Redshift and speed of light

Saiph · Sep 16, 2004

larper, I believe he was saying <blockquote>In reply to:<hr />You're now close enough to [saying], in your parlance,....<hr /></blockquote> He wasn't refering to distance. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

siarad · Sep 16, 2004

<blockquote>In reply to:<hr />Nope. Still wrong. Distance has nothing to do with the frequency at which they are returned to you<hr /></blockquote> That's exactly my point, the number of balls received can't exceed the number thrown which is what Saiph said. The return frequency is the same as the sent one but it is modulated by motion. I previously posted how to derive the speed from this by integration. Further showing that neither distance or speed of transmission mattered. The Police RADAR or submarine ASDIC doesn't care about distance, how did we get from balls to continuous waves anyway.

Saiph · Sep 16, 2004

how'd we get there: Simple, the balls represent an individual wave crest in a continous wave. I agree, you can't throw more balls than you have. However I'm not throwing more balls than are thrown! I'm merely running up and catching them enroute. Fast enough that they don't travel the same amount of time in the air. The first one travels 10 seconds, the next 9, the next 8, the next 7, because I close the distance between the balls so they don't have to go as far as the previous ones. Then, once I catch one, I throw it back. And each time I throw one, the distance is less, so they don't have to travel as long. Work some numbers out! Throw a ball 100 ft at 10ft/sec (yeah, slow I know, but any numbers will do!) every second. Then have someone close the distance at 10 ft/sec. See what you come out with. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

larper · Sep 16, 2004

Give it up Saiph. He is just arguing for the sake of arguing. <div class="Discussion_UserSignature"> Vote Libertarian </div>

siarad · Sep 16, 2004

A wave can return more crests than transmitted, Doppler shift but balls can't. You even posted a link showing distance was immaterial & then post an example. The time of travel or distance can't affect the number of balls returned so their frequency isn't changed only the relationship This is just distorting the topic but balls aren't a good simile

Saiph · Sep 16, 2004

actually, a wave can't return more wave crests than transmitted. I never said distance was material. I merely gave a distance for you to figure out the various relationships. That distance actually ends up factoring into the velocity. If you'd like you can ignore it completely, and just say its 10ft closer each time (that's velocity dependance there) and run the series to infinity. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

newtonian · Sep 18, 2004

Igorsboss - That's new to me, that doppler effect is from time dilation. In a formula (simplify if possible) how would you distinguish time dilation variable from speed variable? Couldn't you introduce either in the formula and get the same result? Speed (relative, with two reference points[or more]) is the cause, time dilation is the effect - correct? And then the doppler effect comes from both in a sequence of cause and effect- or did I miss something? And I fail to see the difference between this effect on light and on sound. {I'm not disagreeing, simply do not understand.} For example, both in the case of sound and in the case of light, the frequency is not changed by the speed of the source from the source as a reference point. Rather, the frequency is changed by the relative motion (and time change) between two reference points [or more]. You all - balls? I'm considering sound and light as waves, not particles, when studying red shift and doppler effects. BTW - there is a photon, but not a soundon- correct? BTW#2-some scientists are considering the speed of light may not be constant.

unclefred · Sep 23, 2004

You are correct that there is no relationship between speed and frequency such that one can predict one from the other. If one were given a certain substance (say glass) and given a particular frequency (say red light), one cannot predict the speed of light. However, there is a relationship between the speed and the frequency such that different frequencies travel at different speeds. Given a medium (say glass) and given a specific frequency (say red) one can look up the speed that it will travel. For most mediums (vacuum is a notable exception) every frequency will travel at a slightly different speed. This is known as dispersion (a web search will produce lots of references and equations but here is one http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/dispersion.html). It is precisely the different speeds that cause chromatic aberration and also allows optical designers to produce color corrected lenses. Light is different from sound in that it sometimes behaves like a wave and sometimes behaves as a particle. This duality is unique to light. However, when it is behaving like a wave it follows all the normal rules of waves (velocity, frequency, etc.). One of these wave rules is the Doppler shift. The Doppler shift phenomena applies to light just the same as it applies to sound.

CalliArcale · Sep 23, 2004

<blockquote>In reply to:<hr />BTW - there is a photon, but not a soundon- correct? <hr /></blockquote> That is correct. Sound waves, unlike EM waves, are really just compression waves. Any compression wave can be considered sound, including those in such insubstantial media as the interstellar medium. It's just got a really really really really really long wavelength. I'm afraid the rest of the questions in your post are way past me, though. <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> "People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff." -- The Tenth Doctor, "Blink" </div>

Saiph · Sep 23, 2004

Actually, there is a relationship between speed and frequency for light that includes different mediums. V=C/n where N is the index of refraction of the medium. Now, N varies with the wavelength, but there are mathematical approaches to calculating even that (Heck, I did that just the other day for a class). Since that is calculable, you can calculate the speed of any wavlength. So, you can predict the speed of light, even without tables generated purely on measurement. <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

igorsboss · Sep 25, 2004

Sorry for the delay. I am travelling, so I don't have my textbooks handy for cross-checking. I'm also using a laptop, and I hate typing on laptops... I should be more precise. The doppler effect comes from two effects. The first, classical, effect is described in posts by others in this thread. The second, relativistic, effect is time dilation. This is noticed when the source and reciever are moving at significant fractions of the speed of light relative to each other. The formula I posted earlier is from special relativity. At slow speeds (where v<<c), the formula becomes the same as the classical formula. At relativistic speeds, the formula accounts for the fact that nothing can exceed the speed of light. Whenever you are talking about doppler shifts of light beams, it is wise to always use the relativistic form to avoid any accidental miscalculations. Now, how do I explain the time dilation doppler shift? Stay tuned...

igorsboss · Sep 25, 2004

That's new to me, that doppler effect is from time dilation. Put your thinking cap on for this one... First, re-read my earlier post, the one with the doppler formula in it. Now take special note of my earlier the comment which talked about the case where theta was exactly 90 degrees. What does theta=90 degrees mean physically? Well, it means that one frame of reference is moving in a circular path around the other. Now, if one frame of reference is moving in a circular path around the other, then the distance between them must not be changing. The classical doppler shift formula in this case says that since the distance between the frames of reference is unchanging, then there is no doppler shift. But this is not correct!!! Since the frames are moving relative to each other, special relativity demands length contraction and time dilation. Since time is moving slower in the moving frame of reference, there are fewer wave crests happening per second (per second in the stationary frame). Fewer wave crests per second is observed as a red shift in the light's frequency. So, here is a case where the classical doppler theory would predict no doppler shift, but special relativity predicts one. The relativistic model is the one that agrees with observation. Note that observers in frame S will observe a red shift from frame S', and that observers in frame S' will also observe a red shift from frame S. Go figure! In order to observe motion but no doppler shift, the frames of reference must describe a spiral (Spira Mirabilis, I think, but I haven't proven that) as they approach each other, so that the blue shift from the approach angle equals the red shift due to their relative motion. In a formula (simplify if possible) how would you distinguish time dilation variable from speed variable? Couldn't you introdu

newtonian · Sep 25, 2004

Igorsboss- Well, the trinity illustration doesn't work for me. I used to be Lutheran but could never make sense out of that doctrine. Isaac Newton rejected the Trinity doctrine, and so do I and my religion. In effect, I believe the Father (Jehovah) caused the Son (Jesus) which is why they are called father and son. That being said, I think I see your point- scientifically. And thank you for distinguishing relativistic doppler and classical doppler. I disagree, though, on the lack of a causal relationship. My viewpoint is that speed (velocity?) is causing doppler effects - both classical (Newtonian?) and relativity based. And your point about circular motion high speed causing red shift brings up another question: Is our universe spinning so that some of the red shift is due to high speed circular motion rather than actually increasing distance? I think the answer is no, btw. After all, spin would decrease with expansion, while spin increases with contraction. Perhaps more of a valid question: was our universe spinning at all at the Big Bang? In that case, it would be spinning more the farther out, = farther back in time, we look with our telescopes.

newtonian · Sep 25, 2004

stevehw33 - all seriousness aside: Either you misunderstood unclefred or you are suggesting the existence of a soundon! Seriously, how would you define a Debroglie wave?

Saiph · Sep 26, 2004

There is not soundon. Steve was merely saying the particle wave duality is not unique to light. It's also present in matter (as it should be since, E=mc^2). The De' Broglie wavelength, by the way is: W=H/mv W=wavlength, H=planck's constant M=mass of object V=velocity of object OR w=h/p p=momentum (=mv) <div class="Discussion_UserSignature"> --------------------SaiphMOD@gmail.com -------------------"This is my Timey Wimey Detector. Goes "bing" when there's stuff. It also fries eggs at 30 paces, wether you want it to or not actually. I've learned to stay away from hens: It's not pretty when they blow" -- The Tenth Doctor, "Blink" </div>

igorsboss · Oct 1, 2004

Well, the trinity illustration doesn't work for me. Ok. I'll try another illustration. Consider a cut diamond held loose in your hand. The cut of the diamond defines a relationship between each of the facets. It is not possible to move one facet of the diamond without moving all of the facets of the diamond simultaneously, except by destroying the gem altogether. To interpret this illustration, consider that speed, time dilation, length contraction, and the doppler shift each have a definate relationship with respect to each other. This relationship is the gem as a unified whole, with speed on one facet, time dilation on another facet, length contraction on another facet, and the doppler shift on yet another facet. The gem looks different from different viewpoints, but regardless of how you look at it, it remains the same gem. Any attempt to change one facet, by turning it in your palm, for example, results in a change in all the rest. That being said, I think I see your point- scientifically. And thank you for distinguishing relativistic doppler and classical doppler. Sure. My viewpoint is that speed (velocity?) is causing doppler effects - both classical (Newtonian?) and relativity based. My viewpoint is that this is tantamount to saying that you insist on always looking at the whole diamond through a single facet. I agree that we are looking at the same diamond. I can even look at the diamond the same way you do, from time to time. However, I find this viewpoint narrow and boring, for I have already seen many of the other sparkles this gem has to present, and I'm encouraging you to see the beauty also. Yes, I suppose that changes in facet 4 cause changes in facet 18. However, I would rather notice that the whole diamond is merely turning in my palm.

newtonian · Oct 1, 2004

ricimer- thank you. I intend to research those waves further. igorsboss - Makes sense. So who is turning the diamond? And who cut it? And who created its properties so that they would be so linked? Of course, I agree that physics and our universe is awesome and beautiful. However, I cannot see how time dilation would cause speed. It seems to me to go only the other way. Did I miss something? In other words, the cause is the change in relative distance during time (or appearance of time) between two reference points. And there must also be a cause for this change of relative distance. On redshift and the speed of light: Time only goes one way. However, the shifting can go both ways - blue or red. I assume this is because of the difference between appearance (from different reference points) and actual sequence.

Redshift and speed of light

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