Just a minor point of clarification. From B's perspective B's clock ticks normally (of course) and A is seen to tick slower (deeper in the gravity well). From A's perspective A's clock ticks normally (of course) and B is seen to tick faster (farther out in the gravity well). I'm sure that's what you meant.
by funkstar: "The velocity time dilation effect known from str is less than the gravitational time dilation effect of gtr, in which clocks deeper in the gravity well tick slower than those higher up. Gravitational time dilation is antisymmetric, meaning that this will make B's clock tick faster than A's, from both perspectives." ================================================================ Yes, I agree completely with what you stated. The faster beat of a clock higher in the gravity well is empirically measured through GPS, among other experiments. My question, however, was about the path of the light in a light clock.Relative motion of a light clock extends the path light must travel in the moving frame relative to a frame assumed to be at rest. This causes the moving light to beat relatively slower than a light clock in a rest frame. Assume the observer is in a rest frame on the surface of the Earth. What path does the light take in the orbital frame to cause it to beat faster than the Earth clock? Either the distance travelled must contract or the speed of light must increase. Lorentz contractions are only along direction of travel, not orthogonal to direction of travel as in the light clock example. ------------------------------------------------------------------------------ by funkstar: "If you know the clock's velocity relative to your own reference frame, then you can cancel out the Doppler effect. I didn't see any actual empirical evidence presented... " ============================================================= If you cancel out the Doppler effect, you are then left with clocks which beat in synch. That was my point. The actual empirical evidence is from GPS modelling of frequency changes in the signals broadcast from the satellites. NASA also uses frequency changes in signals broadcast from satellites in their deep space network to determine the location of distant spacecraft which are too distant for radar ranging to work. Can't bounce a radar signal off a Pioneer spacecraft because they are too distant to pick up the returned 'bounce'.
geistkiesel: How do we know that the embankment doesn't accelerate? I'll answer for you. You ASSUME you are looking from a reference frame in which the embankment doesn't accelerate. i.e. you prefer the embankment frame, without even saying so explicitly. In fact, I'm beginning to wonder whether you actually have the mental agility to deal with multiple reference frames, or whether in fact you can only handle one. I notice you completely ignored my post in which I showed you the correct analysis of your problem involving reflection of a photon by a mirror. Presumably, you just didn't understand it, so you decided to ignore it. If not, perhaps you can show me where I made a mistake in that post.
Get real Guys there is no such thing as a frame. Frames are used to protect pictures and photographs. Just forget the frames and watch science as it is.
Really stupid questions do not rebut concepts. Pick any point. Was that to difficult.? Actually it is easier than to claim a rocket sent from earth can rightfully claim he is at rest. When things get to hard you just refuse to answer and ask stupid questions or make snide remarks. If you were to learn somthing you could figure it out for yourself. James R: "But Mom, I've been sent to higher school I must therefore be smarter , hence I am right. It doesn't matter that I can't answer this crackpots challenges, he's just a crackpot and I'm educated."
I'll say it once more, since I have responded to this by you before. We only have a symantical differance. Your indepth presentations of the system has been very informative. However, to reduce the arguement to it's core and not fill two pages of detail I prefer to hit the highlights where the inconsistancy between GPS findings (emperically) and SRT theory are most clear. The value WAS found emperically. It was not a test that produced a velocity result directly but was a result of velocity (or orbit) and the response of clocks such that a workable distribution between GR affects and velocity affects were established to produce a workable system. Does this meet your approval? I hope so because the issue is that the velocity considered is not one of relative velocity according to SRT and that SRT produces an incorrect value, not how the value -7.2 was derived.
Anomalous: Perhaps you should try to learn some science before you make comments like this one. You could start by reading my informative thread titled "What is a reference frame?", which is conveniently linked from the Physics Forum FAQ thread (sticky). Happy learning.
MacM: If I am free to pick any point, then no point is more special than any other point. Which is exactly what relativity says. Make up your mind what you think. Stop flip-flopping. So you don't know. I thought so. You're all hot air and no substance. MacM, you know that I have never referred to my "credentials" to support any argument I've made here. Argument by authority is a very weak form. I know it is all you have to rely on. You can only refer to yourself as an authority, since nobody else on Earth agrees with you. I can refer to the entire mainstream physics community which agrees with me, but that is still argument from authority, and you can easily argue that they are all wrong, too (which you do). So, what I always do is to explain in careful detail why you are wrong, and what your mistakes are. That you continually deny I do this just makes you look pathetic, since the evidence is there for all to see.
You're trying to interpret the gtr gravitational time dilation as an str effect, which doesn't work. General relativity is a lot harder to conceptualize than special relativity, but gravitational redshift is a direct result of the equivalence principle: Everything in a gravitational field experiences the same acceleration (everything follows geodesics in spacetime). So a photon is redshifted when climbing up in the gravitational well, and blueshifted when falling into one. Now, as you noted, the frequency of light is directly proportional to time, so from the surface of the earth, the light defining a second, is strectched to being slighter longer than had the light originated higher up in the gravity well. So from the surface of the earth, the GPS clocks will tick faster, because the light defining a second in the GPS clock frame, will be compressed slightly when falling down the gravity well, and therefore arrive slightly faster than once pr. second (see below.) Cute, no? (It's slightly difficult to put the picture I have in my mind to words, so if you don't quite get it, perhaps someone else will contribute their version...) Hold on. Yes, if you cancel out the Doppler effect from the satellites then you are left with clocks that beat in synch because that's how they were designed! The standard second aboard the GPS satellites is not 9192631770 beats of the particular radiation, but slightly longer in order to cancel out the predicted time contraction aboard the satellites. The fact that GPS actually works is in itself enormously corroborative evidence of relativity theory. Despite what MacM will tell you about Tom van Flandern. In fact, paraphrasing Wikipedia, in order to give 10m accuracy, the clocks have to be synched to within 30ns. The relativistic effect is on the order of 38,000 ns pr. day IIRC.
Hey, Mac, Do you really think it's dumb to claim a rocket speeding away from earth is "at rest"? Do you think it's dumb to claim that you are at rest, sitting at your computer? Did astronauts on the moon think it was pretty dumb to imagine themselves at "rest" on the moon? It must be really dumb to imagine you're at rest in an airliner doing 600mph, even though on a calm day in level flight, you can't tell if your sitting on the runway or in mid-flight (duh, open a window! boy, you must really be dumb SL) What about people at different altitudes on the earth Mac? Say sea-level vs a mountain top community? They both have different rotational velocities. Which one's at rest? Huh? So, I'm sure you will explain your "third reference point" theory. You claim your view is superior, yet you always have to bring in a third point. I can do it with TWO points only. And get the correct results. And don't mention "reciprocity". It dosent exist.
In that case, there's no such thing as a number or language either. We're talking constructs designed to model something. A frame is an excellent tool in modeling how things relate to one another. Ignore it if you wish.
Yep. Because it is not. Yep. Because I am not. Nope. One can imagine anything they like. Declaring it a physical reality however is not only invalid but dumb. Nope. Imagine all you like just don't tell me the airliner going 600 Mph is standing still and then use that to compute some affect on another object with relative motion. quote]What about people at different altitudes on the earth Mac? Say sea-level vs a mountain top community? They both have different rotational velocities. Which one's at rest? Huh?[/quote] Now this is what we call dumb. NEITHER. The point is you can't, except in special cases and then only with regard to the correct assumption of which is at rest. Choose the cosmic muon as being at rest and show me the earth clock ran slow please. :bugeye: Seems the muon might have trouble making it to the surface if it's clock were running faster than the earth clock. Hmmmm. You are learning.
by funkstar: "Hold on. Yes, if you cancel out the Doppler effect from the satellites then you are left with clocks that beat in synch because that's how they were designed! The standard second aboard the GPS satellites is not 9192631770 beats of the particular radiation, but slightly longer in order to cancel out the predicted time contraction aboard the satellites. The fact that GPS actually works is in itself enormously corroborative evidence of relativity theory. Despite what MacM will tell you about Tom van Flandern. In fact, paraphrasing Wikipedia, in order to give 10m accuracy, the clocks have to be synched to within 30ns. The relativistic effect is on the order of 38,000 ns pr. day IIRC." ================================================================ You failed to mention which frame of reference you were referring to when you said the second aboard a GPS clock was not 9192631770 beats of a cesium clock, but it is EXACTLY that number of beats in the satellite's frame of reference. When compared with an Earth-based cesium clock, the satellite clock will beat faster. The 9192631770 beats of a cesium clock is always, by definition, a second in any frame of reference the clock is in. This second is relative to cesium clock seconds in different frames of reference, however. A quartz oscillator counts the frequency of cesium, or rebidium, atoms. That is where the adjustment is made to synchronize two clocks in different frames of reference. To synchronize an orbiting clock with an Earth-based clock, the quartz oscillator is set to count more beats (the frequency) of the cesium atom to synchronize with the Earth second. A frequency generator can then send a signal based on this adjusted frequency, or can further adjust the transmitted signal up or down in frequency to correct for other effects known to affect the signal in transit to the Earth, such as ionospheric delays. The ionosphere has the greatest effect of any on the signal-in-transit, varying from a few meters error to more than 30 according to the density of ionized oxygen molecules and electrons in the ionosphere. The ionosphere is a plasma that varies in density. I already know of van Flandern and give no credience to what he says. In reference to the light clock, the light clock MUST agree with a cesium clock in the same frame of reference (in vacuum) or time itself is not relative to location and motion. If a cesium clock beats relatively faster in a reduced gravitational potential, the light clock must also 'beat' faster in the same location or it isn't time the cesium clock is measuring, but a change in physical properties of the atom, a change in physics.
Did you mean this comment to be an insult? It isn't because: 1 - I have stipulated relativity is at work in GPS. Just not SRT as advocated. 2 - I have never once quoted Tom Van Flandern. What is your problem. Don't have sufficient rebuttal without fabrication or slander?
Well, that's it then. This is the essence of our modern understanding of the universe of motion. Any object in a state of uniform motion can be considered to be at rest in it's own frame. MacM thinks the airliner has some intrinsic absolute motion and would never think of using it as the v=0 reference frame for measurements or calculations as they would be invalid. I for one am tiring of this stupid discussion. What more can we learn from countering MacM, Geist, et al? I'm thinking about quitting this career of defending that which needs no defending. If MacM an Geist were school students of mine, I would long ago have submitted them to testing for special education. Is this harsh? No way. If blind stubbornness is a virtue, then these two have made it into a religion.
MacM: Ok, time for another summary of your position. According to you: You are not at rest sitting at your computer. Astronauts standing on the moon are not at rest. Passengers in an airplane are not at rest. People living at sea level or on top of a mountain are not at rest. Nobody is at rest, according to you. (Or are they?) Yet, I still think you would say that time dilation really happens for the person standing on the ground at sea level watching a plane fly past. Why do they get the correct "gamma" value, since according to you the ground is not at rest?
Unbelievable, truely unbelievable. People can become so confused and brainwashed to believe that they can state in the same sentance that something has a velocity and is at rest at the same time. Listen to yourself. Think about the reality of what you are saying. Certainly, as I have said we have no current method of determining absolute rest or motion but it is pre-kindergarten child like mentality to think you can claim something physically at rest and in motion at the same time. The reality is the only evidence of gamma emperically has involved specific cases such as cosmic muons or particles and accelerators. Cases where a third point (the observer - you) is at rest with one of the components being calculated - i.e. the accelerator or the earth surface clock. In such cases the gamma will calculate correctly. However in every other gendankin you can create where a third point is used it demonstrates that the correct methodology is not relative motion but the gamma effective which is the ratios of gammas of the respective velocities of the two components creating the collective relative velocity. A procedure which also prohibits the false and unsupported concept of reciprocity; which is further supported by actual physical evidence - GPS. Now which of us actually has the stronger hand? Hmmmm. HeHeHeHe. What a joke. And you guys think you are superior? :m:
And I guess it is pre-pre-kindergarten to imagine that physicists actually say that. Nothing can be at rest and in motion at the same time, in the same reference frame. The only way anybody could be confused about this is if they didn't understand reference frames. Oh, I see what the problem is...
Yes the problem is that your referance frames dodge doesn't hold up with actual accumulated time on the clocks. Think GPS. Remember that relative velocity does not compute time dilation correctly. Remember that reciprocity has failed to ever be observed and is physically impossible. Then think how is it possible to support a theory that doesn't hold up and is shown false by physical evidence.
