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"Can we prove light is effected by gravity?"Yes....sorry, you cannot view external links. To see them, please REGISTER or LOGIN"What if the distant observer sent a message about how the distance of the mirrors differed from his perspective as a percentage and gave instructions for the distance of the mirrors to be adjusted by that amount?"Then the clock would run at the wrong rate from the POV of the person near it.

Do you mean "affected" rather than "effected"?

If you translate this to a Higgs field, then that field acts on a few types of accelerating particles, unless they are in a 'uniform motion', in which case there is no 'interaction'. That idea guarantees geodesics to exist everywhere, although it also seem to define an absolute 'global frame of reference'. Because in such a definition a uniform motion must find itself at rest, doesn't matter from which observer, or at what velocity/mass. So it is a observer dependent absolute frame of reference, but it will be impossible to define it as a 'globally' definable field, contained 'inside' a SpaceTime.

I have just finished reading "Gravity" by Brian Clegg. This discusses some of the issues facing Einstein whilst developing general relativity. I don't think many people understand all the issues. Einstein did think that gravity could interact with itself and that there was gravitational feedback. He also included a vibrational element to gravitation. It is interesting that some of the equations, according to "Gravity", have not been solved in the almost 100 intervening years. While anyone can discuss relativity, not even Einstein understood it fully himself. We have to bear this in mind when saying something doesn't happen in such and such a way without having an in-depth understanding of general relativity.

Quote from: jeffreyH on 24/01/2014 14:37:23I have just finished reading "Gravity" by Brian Clegg. This discusses some of the issues facing Einstein whilst developing general relativity. I don't think many people understand all the issues. Einstein did think that gravity could interact with itself and that there was gravitational feedback. He also included a vibrational element to gravitation. It is interesting that some of the equations, according to "Gravity", have not been solved in the almost 100 intervening years. While anyone can discuss relativity, not even Einstein understood it fully himself. We have to bear this in mind when saying something doesn't happen in such and such a way without having an in-depth understanding of general relativity.Very good points. I try to avoid weighing in on physics topics where I don't have a thorough understanding of the material, and general relativity is one of those areas. Unfortunately, some users do weigh in with opinions without making it clear that they're not experts, and you can get a lot of misinformation in these threads about how gravity works. More unfortunately, on this forum, we don't have a general relativity expert, so I would be wary about trusting answers you get on this forum without double checking them.You make another good point about Einstein. Oddly, many threads on GR try to reference what Einstein believed. He was unarguably one of the greatest figures in the history of physics, but we've advanced quite a bit since he proposed his theory and found that he wasn't always correct and have found better ways to explain some of his ideas. Finally, regarding your question above about gravitational interaction with itself, as I understand it (not being an expert), Einstein's field equations (that describe how momentum and energy shape the gravitational field) are non-linear. This means that because a gravitational field can have momentum and energy, it can be a source of further gravitational field. This is what makes the equations so hard to solve, and in many cases solutions have to be found numerically. This is distinct from the other famous set of equations governing classical fields: Maxwell's equations, which describe electromagnetism. These equations are linear because the electromagnetic field does not interact with itself.

It also depends on what you mean with a 'interaction'. If you take a perfectly spherical shell, then we would expect no gravity in the middle. That one you either can describe as the 'force' of gravity taking itself out, or as there is no general direction for it, more than the observers own. To make a experiment of this you need a observer, defining it. That observer will have a gravitational influence, even if it is a 'test particle', assuming it to have mass. That direction is inwards, to a center.

I read the post about the photon and atomic clocks down a mine. Someone noted that to a distant observer the mirrors of the photon clock would appear further apart. What if the distant observer sent a message about how the distance of the mirrors differed from his perspective as a percentage and gave instructions for the distance of the mirrors to be adjusted by that amount? Would that give us any useful information from the perspective of the respective observers?

Quote from: yor_on on 24/01/2014 22:01:45It also depends on what you mean with a 'interaction'. If you take a perfectly spherical shell, then we would expect no gravity in the middle. That one you either can describe as the 'force' of gravity taking itself out, or as there is no general direction for it, more than the observers own. To make a experiment of this you need a observer, defining it. That observer will have a gravitational influence, even if it is a 'test particle', assuming it to have mass. That direction is inwards, to a center.I haven't had time to read your last post but this one can't be right. If gravity cancelled out at the centre of a mass there would be no gravitational collapse.

The surface of a sphere is not pressing inward, because gravity travels outwards, it is being pulled in by the attraction of the internal mass.

OK then here is the argument. Gravitational field strength is proportional to both time dilation and length contraction. The stronger the field then the more intense both these effects are. It follows that if we say the gravitational field is cancelled at the centre of a mass then so must the effects of time dilation and length contraction be cancelled. No field (cancelled out) no effect on spacetime. It cannot be argued any other way. If a force is cancelled out then it CANNOT produce an effect.

Quote from: jeffreyH on 27/01/2014 20:01:29OK then here is the argument. Gravitational field strength is proportional to both time dilation and length contraction. The stronger the field then the more intense both these effects are. It follows that if we say the gravitational field is cancelled at the centre of a mass then so must the effects of time dilation and length contraction be cancelled. No field (cancelled out) no effect on spacetime. It cannot be argued any other way. If a force is cancelled out then it CANNOT produce an effect.A gravitational time dilation and Lorenz contraction is related to mass, and, according to Einstein, to a uniform constant acceleration. Then you have 'energy', but I would prefer to leave that one aside for this as it hurts my head. But it also involves two frames of reference. Defining the 'empty center' as one frame, and the shell as another there will be a time dilation involved, as the two 'imaginary clocks' we compare between can't give us the same 'time'. Doesn't matter from where you measure, although if you measure from a center, it's no longer empty, sort of, so then we would have to add whatever mass that is to our consideration.

Quote from: yor_on on 28/01/2014 02:24:47Quote from: jeffreyH on 27/01/2014 20:01:29OK then here is the argument. Gravitational field strength is proportional to both time dilation and length contraction. The stronger the field then the more intense both these effects are. It follows that if we say the gravitational field is cancelled at the centre of a mass then so must the effects of time dilation and length contraction be cancelled. No field (cancelled out) no effect on spacetime. It cannot be argued any other way. If a force is cancelled out then it CANNOT produce an effect.A gravitational time dilation and Lorenz contraction is related to mass, and, according to Einstein, to a uniform constant acceleration. Then you have 'energy', but I would prefer to leave that one aside for this as it hurts my head. But it also involves two frames of reference. Defining the 'empty center' as one frame, and the shell as another there will be a time dilation involved, as the two 'imaginary clocks' we compare between can't give us the same 'time'. Doesn't matter from where you measure, although if you measure from a center, it's no longer empty, sort of, so then we would have to add whatever mass that is to our consideration.Gravitational field is not proportional to time dilation or length contraction, though. Time dilation and length contraction always involves comparing the point of view of two observers, so it involves comparing their two reference frames, including their relative motions and the difference in the gravitational field between them.So two observers at rest WRT each other inside the spherical shell both measure the same, zero net gravitational force and they agree on measurements of clocks and meter sticks. If one observer is inside and one is distant and both are at rest WRT the spherical shell, they they DO observe length contraction/time dilation, since any communication they have with each other has to pass through the gravitational field outside the shell. They observe this despite the fact that each locally measures no gravitational force.

How can length contraction and time dilation not have a proportionality WRT gravity. They are caused by either the gravitational field or the relativistic momentum of a mass.

We rely too much on observer perspectives. The universe doesn't need observers for the laws of physics to apply.

The other problem is the complexity of interactions. I know the Higgs field should have an interaction with gravity but this can't be possible if the graviton is massless and travels at c. If the graviton has mass it no longer travels at c and gravity falls apart. Also if it has mass it isn't going to pass through matter. This tends to suggest another as yet unknown particle that provides an indirect mechanism. I can't find a way for this to happen. So to answer a previous question, yes, gravity SUCKS!

And if you use 'light clocks' you will see that time dilations and Lorentz contractions aren't solely connected to inertia, or gravity. It's a result of the fact that 'c' is a constant invariant factor, belonging to all 'inertial frames of reference', aka uniform motions. It's always 'c', doesn't matter how fast your uniform speed (geodesic/velocity) is relative some other reference frame. So describing it as a proportionality to gravity solely becomes a tough proposition.=What I personally think is that there must be a connection to 'c' for gravity too though. And 'c' is a description of displacements over time, but, as locally defined. If you want to be strict we define a proper mass from uniform motion too btw. Accelerations plays havoc with your scale, as you weight yourself, so we need to include proper mass there too. And then we have transformations and 'energy' which are the ones making it make sense, although not locally measurable, except as gravity/inertia under accelerations.So not only 'c', but 'local'. The last, to me, means that we need to wonder what 'motion' is, and how we define a clock, and so also a 'distance'. All of those are local definitions made from a uniform motion.And then there is relativistic mass, which is the sort of mass you can't measure locally in a uniform motion, or acceleration, but becomes very tangible in any collision, expressed in kinetic energy. And that is a added problem as it neither is measurable from the vacuum, nor locally in your uniformly moving, or accelerating, rocket. What you can measure locally is a blue/redshift, and a gravity/inertia under a acceleration but it's not proportional to your relativistic mass, as you easily can see thinking of accelerating at one uniform gravity, considering the kinetic energy expressed in a collision, at different times. And if in a uniform motion this too will be absent, locally.Einstein gave us one description, QM gives us one more, with Higgs defining inertia under accelerations. None of them seems wrong, but none of them seems to tell the whole story either. Not to forget, we have classical physics too, as Newtons and Maxwell's that works really nice under normal circumstances. Einstein said himself that it was Maxwell that gave him the idea of 'c', if I remember right.

Well, it's one of the hardest ideas to encompass in relativity. I like measurements, and using those you have no extra 'energy' stored locally, in a added uniform motion, also called relative motion. But we have measurably different velocities inside this universe.Neither will you measure the vacuum outside to contain more energy due to that added motion. But Einstein describes it in his stress energy tensor. In that gravity becomes a result of the geometry of SpaceTime, as I get it defined by mass energy and the geodesics something will take, 'time' is another parameter necessary, naturally, for it to exist. In that geodesics will describe the geometry. "Mass tells space-time how to curve, and space-time tells mass how to move.". How that is translated into a uniformly accelerating rocket, and its relativistic mass, aka kinetic energy, as measured from a collision is a trickier one, that I really would like to understand from measurements, aka experiments. I definitely have to agree with Pete in that 'relativistic mass' must exist though. I think you also might translate it into 'potential energy', well possibly? But I like measurements/experiments.=what you can define in any motion though is a changed relation between frames of reference. If you measure light from a sun, and then start to move towards it, you will find light to blue shift. But is that the same as a perfect vacuum? And how can I prove a perfect vacuum to change, using no suns, measurable radiation? Another sore point of such an idea is the question, if I now, by defining the vacuum as able to unmeasurably 'change' due to my motion, now won't have to present it (the vacuum) as a 'absolute frame of reference'?There are no absolute frames of reference in relativity, only locally definable constants, those proven to exist by anyone doing a (equivalent) local experiment, giving us our definition of 'repeatable experiments'.

My point is that there is a varying gradient through spacetime of both length contraction and time dilation. This would only be apparent if viewed from infinity where gravity has no influence. Since we can't do that experimentally we have to devise some means of theoretically assuming we are working from infinity. After all g is taken as negative and referenced from infinity. If all we do is chop the universe up into an infinite set of frames of reference that can only be viewed locally or transformed one at a time we are missing the bigger picture. To solve the Einstein field equations we have to think outside the box. The tools we are using haven't worked for a solution to gravitation for the last 100 years.

Quote from: jeffreyH on 28/01/2014 15:25:49My point is that there is a varying gradient through spacetime of both length contraction and time dilation. This would only be apparent if viewed from infinity where gravity has no influence. Since we can't do that experimentally we have to devise some means of theoretically assuming we are working from infinity. After all g is taken as negative and referenced from infinity. If all we do is chop the universe up into an infinite set of frames of reference that can only be viewed locally or transformed one at a time we are missing the bigger picture. To solve the Einstein field equations we have to think outside the box. The tools we are using haven't worked for a solution to gravitation for the last 100 years.Sure they have. We can use them to make lots of calculations, including correcting for gravitational time dilation in GPS. Obviously general relativity is incomplete since it doesn't work with quantum theory, but that doesn't mean it's wrong. It's a model that works where its supposed to work and will have limitations like any model. Saying we need to think outside the box is true (if thinking in the box worked, we'd already have a working theory of quantum gravity), but it doesn't tell us anything. If you want to say that the idea of an observer in GR is flawed, you need to come up with a replacement theory that makes new predictions and explains why GR works so very well for observers, because it does!

As an example of this thinking, if you are relating all your measurements of a wave function from a position halfway up the rising edge of a peak you don't see it in the same way as removing yourself and viewing from a distance. Your calculations are much less complex when you can see the whole thing.

Quote from: jeffreyH on 29/01/2014 09:56:43As an example of this thinking, if you are relating all your measurements of a wave function from a position halfway up the rising edge of a peak you don't see it in the same way as removing yourself and viewing from a distance. Your calculations are much less complex when you can see the whole thing.The problem is that all measurements are local. You can't "see the whole thing." Rather, you see whatever information reaches your local position. If you're at the right place at the right time you can measure the entire thing as a sum of local measurements.

That article looks very poorly written and the results look very poorly quantified. It would take a lot of effort to dig into the meat of the paper, since it provides no descriptions of what the expected diffraction pattern would be using a standard model and what the difference in the measured model is. The difference looks to be within experimental error (indeed, the author notes that the measured values are within the "uncertainty relation" for the fringe visibility/which way information). His claims seem to be that there are some qualitative differences and that he suspects with better equipment he could prove quantum mechanics wrong. Given that it is relatively straightforward to compute the diffraction patterns in this case and then to compare them quantitatively to experiments, I'd relegate this to a well-intentioned paper by someone who doesn't understand the physics or math involved. And given that he's trying to overturn 200 years of wave theory of light, he needs more than well-intentioned hand-waving to do so.By the way, this experiment is classical. Although light is photons, these effects can be understood and modeled by classical waves and Maxwell's equations, so finding a violation with theoretical predictions would invalidate Maxwell's equations.