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| rhysboi1991 |
 Posted: Wed Feb 24, 2010 5:40 pm Post subject: the doppler effect energy problem |
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Joined: 26 Jan 2008
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Location: Cumbria, North West England
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hell a little problem, imagine a star very far away travelling very fast away from us and a photon is emitted from it in our direction, the photon will be red-shifted and according to the relationship E=hf if the frequency is decreased there is an energy loss. Where does this energy go?
and vice versa if it is moving towards us the frequency of light is increased therefore energy is gained where does this energy comes from?
please reply
thankyou  |
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| DrRocket |
| Posted: Wed Feb 24, 2010 5:55 pm Post subject: Re: the doppler effect energy problem |
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Forum Radioactive Isotope
Joined: 12 Aug 2008
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| rhysboi1991 wrote: |
hell a little problem, imagine a star very far away travelling very fast away from us and a photon is emitted from it in our direction, the photon will be red-shifted and according to the relationship E=hf if the frequency is decreased there is an energy loss. Where does this energy go?
and vice versa if it is moving towards us the frequency of light is increased therefore energy is gained where does this energy comes from?
please reply
thankyou |
En3ergy is dependent on the rest frame of the observer. In your example there is no energy gained or lost, so no problem at all. |
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| himnextdoor |
| Posted: Wed Feb 24, 2010 9:46 pm Post subject: |
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The thing is that the photon isn't red-shifted; only the portion of the light-wave that is travelling towards you is. The part of the wave that is moving away from you (which you can never see) is blue-shifted.
I think it is better to think of a photon as an event that causes an electo-magnetic wave in the same way that a stone dropped into a pool of water causes a ripple. A photon can be any event from an electron changing its energy state to nuclear collisions in the same way that a stone can be anything from a grain of sand to a boulder of rock. |
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| DrRocket |
| Posted: Wed Feb 24, 2010 10:03 pm Post subject: |
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| himnextdoor wrote: |
The thing is that the photon isn't red-shifted; only the portion of the light-wave that is travelling towards you is. The part of the wave that is moving away from you (which you can never see) is blue-shifted.
I think it is better to think of a photon as an event that causes an electo-magnetic wave in the same way that a stone dropped into a pool of water causes a ripple. A photon can be any event from an electron changing its energy state to nuclear collisions in the same way that a stone can be anything from a grain of sand to a boulder of rock. |
No. It is indeed the photon that is red-shifted. Electromagnetic waves are just a lot of photons. You cannot spit a photon into two parts.
You are thinking of photons in the wrong way. |
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| himnextdoor |
| Posted: Wed Feb 24, 2010 11:16 pm Post subject: |
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How big can a photon be?
Is it not the case that each photon-producing event causes an electro-magnetic wave to propogate through space?
One photon-producing event, one photon, one wave?
If a source of photons emitted one photon every second, how precisely would a photon detector need to be placed in order to count them? Wouldn't a detector placed at the side of it detect them also?
Sorry about all the question marks.
It seems unfeasible that every electro-magnetic source emits an infinite number of photons all the time. |
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| MagiMaster |
| Posted: Thu Feb 25, 2010 12:50 am Post subject: |
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| No, if one photon is produced, it will be produced with a direction, and a detector placed to the side will not detect it. (This is done regularly during testing of any number of QM effects.) |
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| Ghrasp |
| Posted: Thu Feb 25, 2010 4:36 am Post subject: |
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Suppose you have a installation as with the double split system. There is a screen with two slits and one photon goes thrue both slits at the same time. Suppose you,re looking through one of these slits as a window and someone else is looking through the other slit. In astronomy the screen can be replaced to two telescopes. So the one next to you can see the same photon.
With the screen and the two slits you can remove the screen with the slits. You'll see one lightspot on the other screen (well in theory it will be to short to see it I guess). Now make the distance longer and the lightspot grows and becomes less intense at the same time. But it,s still about one quantum.
Now look to the light with a telescope where would the "lost energy" be ? No event is exclusive for one viewer even if it is about one quantum. |
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| Janus |
| Posted: Thu Feb 25, 2010 5:55 am Post subject: |
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| Ghrasp wrote: |
Suppose you have a installation as with the double split system. There is a screen with two slits and one photon goes thrue both slits at the same time. Suppose you,re looking through one of these slits as a window and someone else is looking through the other slit. In astronomy the screen can be replaced to two telescopes. So the one next to you can see the same photon.
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No, only one telescope will see the photon. This the same as the experiment where you put a detector at each slit of the screen to measure the passage of the photons. Each photon will be measured as passing through only one slit and the interference pattern is no longer formed. Remove the detectors and the pattern returns.
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| Ghrasp |
| Posted: Thu Feb 25, 2010 7:00 am Post subject: |
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Most events we see involve a multitude of quanta. You can lower the multitude and come to quantumscale. The way you imagine it if an event happens on quantumscale (only one quantum) it could be seen by only one observer in the universe and if that observer has two eyes he could only see it with one eye (?)
I thought the essence and mystery of the experiment is that it even works with one quantum (from the perspective of the activator/source).
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| The wave nature of light causes the light waves passing through both slits to interfere, creating an interference pattern of bright and dark bands on the screen. However, at the screen, the light is always found to be absorbed as though it were made of discrete particles, called photons |
With this quote from wikipedia, I think you forget the "as though" part in the last sentence where I would underline that. |
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| MagiMaster |
| Posted: Thu Feb 25, 2010 4:33 pm Post subject: |
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I fully support Wiki, but I wouldn't take it's word as law.
You're failing to grasp the weirdness of QM. If there are detectors at each slit, then one one will register a single photon with equal distributions. If there is are detectors behind the slits, they will register each photon, one at a time, but in a pattern that shows wave-like interference patterns. In neither case will a detector off to the side register anything. At the quantum level, nothing is distinctly a particle or a wave and there is no "as though". It really is that weird. |
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| DrRocket |
| Posted: Thu Feb 25, 2010 4:38 pm Post subject: |
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Forum Radioactive Isotope
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| himnextdoor wrote: |
How big can a photon be?
Is it not the case that each photon-producing event causes an electro-magnetic wave to propogate through space?
One photon-producing event, one photon, one wave?
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NO.
An electromagnetic wave consists of a great many photons. |
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| Waveman28 |
| Posted: Thu Feb 25, 2010 6:10 pm Post subject: |
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| DrRocket wrote: |
| NO. An electromagnetic wave consists of a great many photons. |
I strongly beg to differ. Single photons cannot have a frequency, wavelength, a phase or even an amplitude, which are all well known properties of light, it just makes no sense. The wave model of light is much more logical and correct. The photon concept arose during the irrational era of quantum mechanics, and should be avoided. Lets face it, light is a wave: How can photons explain interference patterns? How can they explain refraction? How can they explain standing waves? How can they explain phase change upon reflection? How can they explain polarization? This list goes on and on. Light MUST be a wave. We made an error by changing our model because we misunderstood one thing: the photoelectric effect. We call light a particle to suit one experiment, which then contradicts HUNDREDS of earlier experiments. Even worse, some people think that light is both a particle and a wave, and this is just delirious.
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| himnextdoor |
| Posted: Thu Feb 25, 2010 7:00 pm Post subject: |
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Okay, bear with me for a moment.
The middle star in Orion's belt is called Alnilam. Its radius is 44 times that of the sun and it is over 1300 lightyears from earth. It is the 30th brightest object in the sky and can easily be seen with the naked eye.
Imagine that Alnilam is at the centre of a circle with a radius of 1300 lightyears and that the earth lies at a point on that circle. Dividing the diameter of the earth into the circumference of the circle and expressing as an arc tells us that the earth represents an angle of 2.163 x 10 raised to the power of -7 seconds of a degree. This equates roughly to 11.5 metres at the surface of the star.
Assuming that the photons are emitted perpendicular to the surface of the star, it would appear that all the light that arrives at the earth's surface from Alnilam originated from a circle with a radius of 5.75 metres. That is a lot of dispersion.
Given that the light has to penetrate the atmosphere, shouldn't photons from Alnilam be rare at the earth's surface? How come it doesn't blink as I move around?
And if was twice as far away, I think I would still see it. |
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| Dishmaster |
| Posted: Fri Feb 26, 2010 1:13 am Post subject: |
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| himnextdoor wrote: |
Okay, bear with me for a moment.
The middle star in Orion's belt is called Alnilam. Its radius is 44 times that of the sun and it is over 1300 lightyears from earth. It is the 30th brightest object in the sky and can easily be seen with the naked eye.
Imagine that Alnilam is at the centre of a circle with a radius of 1300 lightyears and that the earth lies at a point on that circle. Dividing the diameter of the earth into the circumference of the circle and expressing as an arc tells us that the earth represents an angle of 2.163 x 10 raised to the power of -7 seconds of a degree. This equates roughly to 11.5 metres at the surface of the star.
Assuming that the photons are emitted perpendicular to the surface of the star, it would appear that all the light that arrives at the earth's surface from Alnilam originated from a circle with a radius of 5.75 metres. That is a lot of dispersion.
Given that the light has to penetrate the atmosphere, shouldn't photons from Alnilam be rare at the earth's surface? How come it doesn't blink as I move around?
And if was twice as far away, I think I would still see it. |
What you describe is the inverse square law. This is exactly how the brightness of stars is defined. The intensity of light (= incident rate of photons) is proportional to the square of the distance between source and detector. This is equivalent to the fact that the intensity is proportional to the area penetrated by the electromagnetic wave front. |
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| Ghrasp |
| Posted: Fri Feb 26, 2010 1:46 am Post subject: |
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| Quote: |
| You're failing to grasp the weirdness of QM. If there are detectors at each slit, then one one will register a single photon with equal distributions. If there is are detectors behind the slits, they will register each photon, one at a time, but in a pattern that shows wave-like interference patterns. In neither case will a detector off to the side register anything. At the quantum level, nothing is distinctly a particle or a wave and there is no "as though". It really is that weird. |
I dont see it as weird more like mystery. Way I see it is not as different as when poales stand in a lake and waves come through. You would expect the poales to cut the waves but they aren,t cut behind the poalles, only locally at the poales (screen) they come through it as a whole again. Look at the patterns as the ways to solve it.
But anyway then you are still implying my one eye sees different events then my other eye ? Because foton emission is often regarded the emission of one foton corresponding with one event on quantum scale. When such an event happens only one person could see it ? That really is weird (and I cannot believe it I,m sorry).
I would never use the word faillure though regarding annyones attempts to understand things. |
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