How does the right hand rocket provide the energy to move that fast?
Is the brightness of light invariant?
- Thread starter Quantum Quack
- Start date
And also how can the left hand rocket be stationary if it has expended energy to give it momentum.
It is up to you to show reason why we should accept that the rocket has no velocity even after expending energy.
How does the star get the energy to go from wow to go......what about inertia and so on.....come on Pete give me a reason to take your solution seriously.
It is up to you to show reason why we should accept that the rocket has no velocity even after expending energy.
How does the star get the energy to go from wow to go......what about inertia and so on.....come on Pete give me a reason to take your solution seriously.
Ok similar scenario, but this time both yellow LSMD's are winched with the use of cables towards the light source The T frame has a hypothetical massive planet scale inertia where as the LSMDs are ultra light [weighing less than an average motorcycle.]
Explain how the inertia of the T frame can be over come thus allowing one of the LSMD's to seriously consider himself at rest and able to pull the entire T frame and other LSMD towards it.
<img src=http://www.ozziesnaps.com/doppler3.gif>
The blue winching station pulls cables attached to the LSMD's via a central pivot pulley located under the light source.
The rigid T frame could be an analogy of an aether if you like.
Explain how the inertia of the T frame can be over come thus allowing one of the LSMD's to seriously consider himself at rest and able to pull the entire T frame and other LSMD towards it.
<img src=http://www.ozziesnaps.com/doppler3.gif>
The blue winching station pulls cables attached to the LSMD's via a central pivot pulley located under the light source.
The rigid T frame could be an analogy of an aether if you like.
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Pete said:
But at the beginning of the experiment all bodies were stationary when the star emitted the light. Nothing happened until the ROCKETS expended some energy and all bodies agreed that that it MUST be the rockets that changed their position in space, NOT the star.
We are going round in circles and I can see that relativity is clearly incorrect using the loophole you are using. But when using the loophole and allowing the source to become the reason for the Doppler shift regardless of who moves, I would be forced to agree 100% with relativity. Clearly, something is wrong and I remain unconvinced.
You know it is often the bain of SRT'ists frustration that persons don't bother to get educated about the math etc.
If any one can show me reason to allow that the inertia of a massive body can somehow physically be ignored then maybe I and others might consider that it is worth doing the serious study.
It seems to me that the approach to this simple question is to ignore the physical reality of inertia. Which I find most puzzling when I hold the repondents with such respect.
If any one can show me reason to allow that the inertia of a massive body can somehow physically be ignored then maybe I and others might consider that it is worth doing the serious study.
It seems to me that the approach to this simple question is to ignore the physical reality of inertia. Which I find most puzzling when I hold the repondents with such respect.
Dav it is freeware called Serif Draw plus 4. I got it free about 12 months ago. I am not sure if it is still available.
Hi dav,
It might help if you actually read the replies of the other posters. I already asked you once already why you would think it makes any sense to talk about classical (as in, non relativistic) light. Light isn't classical! Light is relativistic! Stop acting like light is sound wave. Please.
Also, the Doppler shift is determined by your speed relative to the source. How many times do Pete, Dalespam, and I have to tell you this before you get it? When you speed up or slow down, something has changed! Here it comes, so pay close attention. What has changed? Your velocity. Ok, relative to what? Relative to a certain inertial frame. Ok, what inertial frame? The instaneous rest frame of the source. Ok, what if the source is accelerating? Use the rest frame when the source emitted the light you see now. That is the full answer.
dav57 said:
It might help if you actually read the replies of the other posters. I already asked you once already why you would think it makes any sense to talk about classical (as in, non relativistic) light. Light isn't classical! Light is relativistic! Stop acting like light is sound wave. Please.
Also, the Doppler shift is determined by your speed relative to the source. How many times do Pete, Dalespam, and I have to tell you this before you get it? When you speed up or slow down, something has changed! Here it comes, so pay close attention. What has changed? Your velocity. Ok, relative to what? Relative to a certain inertial frame. Ok, what inertial frame? The instaneous rest frame of the source. Ok, what if the source is accelerating? Use the rest frame when the source emitted the light you see now. That is the full answer.
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Quantum Quack,
Please stop and think carefully about what you're saying. Since when do objects have absolute motion? If I am on the surface of the Earth and I start running, buildings are now moving with respect to me. They have a kinetic energy in my frame. So what! I've changed inertial frames. The motion of objects depends on what I refer that motion to. Since when has there ever been a principle of conservation of energy between reference frames. This is so obviously not true even in the most elementary applications of classical mechanics that I don't know how you could have ever got the notion in your head. So get it out of your head. When you accelerate towards a star, you haven't accelerated the star (a physically distinct process). You've simply changed your point of view to a frame where the star is moving. There are infinitely many such points of view where the star is moving in all different directions with differents speeds and different kinetic energies. This is no violation of energy conservation.
Also, I'll ask you the same question I asked dav57. Why the strange fear of mathematics? It's quite obvious that you aren't succeeding in reasoning with English words. Mathematics is a language built for precision.
Please stop and think carefully about what you're saying. Since when do objects have absolute motion? If I am on the surface of the Earth and I start running, buildings are now moving with respect to me. They have a kinetic energy in my frame. So what! I've changed inertial frames. The motion of objects depends on what I refer that motion to. Since when has there ever been a principle of conservation of energy between reference frames. This is so obviously not true even in the most elementary applications of classical mechanics that I don't know how you could have ever got the notion in your head. So get it out of your head. When you accelerate towards a star, you haven't accelerated the star (a physically distinct process). You've simply changed your point of view to a frame where the star is moving. There are infinitely many such points of view where the star is moving in all different directions with differents speeds and different kinetic energies. This is no violation of energy conservation.
Also, I'll ask you the same question I asked dav57. Why the strange fear of mathematics? It's quite obvious that you aren't succeeding in reasoning with English words. Mathematics is a language built for precision.
Physics Monkey said:
Yes, I know that PM.
Physics Monkey said:
No, it is not the full answer PM. I'm really sorry. Truly, I am. I can not accept that QQ's twin rocket scenario places the source as the moving object which ever way you look at it. All observers must conclude from the evidence that it is the rockets which are moving during the experiment. It is them who change their velocity, NOT the source. Please don't get angry with me. Surely you must see where we're coming from.
Anyway, what did you think about my reason for the "altering" wavelength in a previous post?
Hi dav,
I'm not angry with you, I'm just confused and saddened when it seems like a reasonable person is missing the obvious answer.
In QQ's rocket picture, the two rockets are moving toward the star from opposite sides. They are in motion relative to the source, and they experience a Doppler shift. When they switch from moving towards the star to moving away from the star, both rockets have changed their motion relative to the source and experience a different Doppler shift. What is your problem with the above explanation?
I'm not angry with you, I'm just confused and saddened when it seems like a reasonable person is missing the obvious answer.
In QQ's rocket picture, the two rockets are moving toward the star from opposite sides. They are in motion relative to the source, and they experience a Doppler shift. When they switch from moving towards the star to moving away from the star, both rockets have changed their motion relative to the source and experience a different Doppler shift. What is your problem with the above explanation?
Physics Monkey said:
Because as you said, the ROCKETS are the ones whe are moving and it is they who experience a Doppler shift. And this Doppler shift is due to the fact that the rockets have changed their speed relative to both the source and the beam they are actually viewing at the moment of measurement.
I must be really thick but the STAR and the BEAM of light haven't done anything. It is the rocket which has moved and being as the rocket experiences a faster rate of peaks of the wave then it is pretty reasonable to conclude that the rocket is moving faster relative to the beam.
And further more, I would expect to measure a shorter wavelength. I thought this up way before I knew anything about relativity. Then I find that relativity throws the reason for Doppler as being due to the movement of the source in all cases. And I can't seem to accept this when considering QQ's model.
I guess I'm the type of person who won't accept ANYTHING unless I can start from fundamentals and work my way through it from the outset. I can't get past this, what appears to be a, get-out clause.
dav57 said:
Come on, dav... you can do it.
Picutre this setup on a tabletop. The star is a light source bolted to the table, the rockets are two detectors on rails approaching the light source from either end.
The same logic still applies, right?
But hang on... do you think that the table is necessarily stationary? Will anything seem any different if our table is on a train, plane, ship, truck, or planet that happens to be moving?
What if while I'm doing this experiment, I glance out the window and see you drift past the window at a speed that exactly matches one of the "rockets"... but as it happens, you are standing on solid ground, and I'm the one drifting.
How can I tell whether I'm moving or not?
Then that's what you need to do.dav57 said:
Start with Galileo, and go from there. Your best bet is probably a textbook - that's what textbooks are for, after all!
Be warned - you will need to do some maths. I strongly suspect that you can gain an adequate understanding without being able to do some of the maths involved.
Physics Monkey, myself, and I'm sure other on the forum are willing to help you out... but one step at a time. I think this doppler effect discussion is wrong-tracked, because we're working with different models. You are implicitly assuming the existence of absolute space. We're not. If we can't surmount that hurdle, we'll never make progress.
Because in the point of view from which the rocket is now stationary, it was previously not stationary. It expended energy to change its momentum to zero.Quantum Quack said:
Point of view (just another expresion for reference frame) is all important, QQ.
Kinetic energy, momentum, velocity all depend not only on the object's state, but also on the point of view.
The left-hand rocket has definitely changed its momentum... but in one point of view, it has change from zero to some positive value, while from another point of view it has changed from some negative value to zero, while from another point of view it has changed from some large positive value to some small positive value, etc etc etc.
The star doesn't expend energy. Its state does not change. In all points of view, the star's momentum does not change. If it is moving in some point of view, it was always moving in that point of view.
So if what ever the result the doppler shift recorded shows the absoolute velocity of the light source. And no matter what happens the rocket doing the recording is at absolute rest.......So by using the rate of light waves we can deternmine the exact absolute velocity of a light source? If not...[ seeing as these absolutes are forbidden by SRT] what exactly is the relationship between ship and light source? Is it possible to determine anything about this relatioship using light waves?
How can a doppler shift be measured? What is the base lin ethat the shift is using to determine the amount of shift.
So a ship in another galaxy moving in a differrent direction would record a different doppler shift that a more local ship?
Thus the star is going in more than one direction at a time, as the light emmissions are invariant.
Pete, I just don't see how you can have it both ways.
If the frequency emitted by the star is only true in the stars rest frame then we should be able to determine the stars absolute velocity using the stars RF.
Now I know for sure that SRT forbids such a determination. So what does the emmissison rate of the star tell us? Absolutely nothing of value about it's velocity or direction. So dopller shift is totally usless....
Sorry for the above,, however
If I have a ship that is stationary regarding the star and still records a doppler shift what does that imply about our stars movement.
So a doppler effect can be recorded by a ship even though it is stationary with regards to the star?
Well that would make your statement about relative movement make sense I guess.
How can a doppler shift be measured? What is the base lin ethat the shift is using to determine the amount of shift.
So a ship in another galaxy moving in a differrent direction would record a different doppler shift that a more local ship?
Thus the star is going in more than one direction at a time, as the light emmissions are invariant.
Pete, I just don't see how you can have it both ways.
If the frequency emitted by the star is only true in the stars rest frame then we should be able to determine the stars absolute velocity using the stars RF.
Now I know for sure that SRT forbids such a determination. So what does the emmissison rate of the star tell us? Absolutely nothing of value about it's velocity or direction. So dopller shift is totally usless....
Sorry for the above,, however
If I have a ship that is stationary regarding the star and still records a doppler shift what does that imply about our stars movement.
So a doppler effect can be recorded by a ship even though it is stationary with regards to the star?
Well that would make your statement about relative movement make sense I guess.
In the point of view in which one of the LSMD's is stationary and the T-frame is moving, the T-frame was always moving. Before the winch was started, the LSMD in question was also moving in that point of view. Starting the winch changes the LSMD's motion from moving to stationary.QQ said:
Pete said:
Pete ultimately this all leads to the situation that a ship could actually be co-moving with a star and thus even though it is stationary with the star it should record a doppler shift.
So how would our ship interpret such a result knowing that it is stationary with the star?
EDIT - I initially included some lines at the start of this post that evidenced my frustration. I delete those lines, and apologise for including them in the first place. I'd really like to continue this discussion dispassionately and objectively.
Here's another way:
The doppler shift shows the velocity of the source (when the light was received) in the point of view in which the observer is stationary (when the light is received).
Do you get it? The doppler shift tells us something about the source's velocity from a particular point of view only.
The doppler shift shows the velocity of the source (when the light was emitted) relative to the observer when the light is received.Quantum Quack said:
Here's another way:
The doppler shift shows the velocity of the source (when the light was received) in the point of view in which the observer is stationary (when the light is received).
Do you get it? The doppler shift tells us something about the source's velocity from a particular point of view only.
The base line is the emitted frequency or wavelength in the source's point of view.
Yes, because that ship is stationary in a different point of view. It's position doesn't matter, only it's motion.
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