A big pie, rotating in the sky, should have apparently shorter circumference than a non-rotating one, and both with the same radii.
I can’t swallow this. Not because it is weird, but because it is inconsistent.
There is no inconsistency. In one case you are measuring the circumference with moving rulers, while in the other case you are measuring the circumference with stationary rulers. It’s not inconsistent for these two different measurements to give different results.
No. I am measuring from here, from the centre with some measuring device.
First I measure stationary pie, then I measure the rotating one. Those red-white stripes are either constant, either they shrink. If they are shrinking, they should multiply as well. If they are not shrinking, what happened with Mr. Lorentz’s contraction?
If you measure a wheel with a ruler, and the wheel is moving relative to the ruler, then your measurement assumes that both ends of a piece of the wheel line up with both ends of a piece of the ruler at the same time. Whether these events happen at the same time, and therefore whether this is a measurement of the wheel, are different depending on the frame of reference.
Special Relativity + some basic mechanics leads to an apparent contradiction in the expected measurements, which is only resolved by introducing a curved space(time). So this would be a failure of self-consistency: the same theory leads to two different results for the same experiment.
However, the two measurements of ostensibly the same thing are done by different observers, so there is no requirement that they should agree. Introducing curved space for the rotating disk shows how to calculate distances consistently.
The problem is that it’s inconsistent with solid-body physics?
Solid-body physics is an approximation. This isn’t hard to show. Just bend something.
Consider the model of masses connected by springs. This is consistent with special relativity, and can be used to model solid-body physics. In fact, it’s a more accurate model of reality than solid-body physics.
Just to clarify, is the spinning pie a set of particles in the same relative position as with a still pie, but rotating around the origin? Is it a set of masses connected by springs that has reached equilibrium (none of the springs are stretching or compressing) and the whole system is spinning? Is the pie a solid body?
What exactly we’re looking at depends on which of the first two you picked. If you picked the third, it is contradictory with special relativity, but there’s a lot more evidence for special relativity than there is for the existence of a solid body. Granted, a sufficiently rigid body will still be inconsistent with special relativity, but all that means is that there’s a maximum possible rigidity. Large objects are held together by photons, so we wouldn’t expect sound to travel through them faster than light.
The spinning set of particles is a toroidal with let say 1 million light years across—the big R. and with the small r of just 1 centimetre. It is painted red and white, differently each metre.
The whole composition starts to slowly rotate on the signal from the centre. And slowly, very slowly accelerate to reach the speed of 0.1 c in a several million years.
Now, do we see any Lorentzian contraction due to the SR, or not due to the GR?
(Small rockets powered by radioactive decay are more than enough to compensate for the acceleration and for the centrifugal force. Both incredibly small. This is the reason why we have choose such a big scale.)
I’m going to assume mass is small enough not to take GR into effect.
From the point of view of a particle on the toroid, the band it’s in will extend to about 1.005 meters long. Due to Lorentz contraction, from the point of reference of someone in the center, it will appear one meter long.
The question is ONLY for the central observer. At first he sees 1 m long stripes, but when the whole thing reaches the speed of 0.1 c, how long is each stripe?
I just want to clarify. I’m assuming the particles are not connected, or are elastic enough that stretching them by a factor of 1.005 isn’t a huge deal. If you tried that with solid glass, it would probably shatter.
I wasn’t interpreting “sees” literally, but it wouldn’t make much of a difference. Since the observer is in the center of the circle, the light lag is the same everywhere. The only difference is that the circles bordering the bands will look slightly slanted, and the colors will be slightly blue-shifted.
Place red and white equilength rulers on the edge of the cylinder. The rotating cylinder will have more and shorther rulers. Thus the photos are not the same. Even better have the cylinder slowly pulse in different colors. The edges will pulse more slowly thus not being in synch with the center.
Related phenomenon is that moving ladders fit into garages that stationary ones would not.
Place red and white equilength rulers on the edge of the cylinder. The rotating cylinder will have more and shorther rulers.
They will multiply as the orbital speed increases? Say that Arab numerals are written on the rulers. Say that they are 77 at the beginning. Will this system know when to engage the number 78?
Or will there be two 57 at first? Or how is it going to be?
I was thinking of already spun cylinder and then adding the sticks by accelerating them to place.
If you had the same sticks already in place the stick would feel a stretch. If they resist this stretch they will pull apart so there will be bigger gaps between them. For separate measuring sticks they have no tensile strenght in the gaps between them. However if you had a measuring rope with continous tensile strenght and at a beginning / end point where the start would be fixed but new rope could freely be pulled from the end point you would see the numbers increase (much like waist measurements when getting fatter). However the purpoted cylinder has maximum tensile strenght anywhere continously. Thus that strenght would actually work against the rotating force making it resist rotation. a non-rigid body will rupture and start to look like a star.
So no there would not be duplicate sticks but yes the rope would know to engage number 78.
If you would fill up a rotating cylinder with sticks and spin it down the stick would press against each other crushing to a smaller lenght. A measuring rope with a small pull to accept loose rope would reel in. A non-rigid body slowing down would spit-out material in bursts that might come resemble volcanoes.
Saying that a moving ladder “fits” means that the start of the ladder is in the garage at the same time that the end of the ladder is. If the ladder is moving and contracted because of relativity, these two events are not simultaneous in all reference frames. Thus, you cannot definitely say that the moving ladder fits—whether it fits depends on your reference frame. (In another reference frame you would see the ladder longer than the garage, but you would also see the start of the ladder pass out of the garage before the end of the ladder passes into it.)
Why have that definition of “fit”? I could eqaully well say that fitting means that there is a reference frame that has a time where the ladder is completely inside.
If you had the carage loop back so that the end would be glued to the start you could still spin the ladder inside it. From the point of the ladder it would appear to need to pass the garage multiple times to oene fit ladder lenght but from the outside it would appear as if the ladder fits within one loop completely. With either perspective the one garage space enough to contain the ladder without collisions. In this way it most definetly fits. Usually garages are thought to be space-limited but not time limited. Thus the eating of the time-dimension is a perfectly valid way of staying within the spatial limits.
edit: actually there is a godo reazson to priviledge the rest frame oft he garage as the one that count as ragardst to fitting as then all of the fitting happens within its space and time.
Why have that definition of “fit”? I could eqaully well say that fitting means that there is a reference frame that has a time where the ladder is completely inside.
In that case, the ladder fits.
From the point of the ladder
Each rung of the ladder has a distinct reference frame. “From the point of the ladder” is meaningless.
If the ladder point of view is ildefined so is the garage point of view as the front and back of the garage have distinct reference frames. Any inertial reference frame is equally good. The ladder is not accelerating thus inertial. In the sense that we can talk of any frame as more than a single event or world line the ladder frame is perfectly good.
In the normal example, where the ladder is straight and moving forward, it has only one reference frame. Strictly speaking, each rung has a different reference frame, but they differ only by translation.
From what I understand, you modified it to a circular ladder spinning in a circular garage. In this case, each rung is moving in a different direction, and therefore at a different velocity. Thus, each rung has its own reference frame.
ah, I meant to glue the end and start together without curved shape/motion. But I guess that is physically unrealisable and potentially more distracting than explanatory.
Actually that’s not a big deal. Technically you need general relativity to do that, but it’s just a quotient space on special relativity. In any case, it works out exactly the same as an infinite series of ladders and garages.
There is one thing you have to be careful about. From the rest frame, the universe could be described as repeating itself every, say, ten feet. But from the point of view of the ladder, it’s repeating itself every five feet and 8.8 nanoseconds. That is, if you move five feet, you’ll be in the same place, but your clock will be off by 8.8 nanoseconds.
Actually from the point of view of the ladder the universe still repeats at every ten feet. It is just that from it’s point of view it takes the space of two carages at any one instant.Both the garage and ladder are in a state of rest and show equally good times. Yes they read different but doesn’t mean they are in error.
I am not sure whether it would see other instances of itself. I only spesified a spatial gluing and not that the garage be split into timeslices. I guess that the change of the point of view has changed some of that gluing to be from future to past. For if the ladder would be too long the frontend would not crash to the same ladder time backend but to a future one. (ignoring the problem of how you would try to slide the ladder into too small a hole in the first place)
Actually from the point of view of the ladder the universe still repeats at every ten feet.
No, it does not. I think I messed up before and it’s actually 20 feet and 8.8 nanoseconds. From the the point of view of the garage, the coordinates (0 ft, 0 ns) and (10 ft, 0 ns) correspond to the same event. From the point of view of the ladder, the coordinates became (0 ft, 0 ns) and (20 ft, 8.8 ns). They still have to be the same event.
The universe is definitely repeating itself to be off by a certain time, and the distance it is off by is not ten feet.
The ladder sees the carage length contract. That is less than 10 feet. The ladder doesn’t see itself contract that puts the limit on the repeating of the universe.
Are you sure the ladder point equivalences are not (0 ft, 0ns) and (20 ft, −8.8ns)?
If the rotating pie is a pie that when nonrotating had the same radius as the other one, when it rotates it has a slightly larger radius (and circumference) because of centrifugal forces. This effect completely dominates over any relativistic one.
The centrifugal force can be arbitrary small. Say that we have only the outer rim of the pie, but as large as a galaxy. The centrifugal force at the half of speed of light is just negligible. Far less than all the everyday centrifugal forces we deal with.
Now say, that the rim has a zero around velocity at first and we are watching it from the centrer. Gradually, say in a million years time, it accelerates to a relativistic speed. The forces associated are a millionth of Newton per kilogram of mass. No big deal.
The problem is only this—where’s the Lorentz contraction?
As long as we have only one spaceship orbiting the Galaxy, we can imagine this Lorentzian shrinking. In the case of that many, that they are all around, we can’t.
If you have a large number of spaceships, each will notice the spaceship in front of it getting closer, and the circle of spaceships forming into an ellipse.
At least, that’s assuming the spaceships have some kind of tachyon sensor to see where all the other ships are from the point of reference of the ship looking, or something like that. If they’re using light to tell where all of the other ships are, then there’s a few optical effects that will appear.
The question is what the stationary observer from the centre sees? When the galactic carousel goes around him. With the speed even quite moderate, for the observer has precise instruments to measure the Lorentzian contraction, if there is any.
At first, there is none, because the carousel isn’t moving. But slowly, in many million years when it accelerate to say 0.1 c, what does the central observes sees? Contraction or no contraction?
They mustn’t. All should be smooth just like those Einstein’s train. No resulting breaking force is postulated.
The force is due to chemical bonds. They pull particles back together as their distance increases. These chemical bonds are an example of electromagnetism, which is governed by Maxwell’s laws, which are conserved by Lorentz transformation.
Granted, whether a field is electric or magnetic depends on your point of reference. A still electron only produces an electric field, but a moving one produces a magnetic field as well. But if you perform the appropriate transformations, you will find that looking at a system that obeys Maxwell’s laws from a different point of reference will result in a system that obeys Maxwell’s laws.
In fact, Lorentz contraction was conjectured based on Maxwell’s laws before there was any experimental evidence of it. Both of those occurred before Einstein formulated special relativity.
But everything boils down to the “a microscope which enlarges the angles”
Lorentz transformation does not preserve angles Euclidean distance or angles. It preserves something called proper distance.
How it would look like?
This is what Lorentz transformation on 1+1-dimensional spacetime looks like: https://en.wikipedia.org/wiki/Lorentz_transformation#mediaviewer/File:Lorentz_transform_of_world_line.gif. There’s one dimension of space, and one of time. Each dot on the image represents an event, with a position and a time. Their movement corresponds to the changing point of reference of the observer. The slope of the diagonal lines is the speed of light, which is preserved under Lorentz transformation.
Here’s my question for you: with all of the effort put into researching special relativity, if Lorentz transformation did not preserve the laws of physics, don’t you think someone would have noticed?
The problem is only this—where’s the Lorentz contraction?
Each piece of the ring is longer as measured by an inertial observer comoving with it than as measured by a stationary one (i.e. one comoving with the centre of the ring). But note that there’s no inertial observer that’s comoving with all pieces of the ring at the same time, and if you add the length of each piece as measured by an observer comoving with it what you’re measuring is not a closed curve, it’s a helix in spacetime. (I will draw a diagram when I have time if I remember to.)
During the million years of small acceleration, the torus will have to stretch (i.e. each atom’s distance from its neighbours, as measured in its own instantaneous inertial frame will increase) and/or break.
Specifying that you do it very slowly doesn’t change anything—suppose you and I are holding the two ends of a rope on the Arctic Circle, and we go south to the Equator each along a meridian; in order for us to do that, the rope will have to stretch or break even if we walk one millimetre per century.
I don’t see any reason this very big torus should break.
Forces are really tiny, for R is 10^21 m and velocity is about 10^8 m/s. That gives you 10^-5 N per kg of centrifugal force. Which can be counterbalanced by a small (radioactive) rocket or something on every meter.
Almost any other relativistic device from literature would easily break long before this one.
Not every relativistic projectile will be broken. And every projectile is relativistic, more or less.
Trying to escape from the Ehrenfest’s paradox with saying—this starship breaks anyway—has a long tradition. Max Born invented that “exit”.
Even if one advocates the breaking down of any torus which is moving/rotating relative to a stationary observer, he must explain why it breaks. And to explain the asymmetry created with this breakdown. Which internal/external forces caused it?
Resolving MM paradox with the Relativity created another trouble. Back to the drawing board!
Pretending that all is well is a regrettable attitude.
Even if one advocates the breaking down of any torus which is moving/rotating relative to a stationary observer, he must explain why it breaks. And to explain the asymmetry created with this breakdown. Which internal/external forces caused it?
Each piece of the ring is longer as measured by an inertial observer comoving
We, at this problem, don’t care for a “comoving” inertial observer. We care for the stationary observer in the center, who first see stationary and then rotating torus, which should contract. But only in the direction of moving.
Both forces are of the same magnitude! That’s why we are waiting 10000000 years to get to a substantial speed.
If one is so afraid that forces even of that magnitude will somehow destroy the thing, one must dismiss all other experiments as well.
Ehrenfest was right, back in 1908. AFAIK he remained unconvinced by Einstein and others. It’s a real paradox. Maybe I like it that much, because I came to the same conclusion long ago, without even knowing for Ehrenfest.
The question of the OP was about contrarian views. I gave 10 (even though I have about 100 of them). The 10th was about Relativity and I don’t really expect someone would convert here. But it’s possible.
That’s why we are waiting 10000000 years to get to a substantial speed.
Yes, and over 10000000 the forces can build up. Consider army’s example of the stretching rope. Suppose I applied force to one end of a rope sufficient that over the course of 10000000 years it would double in length. You agree that the rope will either break or the bonds in the rope will prevent the rope from stretching?
The same thing happens with the rotation. As you rotate the object faster the bonds between the atoms are stretched by space dilation. This produces a restoring force which opposes the rotation. Either forces accelerating the rotation are sufficient to overcome this, which causes the bonds to break, or they aren’t in which case the object’s rotation speed will stop increasing.
No one’s saying that forces “just build up” by virtue of applying for a long time. Azathoth123 is saying that in this particular case, when these particular forces act for a long time they produce a gradually accumulating change (the rotation of the ring) and that as that change increases, so do its consequences.
Your rope is moving faster and faster, whether or not it goes all the way around the galaxy. The relations between different bits of the rope are pretty much exactly the setup for Bell’s spaceship paradox.
Yeah, but it’s a “paradox” only in the sense of being confusing and counterintuitive, not in the sense of having any actual inconsistency in it. The point is that this is a situation that’s already been analysed, and your analysis of it is wrong.
It wouldn’t be a problem, if it was just “paradox”, but unfortunately it’s real.
We can’t and therefore don’t measure the postulated Lorentz contraction. We have measured the relativistic time and mass dilatation or increase, we did. But there is NO experiment confirming the contraction of length.
To get direct verification of length contraction we’d need to take something big enough to measure and accelerate it to a substantial fraction of the speed of light. Taking the fact that we don’t have such direct verification as a problem with relativity is exactly like the creationist ploy of claiming that failure to (say) repeat the transition from water-dwelling to land-dwelling life in a lab is a problem with evolutionary biology.
We have. The packet of protons inside LHC, Geneva.
Packets all around the circular tube. Nobody says, they shrink. They say those packets don’t qualify for the contraction as they are “not rigid in Born’s sens” and therefore not shrinking.
If we can measure even a tinny mass gain, we could measure a tinny contraction.
If you read the whole article instead of quote-mining it for damning-looking sentences, you will see that that’s incorrect.
They modelled, performed experiments, and compared the results. That’s how science works. The fact that the article also mentions what happens in the models beyond the experimentally-accessible regime doesn’t change that.
Every rigid body is just a cloud of particles. If they are bonded together, they are bonded together with other particles like photons. Or gravity. Or strong nuclear force, as quarks in protons and neutrons.
Also the strong nuclear force is responsible for bounding atomic nucleus together. The force just doesn’t stop at the “edge of a proton”.
But why do you think they “must be bonded together” in the first place?
Hubble flow is at best a very noncentral example of travelling. Also, images aren’t supposed to show any contraction (see Terrell rotation), only the objects themselves.
(Why are you expecting apparent sizes to match real sizes in the first place? The Sun looks as small as the Moon as seen from Earth, do you think it actually is?)
Of all light rays entering your eye right now, the ones coming from parts of the object farther away from you departed earlier than the ones coming from parts closer to you. If the object moved between those two times, its image will be deformed in a way that, when combined with Lorentz contraction, foreshortening, etc., will make the object look the same size as if it was stationary but rotated. This is known as Terrell rotation and there are animated illustrations of it on the Web.
(BTW, galaxies are moving along the line of sight, so their Lorentz contraction would be along the line of sight too, and how would you expect to tell (say) a sphere from an oblate spheroid seen flat face-first?)
I agree that “Lorentz contraction” is a misleading name; it’s just a geometrical effect akin to the fact that a slab is thicker if you transverse it at an angle than if you transverse it perpendicularly.
There’s a reason it’s called special relativity. It only works in special cases. Eucludian geometry and Newtonian mechanics are inconsistent, btw. Special relativity solves these inconsistencies in the special contexts where they originally came up (predicting the Lorentz contraction and time dilation which is experimentally observed). It wasn’t until the curved space of general relativity was discovered that we had a fully consistent model.
And yes, curved space of general relativity fully explains the rotating disc in a way that is self-consistent in in agreement with observed results (as proven by Gravity Probe B, among other things).
Special relativity is consistent. It just isn’t completely accurate.
It’s inconsistent with solid-body physics, but that’s due to the oversimplifications inherent in solid-body physics, not the ones inherent in special relativity.
Trying to fit solid-body physics into general relativity is even worse. With special relativity, it works fine as long as it doesn’t rotate or accelerate. Under general relativity, it can only exist on flat space-time, which basically means that nothing in the universe can have any mass whatsoever, including the object in question.
But then again, the question whether the study of flat spacetime using non-inertial reference frames counts as SR depends on what you mean by SR. If you mean the limit of GR as G approaches 0, then it totally does.
Right. Well I’d agree that special relativity is incoherent for accelerating rotating frames—it gives different experimental predictions depending on your choice of reference frame. It may be unusual to use accelerating reference frames, but they work just fine in classical physics. But they don’t in special relativity.
It’s not a very meaningful or contrarian statement though. Special relativity was known to be incoherent with regard to accelerating reference frames from day one. “Special” as in “special case”, which it is. I guess my objection here is thta the OP listed it as a contrarian viewpoint, but as far as I can tell it is the standard view taught in Physics 103.
It may be unusual to use accelerating reference frames, but they work just fine in classical physics.
No they don’t. From an accelerating reference frame, an object with no force on it will accelerate. You can only get it to work if you add a fictitious force.
I don’t think it’s accurate to call it incoherent for accelerating reference frames. If you try to alter the coordinate system so that something that was accelerating is at rest, and you try to predict what happens with the normal laws of physics, you’ll get the wrong answer. But it never says you should get the right answer. There’s symmetries in the laws of physics that cause them to be preserved by Lorentz transformations. Since a transformation can be found to make an arbitrary object be at rest at the origin and in a given orientation, it’s often useful to use the transformation so that you can do the math with the object being at rest. Special relativity simply does not have such a symmetry to allow an accelerating object to be changed to an object at rest.
The fact that you can’t use arbitrary “reference frames” doesn’t mean that special relativity only works for a special case any more than using the (x,t) |-> (-t,x) transformation on Newtonian physics not working means that Newtonian physics only works in special cases and is incoherent.
The reason special relativity is a special case is that it only applies to flat spacetime, when no mass is involved.
Yes.
A big pie, rotating in the sky, should have apparently shorter circumference than a non-rotating one, and both with the same radii.
I can’t swallow this. Not because it is weird, but because it is inconsistent.
There is no inconsistency. In one case you are measuring the circumference with moving rulers, while in the other case you are measuring the circumference with stationary rulers. It’s not inconsistent for these two different measurements to give different results.
No. I am measuring from here, from the centre with some measuring device.
First I measure stationary pie, then I measure the rotating one. Those red-white stripes are either constant, either they shrink. If they are shrinking, they should multiply as well. If they are not shrinking, what happened with Mr. Lorentz’s contraction?
If you measure a wheel with a ruler, and the wheel is moving relative to the ruler, then your measurement assumes that both ends of a piece of the wheel line up with both ends of a piece of the ruler at the same time. Whether these events happen at the same time, and therefore whether this is a measurement of the wheel, are different depending on the frame of reference.
Why is it inconsistent?
Special Relativity + some basic mechanics leads to an apparent contradiction in the expected measurements, which is only resolved by introducing a curved space(time). So this would be a failure of self-consistency: the same theory leads to two different results for the same experiment.
However, the two measurements of ostensibly the same thing are done by different observers, so there is no requirement that they should agree. Introducing curved space for the rotating disk shows how to calculate distances consistently.
The problem is that it’s inconsistent with solid-body physics?
Solid-body physics is an approximation. This isn’t hard to show. Just bend something.
Consider the model of masses connected by springs. This is consistent with special relativity, and can be used to model solid-body physics. In fact, it’s a more accurate model of reality than solid-body physics.
No, that’s not the issue. The problem is that no flat-space configuration works.
The spacetime itself is flat (if the mass of the pie is negligible), but the spacelike slices are curved because you’re slicing it in a weird way.
I have two photos of two different pies, one of rotating one and one of not rotating. Photos are indistinguishable, I can’t tell which is which.
On the other hand, both pies have one-to-one correspondence with photos an one should be slightly deformed on the edge.
Even if it is, on the photo can’t be. The photo is perfectly Euclidean. I have measured no Lorentz contraction.
In other news, the earth is really flat because photographs of the earth are flat.
Just to clarify, is the spinning pie a set of particles in the same relative position as with a still pie, but rotating around the origin? Is it a set of masses connected by springs that has reached equilibrium (none of the springs are stretching or compressing) and the whole system is spinning? Is the pie a solid body?
What exactly we’re looking at depends on which of the first two you picked. If you picked the third, it is contradictory with special relativity, but there’s a lot more evidence for special relativity than there is for the existence of a solid body. Granted, a sufficiently rigid body will still be inconsistent with special relativity, but all that means is that there’s a maximum possible rigidity. Large objects are held together by photons, so we wouldn’t expect sound to travel through them faster than light.
The spinning set of particles is a toroidal with let say 1 million light years across—the big R. and with the small r of just 1 centimetre. It is painted red and white, differently each metre.
The whole composition starts to slowly rotate on the signal from the centre. And slowly, very slowly accelerate to reach the speed of 0.1 c in a several million years.
Now, do we see any Lorentzian contraction due to the SR, or not due to the GR?
(Small rockets powered by radioactive decay are more than enough to compensate for the acceleration and for the centrifugal force. Both incredibly small. This is the reason why we have choose such a big scale.)
I’m going to assume mass is small enough not to take GR into effect.
From the point of view of a particle on the toroid, the band it’s in will extend to about 1.005 meters long. Due to Lorentz contraction, from the point of reference of someone in the center, it will appear one meter long.
The question is ONLY for the central observer. At first he sees 1 m long stripes, but when the whole thing reaches the speed of 0.1 c, how long is each stripe?
One meter.
I just want to clarify. I’m assuming the particles are not connected, or are elastic enough that stretching them by a factor of 1.005 isn’t a huge deal. If you tried that with solid glass, it would probably shatter.
Come to think of it, this looks like a more complicated form of Bell’s spaceship paradox.
I think you’re right, but you’re interpreting “sees” literally I’m not 100% sure of that, because of light aberration (the Terrell-Penrose effect).
I wasn’t interpreting “sees” literally, but it wouldn’t make much of a difference. Since the observer is in the center of the circle, the light lag is the same everywhere. The only difference is that the circles bordering the bands will look slightly slanted, and the colors will be slightly blue-shifted.
Place red and white equilength rulers on the edge of the cylinder. The rotating cylinder will have more and shorther rulers. Thus the photos are not the same. Even better have the cylinder slowly pulse in different colors. The edges will pulse more slowly thus not being in synch with the center.
Related phenomenon is that moving ladders fit into garages that stationary ones would not.
They will multiply as the orbital speed increases? Say that Arab numerals are written on the rulers. Say that they are 77 at the beginning. Will this system know when to engage the number 78?
Or will there be two 57 at first? Or how is it going to be?
I was thinking of already spun cylinder and then adding the sticks by accelerating them to place.
If you had the same sticks already in place the stick would feel a stretch. If they resist this stretch they will pull apart so there will be bigger gaps between them. For separate measuring sticks they have no tensile strenght in the gaps between them. However if you had a measuring rope with continous tensile strenght and at a beginning / end point where the start would be fixed but new rope could freely be pulled from the end point you would see the numbers increase (much like waist measurements when getting fatter). However the purpoted cylinder has maximum tensile strenght anywhere continously. Thus that strenght would actually work against the rotating force making it resist rotation. a non-rigid body will rupture and start to look like a star.
So no there would not be duplicate sticks but yes the rope would know to engage number 78.
If you would fill up a rotating cylinder with sticks and spin it down the stick would press against each other crushing to a smaller lenght. A measuring rope with a small pull to accept loose rope would reel in. A non-rigid body slowing down would spit-out material in bursts that might come resemble volcanoes.
Saying that a moving ladder “fits” means that the start of the ladder is in the garage at the same time that the end of the ladder is. If the ladder is moving and contracted because of relativity, these two events are not simultaneous in all reference frames. Thus, you cannot definitely say that the moving ladder fits—whether it fits depends on your reference frame. (In another reference frame you would see the ladder longer than the garage, but you would also see the start of the ladder pass out of the garage before the end of the ladder passes into it.)
Why have that definition of “fit”? I could eqaully well say that fitting means that there is a reference frame that has a time where the ladder is completely inside.
If you had the carage loop back so that the end would be glued to the start you could still spin the ladder inside it. From the point of the ladder it would appear to need to pass the garage multiple times to oene fit ladder lenght but from the outside it would appear as if the ladder fits within one loop completely. With either perspective the one garage space enough to contain the ladder without collisions. In this way it most definetly fits. Usually garages are thought to be space-limited but not time limited. Thus the eating of the time-dimension is a perfectly valid way of staying within the spatial limits.
edit: actually there is a godo reazson to priviledge the rest frame oft he garage as the one that count as ragardst to fitting as then all of the fitting happens within its space and time.
In that case, the ladder fits.
Each rung of the ladder has a distinct reference frame. “From the point of the ladder” is meaningless.
If the ladder point of view is ildefined so is the garage point of view as the front and back of the garage have distinct reference frames. Any inertial reference frame is equally good. The ladder is not accelerating thus inertial. In the sense that we can talk of any frame as more than a single event or world line the ladder frame is perfectly good.
In the normal example, where the ladder is straight and moving forward, it has only one reference frame. Strictly speaking, each rung has a different reference frame, but they differ only by translation.
From what I understand, you modified it to a circular ladder spinning in a circular garage. In this case, each rung is moving in a different direction, and therefore at a different velocity. Thus, each rung has its own reference frame.
ah, I meant to glue the end and start together without curved shape/motion. But I guess that is physically unrealisable and potentially more distracting than explanatory.
Actually that’s not a big deal. Technically you need general relativity to do that, but it’s just a quotient space on special relativity. In any case, it works out exactly the same as an infinite series of ladders and garages.
There is one thing you have to be careful about. From the rest frame, the universe could be described as repeating itself every, say, ten feet. But from the point of view of the ladder, it’s repeating itself every five feet and 8.8 nanoseconds. That is, if you move five feet, you’ll be in the same place, but your clock will be off by 8.8 nanoseconds.
Actually from the point of view of the ladder the universe still repeats at every ten feet. It is just that from it’s point of view it takes the space of two carages at any one instant.Both the garage and ladder are in a state of rest and show equally good times. Yes they read different but doesn’t mean they are in error.
I am not sure whether it would see other instances of itself. I only spesified a spatial gluing and not that the garage be split into timeslices. I guess that the change of the point of view has changed some of that gluing to be from future to past. For if the ladder would be too long the frontend would not crash to the same ladder time backend but to a future one. (ignoring the problem of how you would try to slide the ladder into too small a hole in the first place)
No, it does not. I think I messed up before and it’s actually 20 feet and 8.8 nanoseconds. From the the point of view of the garage, the coordinates (0 ft, 0 ns) and (10 ft, 0 ns) correspond to the same event. From the point of view of the ladder, the coordinates became (0 ft, 0 ns) and (20 ft, 8.8 ns). They still have to be the same event.
The universe is definitely repeating itself to be off by a certain time, and the distance it is off by is not ten feet.
The ladder sees the carage length contract. That is less than 10 feet. The ladder doesn’t see itself contract that puts the limit on the repeating of the universe.
Are you sure the ladder point equivalences are not (0 ft, 0ns) and (20 ft, −8.8ns)?
It depends on which direction it’s moving. I didn’t bother to check the sign.
Thinking about it now, if it’s going in the positive direction, then it should be (20 ft, −8.8ns). You are correct.
If the rotating pie is a pie that when nonrotating had the same radius as the other one, when it rotates it has a slightly larger radius (and circumference) because of centrifugal forces. This effect completely dominates over any relativistic one.
The centrifugal force can be arbitrary small. Say that we have only the outer rim of the pie, but as large as a galaxy. The centrifugal force at the half of speed of light is just negligible. Far less than all the everyday centrifugal forces we deal with.
Now say, that the rim has a zero around velocity at first and we are watching it from the centrer. Gradually, say in a million years time, it accelerates to a relativistic speed. The forces associated are a millionth of Newton per kilogram of mass. No big deal.
The problem is only this—where’s the Lorentz contraction?
As long as we have only one spaceship orbiting the Galaxy, we can imagine this Lorentzian shrinking. In the case of that many, that they are all around, we can’t.
If you have a large number of spaceships, each will notice the spaceship in front of it getting closer, and the circle of spaceships forming into an ellipse.
At least, that’s assuming the spaceships have some kind of tachyon sensor to see where all the other ships are from the point of reference of the ship looking, or something like that. If they’re using light to tell where all of the other ships are, then there’s a few optical effects that will appear.
The question is what the stationary observer from the centre sees? When the galactic carousel goes around him. With the speed even quite moderate, for the observer has precise instruments to measure the Lorentzian contraction, if there is any.
At first, there is none, because the carousel isn’t moving. But slowly, in many million years when it accelerate to say 0.1 c, what does the central observes sees? Contraction or no contraction?
He will see each spaceship contract. The distance between the centers of the spaceships will remain the same.
But no, those ships are just like those French TGV’s. A whole composition of cars and you can’t say where one ends and another begins.
It’s like a snake, eating its tail!
Then they stretch. Or break.
Or they stay the same but the radius of the train as measured by the observer in the centre will shrink.
They mustn’t. All should be smooth just like those Einstein’s train. No resulting breaking force is postulated.
But everything boils down to the “a microscope which enlarges the angles”
How do you then see two perpendicular intersecting lines under that microscope?
Can’t be.
This Lorentz contraction has the same fundamental problem. How it would look like?
The force is due to chemical bonds. They pull particles back together as their distance increases. These chemical bonds are an example of electromagnetism, which is governed by Maxwell’s laws, which are conserved by Lorentz transformation.
Granted, whether a field is electric or magnetic depends on your point of reference. A still electron only produces an electric field, but a moving one produces a magnetic field as well. But if you perform the appropriate transformations, you will find that looking at a system that obeys Maxwell’s laws from a different point of reference will result in a system that obeys Maxwell’s laws.
In fact, Lorentz contraction was conjectured based on Maxwell’s laws before there was any experimental evidence of it. Both of those occurred before Einstein formulated special relativity.
Lorentz transformation does not preserve angles Euclidean distance or angles. It preserves something called proper distance.
This is what Lorentz transformation on 1+1-dimensional spacetime looks like: https://en.wikipedia.org/wiki/Lorentz_transformation#mediaviewer/File:Lorentz_transform_of_world_line.gif. There’s one dimension of space, and one of time. Each dot on the image represents an event, with a position and a time. Their movement corresponds to the changing point of reference of the observer. The slope of the diagonal lines is the speed of light, which is preserved under Lorentz transformation.
Here’s my question for you: with all of the effort put into researching special relativity, if Lorentz transformation did not preserve the laws of physics, don’t you think someone would have noticed?
Then how are you accelerating them up to c/2?
With a tiny force of 1 micro Newton per kilogram of mass over several million years.
This was the acceleration force.
The centrifugal force is much less.
This is the force that will serve as the breaking force.
Each piece of the ring is longer as measured by an inertial observer comoving with it than as measured by a stationary one (i.e. one comoving with the centre of the ring). But note that there’s no inertial observer that’s comoving with all pieces of the ring at the same time, and if you add the length of each piece as measured by an observer comoving with it what you’re measuring is not a closed curve, it’s a helix in spacetime. (I will draw a diagram when I have time if I remember to.)
The inertial observer in the centre of the carousel measures those torus segments when they are stationary.
Then, after a million years of a small acceleration of the torus and NOT the central observer, the observer should see segments contracted.
Right?
During the million years of small acceleration, the torus will have to stretch (i.e. each atom’s distance from its neighbours, as measured in its own instantaneous inertial frame will increase) and/or break.
Specifying that you do it very slowly doesn’t change anything—suppose you and I are holding the two ends of a rope on the Arctic Circle, and we go south to the Equator each along a meridian; in order for us to do that, the rope will have to stretch or break even if we walk one millimetre per century.
I don’t see any reason this very big torus should break.
Forces are really tiny, for R is 10^21 m and velocity is about 10^8 m/s. That gives you 10^-5 N per kg of centrifugal force. Which can be counterbalanced by a small (radioactive) rocket or something on every meter.
Almost any other relativistic device from literature would easily break long before this one.
If breaking was a problem.
Can you see why the rope in my example would break or stretch, even if we’re moving it very very slowly?
Your example isn’t relevant for this discussion.
Why not?
Look!
Not every relativistic projectile will be broken. And every projectile is relativistic, more or less.
Trying to escape from the Ehrenfest’s paradox with saying—this starship breaks anyway—has a long tradition. Max Born invented that “exit”.
Even if one advocates the breaking down of any torus which is moving/rotating relative to a stationary observer, he must explain why it breaks. And to explain the asymmetry created with this breakdown. Which internal/external forces caused it?
Resolving MM paradox with the Relativity created another trouble. Back to the drawing board!
Pretending that all is well is a regrettable attitude.
Why wouldn’t that also apply to my rope example?
We, at this problem, don’t care for a “comoving” inertial observer. We care for the stationary observer in the center, who first see stationary and then rotating torus, which should contract. But only in the direction of moving.
It’s not the centrifugal force that’s the problem. It’s the force you are using to get the ring to start rotating.
Both forces are of the same magnitude! That’s why we are waiting 10000000 years to get to a substantial speed.
If one is so afraid that forces even of that magnitude will somehow destroy the thing, one must dismiss all other experiments as well.
Ehrenfest was right, back in 1908. AFAIK he remained unconvinced by Einstein and others. It’s a real paradox. Maybe I like it that much, because I came to the same conclusion long ago, without even knowing for Ehrenfest.
The question of the OP was about contrarian views. I gave 10 (even though I have about 100 of them). The 10th was about Relativity and I don’t really expect someone would convert here. But it’s possible.
Yes, and over 10000000 the forces can build up. Consider army’s example of the stretching rope. Suppose I applied force to one end of a rope sufficient that over the course of 10000000 years it would double in length. You agree that the rope will either break or the bonds in the rope will prevent the rope from stretching?
The same thing happens with the rotation. As you rotate the object faster the bonds between the atoms are stretched by space dilation. This produces a restoring force which opposes the rotation. Either forces accelerating the rotation are sufficient to overcome this, which causes the bonds to break, or they aren’t in which case the object’s rotation speed will stop increasing.
(or stretch)
In the case of the ring there’s another possibility.
Irrelevant. How many tiny forces are inside a street car? They don’t just “build up”.
Nonsense.
No one’s saying that forces “just build up” by virtue of applying for a long time. Azathoth123 is saying that in this particular case, when these particular forces act for a long time they produce a gradually accumulating change (the rotation of the ring) and that as that change increases, so do its consequences.
I understand. But imagine, that only 1 m of rope is accelerated this way. No “forces buildup” will happen.
As will not happen if we have rope around the galaxy.
Your rope is moving faster and faster, whether or not it goes all the way around the galaxy. The relations between different bits of the rope are pretty much exactly the setup for Bell’s spaceship paradox.
And? The Relativity isn’t coherent, that’s the whole point.
Transition from one, to another paradox doesn’t save the day.
Yeah, but it’s a “paradox” only in the sense of being confusing and counterintuitive, not in the sense of having any actual inconsistency in it. The point is that this is a situation that’s already been analysed, and your analysis of it is wrong.
It wouldn’t be a problem, if it was just “paradox”, but unfortunately it’s real.
We can’t and therefore don’t measure the postulated Lorentz contraction. We have measured the relativistic time and mass dilatation or increase, we did. But there is NO experiment confirming the contraction of length.
To get direct verification of length contraction we’d need to take something big enough to measure and accelerate it to a substantial fraction of the speed of light. Taking the fact that we don’t have such direct verification as a problem with relativity is exactly like the creationist ploy of claiming that failure to (say) repeat the transition from water-dwelling to land-dwelling life in a lab is a problem with evolutionary biology.
We have. The packet of protons inside LHC, Geneva.
Packets all around the circular tube. Nobody says, they shrink. They say those packets don’t qualify for the contraction as they are “not rigid in Born’s sens” and therefore not shrinking.
If we can measure even a tinny mass gain, we could measure a tinny contraction.
Had there been any.
Funny you should mention that.
See? It’s only calculation based on Relativity, not actual experimental data.
If you read the whole article instead of quote-mining it for damning-looking sentences, you will see that that’s incorrect.
They modelled, performed experiments, and compared the results. That’s how science works. The fact that the article also mentions what happens in the models beyond the experimentally-accessible regime doesn’t change that.
A bunch of particles not bound to each other by anything is not rigid in any reasonable sense I can think of, so what’s your point?
Every rigid body is just a cloud of particles. If they are bonded together, they are bonded together with other particles like photons. Or gravity. Or strong nuclear force, as quarks in protons and neutrons.
Also the strong nuclear force is responsible for bounding atomic nucleus together. The force just doesn’t stop at the “edge of a proton”.
But why do you think they “must be bonded together” in the first place?
https://en.wikipedia.org/wiki/Length_contraction#Experimental_verifications
The link you gave does not talk about the direct observation of the Lorentz contraction. Rather of “explanations”.
Fast traveling galaxies, of which all the sky is full, DO NOT show any contraction. That would qualify as a direct observation.
Hubble flow is at best a very noncentral example of travelling. Also, images aren’t supposed to show any contraction (see Terrell rotation), only the objects themselves.
If images aren’t supposed to show any contraction, then measurements aren’t supposed to detect any contraction.
My point exactly.
Are you saying, that there in an invisible contraction?
(Why are you expecting apparent sizes to match real sizes in the first place? The Sun looks as small as the Moon as seen from Earth, do you think it actually is?)
Of all light rays entering your eye right now, the ones coming from parts of the object farther away from you departed earlier than the ones coming from parts closer to you. If the object moved between those two times, its image will be deformed in a way that, when combined with Lorentz contraction, foreshortening, etc., will make the object look the same size as if it was stationary but rotated. This is known as Terrell rotation and there are animated illustrations of it on the Web.
(BTW, galaxies are moving along the line of sight, so their Lorentz contraction would be along the line of sight too, and how would you expect to tell (say) a sphere from an oblate spheroid seen flat face-first?)
I agree that “Lorentz contraction” is a misleading name; it’s just a geometrical effect akin to the fact that a slab is thicker if you transverse it at an angle than if you transverse it perpendicularly.
Yes. Rotated rope looks shorter. Problem remains.
We see the close and the far edge of many of them. Still, the pancake apparently isn’t neither squeezed neither rotated.
What problem?
There’s a reason it’s called special relativity. It only works in special cases. Eucludian geometry and Newtonian mechanics are inconsistent, btw. Special relativity solves these inconsistencies in the special contexts where they originally came up (predicting the Lorentz contraction and time dilation which is experimentally observed). It wasn’t until the curved space of general relativity was discovered that we had a fully consistent model.
And yes, curved space of general relativity fully explains the rotating disc in a way that is self-consistent in in agreement with observed results (as proven by Gravity Probe B, among other things).
Special relativity is consistent. It just isn’t completely accurate.
It’s inconsistent with solid-body physics, but that’s due to the oversimplifications inherent in solid-body physics, not the ones inherent in special relativity.
Trying to fit solid-body physics into general relativity is even worse. With special relativity, it works fine as long as it doesn’t rotate or accelerate. Under general relativity, it can only exist on flat space-time, which basically means that nothing in the universe can have any mass whatsoever, including the object in question.
Twin paradox.
What about the twin paradox?
Is it any Lorentz contraction visible in the case of around the galaxy rim?
Are all the Lorentzian shrinks just cancelled out?
I’d really like to know that.
You need GR if you want to treat talk about the rotating reference frame of the disk. Otherwise SR is fine.
“claim[ing] that special relativity can’t handle acceleration at all … is like saying that Cartesian coordinates can’t handle circles”
See http://math.ucr.edu/home/baez/physics/Relativity/SR/acceleration.html
But then again, the question whether the study of flat spacetime using non-inertial reference frames counts as SR depends on what you mean by SR. If you mean the limit of GR as G approaches 0, then it totally does.
You don’t need GR for a rotating disk; you only need GR when there is gravity.
Rotation drags spacetime.
Only if the rotating object is sufficiently massive.
Only if the rotating object has any mass at all.
For a rotating object of sufficiently small mass, the mass can be ignored, and reasonably accurate results can be found with special relativity.
I don’t disagree. This discussion was philosophical in the pejorative sense, being about absolutely exact results, not reasonable approximations.
The OP was claiming that special relativity was incoherent, not just that it wasn’t absolutely exact.
If you want absolutely exact results, you’ll need a theory of everything. There are quantum effects messing with spacetime.
Right. Well I’d agree that special relativity is incoherent for accelerating rotating frames—it gives different experimental predictions depending on your choice of reference frame. It may be unusual to use accelerating reference frames, but they work just fine in classical physics. But they don’t in special relativity.
It’s not a very meaningful or contrarian statement though. Special relativity was known to be incoherent with regard to accelerating reference frames from day one. “Special” as in “special case”, which it is. I guess my objection here is thta the OP listed it as a contrarian viewpoint, but as far as I can tell it is the standard view taught in Physics 103.
No they don’t. From an accelerating reference frame, an object with no force on it will accelerate. You can only get it to work if you add a fictitious force.
I don’t think it’s accurate to call it incoherent for accelerating reference frames. If you try to alter the coordinate system so that something that was accelerating is at rest, and you try to predict what happens with the normal laws of physics, you’ll get the wrong answer. But it never says you should get the right answer. There’s symmetries in the laws of physics that cause them to be preserved by Lorentz transformations. Since a transformation can be found to make an arbitrary object be at rest at the origin and in a given orientation, it’s often useful to use the transformation so that you can do the math with the object being at rest. Special relativity simply does not have such a symmetry to allow an accelerating object to be changed to an object at rest.
The fact that you can’t use arbitrary “reference frames” doesn’t mean that special relativity only works for a special case any more than using the (x,t) |-> (-t,x) transformation on Newtonian physics not working means that Newtonian physics only works in special cases and is incoherent.
The reason special relativity is a special case is that it only applies to flat spacetime, when no mass is involved.