experiment amongst other things. I'm sure that we could find a mathematical model to support this idea.

This is why I belive that thought experiments are far more powerful than you might think. Einstein supported this idea and although I'm no Einstein, I too hold this belief.

 

DaleSpam,

I agree with you. I'm stating that it appears to me that the combined effects of time dilation AND length contraction should negate the Doppler effect.

Regardless, like dav57, I still can't understand how the frequency of an existing wave can change without the speed of the wave relative to the observer changing as well. Do you have an explanation for that?

 

Again, you are correct, time dilation and length contraction do negate the Doppler effect, just not completely. In other words, say you start with the 1Hz signal you were discussing previously and say that the observer is moving at .5c towards the source. Then the Doppler effect shifts it to 2Hz, but time dilation and length contraction bring it down to 1.73Hz, not all the way back to 1Hz.

I liked leopolds' analogy earlier in this thread (except for the fact that the posts actually are passing by at different speeds) and I have seen several other similar analogies elsewhere on this forum. I personally like the "throwing sticks onto a steadily-flowing river" analogy. They are more useful for understanding the Doppler effect for sound waves, but the basic idea behind the EM Doppler shift is the same as long as you consider a single frame.

Let's look at it in the observer's frame. The emitter is emitting radiation at a particular frequency which would have a particular wavelength if it were stationary. However, in the time between two successive wavecrests the emitter has moved, thereby changing the wavelength from the stationary value. These altered wavelengths hit the observer who therefore observes an altered frequency.

If you spend a minute thinking about the Doppler shift for a brief pulse it becomes obvious that the important velocities to consider are the velocity of the emitter at the time of emission relative to the velocity of the detector at the time of detection. After all, the velocity of the emitter and the velocity of the detector both at the time of detection are spatially separated so they cannot be causally connected. So even if a source has ceased to exist by the time of detection it certainly existed at the time of emission and so it can easily have a Doppler shift.

-Dale

 

So in doppler shift situation how does one measure the speed of light?

If doppler shift is caused by an altered rate of waves caused by a change in their relative speed to the observer how can the observer measure the speed of the waves as being the same as if doppler shift was not occuring?

 

In other words, If lght being emitted was 1 hertz light and is only changing due to doppler effects it is still 1 hertz light yes? But seen as another hertz. So the waves are still as they should be with out doppler effects which are an observer pheno and not a light pheno. Even with doppler effects the waves remain as 1 hertz.

Those waves for 1 hertz light are being recorded at a faster rate but are still just 1 hertz light waves. So how can the light be able to have it's speed recorded as 'c' if those 1 hertz light waves are being recorded at a faster rate. The lights speed is the speed of it's waves afterall is it not?

 

Dalespam, thanks for that. But I want to make it very clear that QQ, Prosoothus and myself have a full understanding of the Doppler shift.

It's why the frequency rises when you move faster towards an already emitted wave which is causing us the bother. And also why the wavelength of EM waves changes.

 

So Dav57, are you suggesting that the observation of doppler shift is actually evidence that the postulate that is the foundation of SRT is fatally flawed?

If this is so, I find it incredible that this simple understanding of doppler shift has passed so many a critical thinker, so incredible in fact that I must suggest that there must be a simple explanation that would clear up the validity of such evidence.

In other words I can't believe so easilly that so many astute scientists could make and miss such a fundamental error of rational.

 

dav57, you can add me to the group, also. I have been arguing against the 'constancy of the speed of light for ALL inertial observers' for a couple of years.

When physicists work the mathematics as they normally do, from the 'rest frame' of the observer, the changing velocity is always a product of the 'other' frame. If the 'other' object changes its velocity relative to the 'rest' observer, the light from the other 'moving' frame will be Doppler shifted from the moment of emission. Physicists do not want to give up their method of calculating from the 'rest frame' since doing so would negate the constancy of the speed of light for all inertial observers. That is the reason for the intense arguements regarding a 'preferred' frame of reference, or a so-called 'absolute' frame of reference. That is why you cannot 'move faster towards an already emitted light wave'. You are 'at rest' and the object that emitted the light wave 'moves faster', the Doppler shift caused by the velocity of the moving frame relative to your rest frame. You will sometimes see an explanation that the light wave is 'compressed' by the difference in relative velocity. If the wave is compressed, that means it was travelling faster than 'c' BEFORE it was compressed by the observer. Yes, I know I am in conflict with Special Theory and the Lorentz transforms.

 

Surely a simple gendanken could be made to show this problem clearly.

For example:

Two light sources 100 lys apart but co-moving at the same V.
Observer positioned at 50 lyrs and observes the same light frequency from both stars and as both starts are emitting at the exact same frequency he can conclude he is stationary betweeen these two lights sources.

Star--------------Observer---------------Star

As the observer moves towards one of the stars he should record a doppler shift regarding light recieved from both sources. One shifts to an increased frequency the other shifts to a decreased frequency.

At all times the light frequency hasn't changes however the recording of it has. The two sources are still emitting the same frequency as they were when the observer was stationary in between them.

Just to make it more certain there is an observer at each star recording the other stars emmissions as being steady and the same as the other star.

So how does the observer record a shift in frequency from both sources and yet maintain lights speed as the same as when he was stationary between the stars?

 

Of course as 2inq has suggested we could simply state that the co-moving stars are doing all the movement and the observer is stationary.

But what would happen if there was a star in the center and two observers were heading towards that central star at the same v.

Observer------->------Star------<---------Observer

The star is enmitting a uniform frequency which each observer records as shifted to the same amount. The star can not be considered to be going in both directions simultaneously can it?

 

Yeah, and how about this one…

Star A-----Observer-----------------------------------Star B
>Near light speed>

Star A and Star B are 100 ltyrs apart and stationary relative to one another.

Observer is very close to A and on his starting blocks

Star A emits a ray of light towards B which obviously takes 100 years

Star B emits ray of light also.

As the ray from Star A passes observer, observer quickly accelerates to near light speed (but not quite)

When Observer reaches middle he looks at both rays and views one as being massively red-shifted and the other as massively blue-shifted.

Another observer in the middle who has been stationary all of the time records some timings. He concludes that the ray from B to A took 100 years. He records the Ray from A to B as also taking 100 years. He noticed that the fast observer takes 101 years.

So how the hell can the fast moving observer possibly have been moving at c relative to both beams. It’s a nonsense.

 

You guys aren't even trying to learn, are you? Are you really happy in your ignorance? Come on, put some effort in! Don't make me do all the work for you!

 

Dav, on the surface it does seem to be nonsense but I have seen this successfully argued as not being the case....However I wonder about the star in the middle scenario and how that can be argued through.

When the star can only be considered stationary to both observers.