I disagree. He’ll never be convinced but it does end up being a good physics lesson for those who follow along.
Indeed. I’ve learned a lot trying to find ways to explain these problems to myself and others. Someone with a preconceived notion they’re not willing to let go of might not learn anything, but many of the rest of us have.
You all seem to think that I had made up my mind long ago about everything that is going on in this forum. That is not so. When I started this discussion (or perhaps joined in), I did have one basic starting point, and that is that relativity is wrong, and local aether theory (or speed of light relative to the local gravitational field theory) is probably correct. I have not changed my mind on that, but through this discussion I have enlightened myself, and some of you, as to what actually is going on on our planet, and some of the ramifications of SRT.
For instance, I have not “finally realised I was wrong on frequency change with change of speed” Which Zenbeam posted. The wording “finally realised” is totally wrong and infers that this is a long held belief, which it is not. I opened up that subject not knowing any answers as I had never before asked the question. I had just assumed, as I suspect most of you had, that the speed of light in our atmosphere was c/n regardless of direction. Because of working through (sometimes tortuously) the questions and answers, and digging deeper than most people would do, and yes - playing Devil’s Advocate, unforeseen answers came to the fore.
As recently as May 17th, Trinopus was still of the opinion that the speed of light here on Earth is c ( c/n ) in any direction.
Originally Posted by tomh4040
. . . If the radar increases its velocity . . .
Trinopus reply “Isn’t this the core of the issue? According to SR, this doesn’t happen. It’s also never been observed to happen.”
Have you learned something from this exchange Trinopus?
It took over two months and who knows how many posts for what’s a very basic relationship. I stand by “finally realized”.
Um… No, sir. I stand by what I wrote. Can you please explain your reasons for disagreeing in precise terms? Because, as far as I know, the radar beam does not increase in velocity. SR says it doesn’t, and observation does not show it to.
(Yes, I know, it changes velocity, by changing direction. But it doesn’t increase velocity. That implies an increase in the absolute value of the magnitude of the vector.)
On the Straight Dope, asking people, “Do you see my point now?” has been shown to be a really, really rotten debate technique. It’s your duty to make your point clear, and to defend it when it is questioned.
Trinopus, it is your duty to read the posts, and not to make (deliberate) inaccurate statements such as the one above attributed to me. I have never said that. I have answered this point quite clearly many times on this forum. For your benefit, as you have apparently missed it, I will answer it again, but if you care to look back over my posts you will find the explanation there. Bear in mind that this is the relativists explanation, not mine.
SRT says that the speed of light is c relative to any and all IFRs. The Earth is not an IFR, it is an RFR. That is an acronym which I have coined to differentiate it from other non IFRs such as a linearly accelerated frame of reference or an AFR. Restricting our discussion to east west travel at the equator, in order for the speed of light to be c relative to an IFR, it cannot be c relative to the Earth, as the Earth is an RFR. Because of the rotation of the Earth, a light beam split and sent round the Earth in opposite directions will not arrive back at the starting (entry/exit) point together. The beam going west to east will have further to go than its counterpart sent east to west and therefore take longer. This is because relative to an IFR, the Earth has rotated while the beams were circumnavigating, so shortening the east to west path and lengthening the west to east path. That is how a ring laser works.
That description is when looking from an IFR. Looking at what is happening from here on Earth, and making all measurements relative to the Earth, the beam of light traveling west to east has exactly the same distance to travel as the beam of light traveling east to west. As the east to west beam arrives back at the entry/exit point before the west to east beam, its speed was faster. There are therefore two speeds for light, with the caveat that we restrict our discussion to the equator.
If you are still of the opinion that the speed of light is c on the Earth, then by definition it is c in an RFR. If light is c in one RFR, it must be c in all RFRs. It cannot be c in a rotating ring laser (which is an RFR while it is rotating), or the two beams would arrive back at the entry/exit point together whether the device was stationary or rotating. They arrive back together if the device is not rotating (when it is an IFR), they do not arrive back together if it is rotating (when it is an RFR).
This is covered in the Wikipedia article already referenced on the subject, and is also agreed by your fellow relativists here on this forum, so you really are alone in this.
Wiki quote “If a number of stations situated on the equator relay pulses to one another, will the time-keeping still match after the relay has circumnavigated the globe? One condition for handling the relay correctly is that the time it takes the signal to travel from one station to the next is taken into account each time. On a non-rotating planet that ensures fidelity: two time-disseminating relays, going full circle in opposite directions around the globe, will arrive at the originating station simultaneously. However, on a rotating planet, it must also be taken into account that the receiver moves during the transit time of the signal, shortening or lengthening the transit time compared to what it would be in the situation of a non-rotating planet.”
From a fellow relativist :-
I find some fundamental flaws in thought processes in this thread. If anything relativity really shows the problems of scientific observation than it does about reality.
In the example of a person traveling to a near star system at the speed of light and returning. The person will return as exactly aged as those that stayed on earth.
However, on earth they could show a second instance of the astronaut to himself through a telescope at a younger age. He would be observing himself in space time and mathematically that is what a scientist would get on his calculations.
The light reflected from the astronaut is just a hologram. Unfortunately Physics needs two things in which to observe events; matter as in machinery in which to collate information and light in which to observe (anything at a distance anyway) It cannot observe events other than that and is therefore limited in viewing reality.
Any instance in the universe can be observed by infinite amounts of perspectives with different results and none gathering an idea of reality as it actually happens unless it reverse calculates to compensate for distance and speed of light.
The problem is matter cannot travel at the speed of light unless it is in the form of energy which Einstein correctly postulates as E=MC2, So only light itself and its own speed can be used to correlate reality.
No, but it does show the difficulty of trying to explain the concept of relativity.
Often when a relativistic thought experiment is described to someone who is new to relativity, they object with something like “But that is just the light!” – because it sounds like a sleight of hand, it sounds like we’re saying because light has a transit time then that in itself is time dilation. It’s not what relativity is, but that’s how it often comes across.
I remember being told about someone travelling faster than c and why it implies time travel: but it was a badly described example and just sounded like someone seeing a set of events that had already happened in reverse order – that’s not time travel – and it therefore took me a while to grok the time travel case.
But the important point is that light itself is not special here, c is. You could basically see relativity as space and time being warped to preserve the invariance of c in all reference frames.
This is incorrect – time is warped and the astronaut does actually age less.
This is incorrect – he was travelling at less than c and the light from any part of his journey has already reached earth before the astronaut.
Well said. Welcome to the forum. I am a heretic and a renegade, and so far, all the venom of the relativists has been aimed at me. I see you are a heretic and possibly a renegade also, so you may well attract some venom. There seems to be plenty to go round!
I have never deliberately misattributed anything to you or to anyone else. If I have been in error, it has been honest error, and NEVER malicious disregard for the truth.
You have not been sufficiently clear.
The Sagnac effect applies to completed paths around a ring. Not merely to light going east or west, but to light that goes around a closed path, in a ring.
Light that simply goes east, then west again, is not affected by this effect. The Michelson Morley experiment does not show any difference in speed of light beams that go east then west again, as compared to light that goes west, then east again, or north, then south.
The Earth is both an RFR and an IFR, depending on what you happen to be measuring.
Yes. When the light goes in a complete ring.
This does not apply to Earth as an IFR. Light that is sent out in a straight line, and reflected back again in the same line, moves at exactly c. This supports Special Relativity.
We are in agreement. The M/M experiment, conducted in an IFR, supports the Lorentz Transformations of Special Relativity. Time, Distance, and Energy are compressed. The moving astronaut ages more slowly than the stationary astronaut.
The effect of a ring laser does not disprove any of this.
So…what are we disagreeing about, exactly?
I don’t think this is correct.
To begin with, let’s have the astronaut move at .99c, rather than at the speed of light. Moving at 99% of the speed of light is possible (although hideously expensive!) for a physical object. Moving at the speed of light is believed to be impossible for a physical object.
Now: he goes to Alpha Centauri and back. Say, 4.00 light years for convenience. It takes him 4.04 years, each way. By the Lorentz equations, he only ages about half a year on each leg of the trip, so after the eight year round trip, he’s only aged one year.
Now: exactly how do you propose that “they show a second instance of the astronaut to himself through a telescope at a younger age.” I don’t understand what you mean by this.
Once he has returned, he isn’t in space any longer, and so they can’t “show” anything to him. He’s here.
When he is in space, yes, he can send pictures of himself back to earth. People on earth can send him pictures. They can send him pictures of New Year’s Eve, 2013, 2014, 2015, 2016, etc. He is amazed, as these “years” seem to him to be a month and a half apart.
He can’t send a picture of himself to himself. The light waves of the tv transmission move faster than he is moving.
He could send a messenger rocket to himself, but this would add additional complications; you’d have to calculate the speed of this messenger, and how it related to all the other frames of reference. It’s pointlessly messy.
Not a hologram, exactly, but let’s simply say a light-image. This is well understood. When we look at Alpha Centauri, we’re seeing light that is four years old. We’re seeing the light-image of AC. We can’t see AC as it is “right now,” because it takes four years for the light to get here.
Generally true. Alpha Centauri might have gone supernova three years ago, but we wouldn’t know it for another year.
What Relativity tells us is that events that may seem simultaneous in one frame of reference may seen non-simultaneous to another frame of reference.
Again, I’m not totally clear what you mean, but I think I agree. We have to calculate events based on the relative speeds of various frames of reference.
You and I might be in the same place at a specific instant, but you’re stationary, and I’m moving very, very fast. We’re both watching two distant stars, which go supernova. You might see them both go supernova at the same instant; yet I might see one go supernova before the other one does.
Neither of us is “wrong.” Both of us are right. You see two events as simultaneous; I see them as sequential. That’s the price of relativity.
My old physics prof said that if you could travel FTL, or even if you could send a message FTL, then you could travel or send a message backward in time.
I’ve never quite managed to understand this. I don’t know if it has been demonstrated using proper mathematics, or if it is an appeal to the unknown, since there is no physical meaning to the “square root of a negative number.” I’ve done a lot of Google searching on this, and haven’t seen a solid explanation.
(Meanwhile, you do have the possibility of time travel in Tipler machines and other extravagances. Fortunately, no one is likely to send a probe in a high-speed closed orbit around a gigantic, hyper-massive cylinder that is spinning at extremely high rates of revolution! Tipler, Penrose, Hawking, and others suggest that this could lead to time travel…but I think the experiment will never actually be performed!)
This argument comes about because frames of reference moving with respect to each other don’t agree on what planes of constant time would be. If you look at the Minkowski diagram at the top of that page, t = 0 in the black reference frame doesn’t agree with t’ = 0 in the blue frame.
To make it easier, imagine a signal can be sent instantaneously. In the black frame, send a signal to the right. Now accelerate to the right until you’re in the blue frame, and send a signal instantaneously to the left in that frame. It can get back to x = 0 in the black frame in the past, in that frame.
If the signals could be sent FTL, but not instantaneously, that may mean you need to accelerate a lot to send signals into the past.
It’s not strictly true that FTL signals always allows sending a signal back in time. It requires there also to be no privileged reference frame*. For example, if the black frame were a privileged frame, and these FTL signals were always instantaneous in that frame no matter what frame the sender was in, you wouldn’t be able send signals backwards in time.
- Our physics doesn’t have privileged frames, but it also doesn’t have FTL signals.
I’m embarrassed and ashamed…but honest enough…to admit I don’t understand this. Until this thread, I’d never heard of the Sagnac Effect, either.
(I’m only participating in this thread because questions have been asked which I do know the answers to!)
Oh, well… I guess I’ll just brew up a nice cup of Thiotimoline tea…
Two spaceships zip past each other at 87%c relative speed. Ten minutes after, you (on spaceship A) decide to send an (instantaneous) message to spaceship B, because their left rear light is broken. On spaceship B, from your point of view, five minutes have elapsed since the meeting, due to time dilation (at 87%c, the Lorentz factor is about 2). So the instantaneous message arrives five minutes after the meeting on B. The return message is sent immediately (‘Thx, fixed!’), and, since from their point of view, only 2.5 minutes have elapsed on your ship (since you are moving, relative to them, at 87%c and five minutes have elapsed on their on-board clock), the instantaneous message reaches you 2.5 minutes after the meeting, and 7.5 minutes before you ever sent the original message in the first place. Which you now don’t need to, seeing as how they’ve long fixed their rear light.
See also the discussion under ‘tachyonic antitelephone’.
You attributed this quote to me, but you edited a pertinent part of it out. Here is the quote again with the second part in place :-
“Because of the rotation of the Earth, a light beam split and sent round the Earth in opposite directions will not arrive back at the starting (entry/exit) point together. The beam going west to east will have further to go than its counterpart sent east to west and therefore take longer. This is because relative to an IFR, the Earth has rotated while the beams were circumnavigating, so shortening the east to west path and lengthening the west to east path. That is how a ring laser works.” That was what you quoted and is OK so far. This is what you omitted, did you agree to this?
“That description is when looking from an IFR. Looking at what is happening from here on Earth, and making all measurements relative to the Earth, the beam of light traveling west to east has exactly the same distance to travel as the beam of light traveling east to west. As the east to west beam arrives back at the entry/exit point before the west to east beam, its speed was faster. There are therefore two speeds for light, with the caveat that we restrict our discussion to the equator.”
You are forgetting a very important point here. Light always travels in straight lines (ignoring geodesics which bend the path of light very gradually and by a very small amount, and are not applicable here on Earth). When light is sent round the Earth, it uses mirrors or fibre optics. As it travels round the Earth it goes in a straight line, it is then reflected through a small angle by a mirror (or the inside of the fibre optic), then in a straight line, then reflected again until it arrives back at its starting point. In other words it always travels in a straight line. Let us assume that it travels 400 legs in straight lines, being reflected by mirrors in between each leg. Each leg is then 100 kilometers long. As the speed difference is detected at the end of the journey when the light is back at its entry/exit point, there must be a speed difference when light travels in a straight line. If there is a speed difference detected at the end of the loop, precisely when does that speed difference appear? Does it increase in 400 small increments or does it appear in just one of the 400 legs – if so, which one? No, the answer is that light, no matter how short its journey and whether it is reflected or not, has the speeds (at the equator) :-
Velocity of light west to east (VLWE) = 299,792,019.2 M/s
Velocity of light east to west (VLEW) = 299,792,946.8 M/s
The MMX does not detect a difference because it is measuring the average speed of light. The average speed east to west or west to east is the same as the average north to south or south to north.
This is preposterous, and leads to the conclusion that if an RFR can be an IFR, then a ring laser can be an IFR, and you only included it to sidestep my point which was :- “If you are still of the opinion that the speed of light is c on the Earth, then by definition it is c in an RFR. If light is c in one RFR, it must be c in all RFRs. It cannot be c in a rotating ring laser (which is an RFR while it is rotating), or the two beams would arrive back at the entry/exit point together whether the device was stationary or rotating. They arrive back together if the device is not rotating (when it is an IFR), they do not arrive back together if it is rotating (when it is an RFR).”
Please answer this question. We know that in a (rotating) ring laser the two beams have different speeds or they would arrive back together. What size does a ring laser have to be before it ceases to be an RFR and becomes an IFR so that the two beams of light sent round in opposite directions arrive back at the entry/exit point together?
The Earth is not an IFR, and the speed of light is c only in an IFR. This point has already been covered. Light going round the Earth goes in straight lines, and during each leg its speed is less than or more than c depending on its direction. If radar did not behave the same, a radar pulse sent between two mirrors alongside the light beam would not have the same speed as the light beam. This is definitely against relativity.
We are not in agreement. The MMX cannot differentiate between aether theory, or light speed relative to the source, or SRT, and it was not, and any repeats of it are not, conducted in an IFR, they are conducted in an RFR. Neither does it support time dilation et al, they are suppositions of SRT which are borne out by the mathematics of the Lorentz transformations. This is not a coincidence, SRT was invented to match the Lorentz transformations.
The ring laser proves that the speed of light is not c in an RFR. All IFRs are equal, and all RFRs are equal, so must be treated as such. The Earth is an RFR, so the speed of light (round the equator) is not c relative to it.
We are disagreeing about all the above points. Remember that I am playing the part of a relativist in this discussion.
I do not play these games.
Ask a question, and the participants here will try to answer it.
You certainly do play games. You pretend to know what you are talking about, then admit on this forum that you had never heard of the Sagnac effect before it was discussed here.
Like John Cazale, you ask questions of others, then refuse to answer ones put directly to you.