But the two stars are actually 5ly apart.
The ship would know that from its charts.
Quote from: Norm38 on 08/01/2017 03:37 pmBut the two stars are actually 5ly apart.Norm, I think statements like these are where you're going wrong. There are no "actual" lengths in relativity. There are only lengths measured in various reference frames. The same with time intervals.QuoteThe ship would know that from its charts.No, the ship would only know that in another frame of reference the two stars are 5 ly apart. There is nothing special about the terrestrial frame of reference.Similarly, there is no "actual" order of events. There are only order of events observed form various reference frames which, as others are telling you, do not necessarily agree. As long as signal speeds are restricted to light speed and lower this doesn't create any causality problems. But if we postulate faster than light signal speeds causality violations occur.
The "proper length" or distance is the distance between the two stars in the frame in which the observer is at rest relative to those stars. This distance is 5ly. All other frames moving relative to this frame will show a shorter distance between them. It is special because it is the "only" frame in which the stars have 5ly between them. The ship is not at rest relative to these stars, and the pilot should be smart enough to know that what he measures as the distance between those two stars is not the "proper distance".
In your previous post you said;"The very foundation of relativity is that all inertial reference frames are equivalent. "but the first postulate of relativity actually says;"The laws of physics are the same in all inertial frames of reference."These two statements are NOT the same thing.
Your statement is an "assumption" of what you think it means, but I gave examples on page 6 of this thread, showing that we CAN have different inertial reference frames with different scaling parameters and still, "The laws of physics are the same in all inertial frames of reference.", regardless of how that frame is scaled.
So you see, there is a hidden assumption that if the laws of physics are the same, then the inertial reference frames are "equal", but my example proves that this is not necessarily true. We can have inertial reference frames that are not equal and have different scaling and still the laws of physics do not change.
Quote from: WarpTech on 08/01/2017 06:08 pmIn your previous post you said;"The very foundation of relativity is that all inertial reference frames are equivalent. "but the first postulate of relativity actually says;"The laws of physics are the same in all inertial frames of reference."These two statements are NOT the same thing.The second statement is slightly more formal, but they do not mean anything different.
Quote from: WarpTech on 08/01/2017 06:08 pmYour statement is an "assumption" of what you think it means, but I gave examples on page 6 of this thread, showing that we CAN have different inertial reference frames with different scaling parameters and still, "The laws of physics are the same in all inertial frames of reference.", regardless of how that frame is scaled.If you are saying that there is a magic absolute "scale value" that is different in different inertial reference frames, you are breaking the first postulate. (Remember we are talking about flat spacetime where K is a constant.)
Quote from: WarpTech on 08/01/2017 06:08 pmSo you see, there is a hidden assumption that if the laws of physics are the same, then the inertial reference frames are "equal", but my example proves that this is not necessarily true. We can have inertial reference frames that are not equal and have different scaling and still the laws of physics do not change.That is not a hidden assumption, but the explicit statement.You did not prove what you said because either:- K is the same in all inertial reference frames in flat spacetime (the "different scaling" is not true)- K differs between inertial reference frames, which is a change in the laws of physics. (Besides the fact that you only showed that the value for force is unchanged, plenty of other values would be changed such as velocity and acceleration.)
However, gravitational fields fill all space-time within our galaxy and motion relative to a gravitational field can be detected. I've said before and I'll say it again, our "local baseline" is the gravitational field of the Earth/Sun solar system.
Regarding the 1st postulate; using the dimensional conversions,Mass M = M0*K3/2Length L = L0/√KTime T = T0*√KCalculate how Forces depend on K. Simple;Force = (Mass)*(Length)/(Time)2 = (M0*K3/2)*(L0/√K)/(T0*√K)2 So => M*L/T2 = M0*L0/T02In other words, the forces we measure in experiments are completely independent of the local value of K. So all inertial reference frames will experience the same forces and have the same results to ALL experiments that verify SR and GR.
The relative value of K can ONLY be measured by a distant observer, comparing two different regions of space-time.
Quote from: WarpTech on 08/01/2017 10:00 pmHowever, gravitational fields fill all space-time within our galaxy and motion relative to a gravitational field can be detected. I've said before and I'll say it again, our "local baseline" is the gravitational field of the Earth/Sun solar system.This highlights the main problem in this discussion, you simply insist on talking about curved spacetime, when the discussion is about essentially flat spacetime. We are not talking about local reference frames in general relativity where there is a measurable difference in gravitational potential between the 2 locations.I did read your previous post (relevant part quoted below).You showed that force would be unchanged, but ignored that velocity and acceleration would clearly be changed, therefore your logic is simply wrong.Quote from: WarpTech on 07/27/2017 11:28 pmRegarding the 1st postulate; using the dimensional conversions,Mass M = M0*K3/2Length L = L0/√KTime T = T0*√KCalculate how Forces depend on K. Simple;Force = (Mass)*(Length)/(Time)2 = (M0*K3/2)*(L0/√K)/(T0*√K)2 So => M*L/T2 = M0*L0/T02In other words, the forces we measure in experiments are completely independent of the local value of K. So all inertial reference frames will experience the same forces and have the same results to ALL experiments that verify SR and GR. Quote from: WarpTech on 08/01/2017 10:00 pmThe relative value of K can ONLY be measured by a distant observer, comparing two different regions of space-time.I think you are confused here, relative values don't need to be measured by a distant observer, as a practical example, we can measure the difference between the "Earth Ground" frame and the "GPS satellite" frame using the change in clock speed. The "distant observer" is used as a way to define an absolute scale.
Quote from: Norm38 on 08/01/2017 04:55 pmTime dilation is not an illusion, that is the only thing that is real. The gamma factor of relativistic travel is real and that is what separates the reference frames from each other. The Solar system and surrounding stars are moving at about 0.00075c. That is what separates our reference frame from that of a 0.6c ship.Moving at 0.00075c or 0.6c relative to what? You seem to be assuming that there is some special reference frame, which is in contradiction with relativity.
Time dilation is not an illusion, that is the only thing that is real. The gamma factor of relativistic travel is real and that is what separates the reference frames from each other. The Solar system and surrounding stars are moving at about 0.00075c. That is what separates our reference frame from that of a 0.6c ship.
This highlights the main problem in this discussion, you simply insist on talking about curved spacetime, when the discussion is about essentially flat spacetime. We are not talking about local reference frames in general relativity where there is a measurable difference in gravitational potential between the 2 locations.
True, the "distant observer" sets a baseline where there are no gravitational fields, where the gravitational potential is "0" and as such, the frame where gravitational potential is null is a preferred frame in this model.
There is no way to measure the value of K locally.
Quote from: as58 on 08/01/2017 05:00 pmQuote from: Norm38 on 08/01/2017 04:55 pmTime dilation is not an illusion, that is the only thing that is real. The gamma factor of relativistic travel is real and that is what separates the reference frames from each other. The Solar system and surrounding stars are moving at about 0.00075c. That is what separates our reference frame from that of a 0.6c ship.Moving at 0.00075c or 0.6c relative to what? You seem to be assuming that there is some special reference frame, which is in contradiction with relativity.Something that I've been wondering about is CMBR dipole anisotropy. Our galaxy is moving at about 622 km/s compared to the CMB. Since the CMB can be measured anywhere in the universe, doesn't that create a prefered frame?
Something that I've been wondering about is CMBR dipole anisotropy. Our galaxy is moving at about 622 km/s compared to the CMB. Since the CMB can be measured anywhere in the universe, doesn't that create a prefered frame?
...Quote from: WarpTech on 08/01/2017 11:05 pmThere is no way to measure the value of K locally.You left off the word "relative" this time, so I think we can agree. (Tentative on me doing more research, but this is unimportant anyway, because we are only talking about flat spacetime.)Now try answering this question:In flat spacetime, there are 2 objects with a velocity relative to each other of 0.6c. Is K the same for the rest frame of each of these objects?If not, how would the distant observer (who can basically be right next to the objects because flat space time) tell what the difference is?
Now try answering this question:In flat spacetime, there are 2 objects with a velocity relative to each other of 0.6c. Is K the same for the rest frame of each of these objects?If not, how would the distant observer (who can basically be right next to the objects because flat space time) tell what the difference is?
Quote from: RonM on 08/01/2017 11:26 pmSomething that I've been wondering about is CMBR dipole anisotropy. Our galaxy is moving at about 622 km/s compared to the CMB. Since the CMB can be measured anywhere in the universe, doesn't that create a prefered frame?I want to talk about this too. I'm a bit afraid that in doing so it will get tangled in debates on basic relativity. Im not using "basic relativity" in a derogatory sense because I know I haven't personally mastered it. I would prefer to stick to the textbook pronouncements and not try to convince anyone who disputes them. There will always be someone in the conversation better qualified to do that.This "CMB rest frame as special" is IMO the best solution so far. I have pasted it into the OP so that it doesn't get drowned in the basic relativity discussion.I also made a point that I think this is equivalent to defining "simultaneous" as an isosurface though space-time where the CMB is a specific temperature. (you can also find this pasted into the OP).The thing I wanted to add was, the CMB rest frame choice isn't merely nice. I think it is special because I think it almost rules out any other choice.. if you are going to chose some frame and label it special it pretty much has to be this one.Why? because you are either choosing the ONLY definition of "instantaneous" where you are travelling between points of the universe that have the same temperature and entropy, and look pretty similar, or you are choosing ANY OTHER one where travel in one specific arbitrary direction takes you to a younger, hotter universe, and the other direction takes you to a colder one, even though the universe does not look hotter or colder in either of those directions. Only one choice of reference frame is nice, all the others are "yuck". Apart from being "yuck", there are probably horrible exploits you could implement if you could slide freely between entire observable universes at different states of entropy. IMO that makes one choice head and shoulders above an other possible one.Bear in mind this does not override any laws of relativity. Like entropy itself, it is not really required by any of the other laws, which are all reversible. Yet we still live in a universe where change in entropy is perhaps the most important feature.
...As of yet, there is no evidence that motion relative to the CMBR has any effect at all. However, I don't think it's been tested yet either.
In reality, however, not all directions in the sky appear to have the same CMB brightness. The earth is moving with respect to the matter that last emitted the CMB, and therefore the CMB spectrum looks bluest (and, by Wien's law, therefore hottest) in that direction and reddest (and coolest) opposite to that direction....If the dipole contribution due to Earth's motion is now subtracted out, the sky looks like the figure at the left.
Most likely it is still wrong since I don't know of any scientists who espouse the hypothesis. But that doesn't matter as long as it serves as a good backstop for sci-fi that makes a good-faith effort to incorporate known natural law as well as logic.
Have any of the well-known authors of hard sci-fi (like, say, Greg Egan) built worlds based on the hypothesis yet?
Quote from: meberbs on 08/01/2017 11:27 pmNow try answering this question:In flat spacetime, there are 2 objects with a velocity relative to each other of 0.6c. Is K the same for the rest frame of each of these objects?If not, how would the distant observer (who can basically be right next to the objects because flat space time) tell what the difference is? There's time's arrow, and then there's mass. Which object accelerated, which one didn't? Which is more massive? If a tiny ship and an entire galaxy are both observed, it's pretty easy to tell which one is moving. Especially if the galaxy isn't moving at sublight relative to neighboring galaxies.Reference frames can appear exactly the same at steady state, but they have histories and memories and are not the same. One is real, one is transitory.
In both cases, it would be impossible to tell from just the objects. In order to do anything, each object would need to be radiating a known frequency and wavelength, such as the Hydrogen absorption spectrum, or other known spectral sources. As well has having a well defined intensity amplitude, (a standard candle) so that they can be compared with enough detail to determine what red/blue shift is due to K and what red/blue shift is due to relative motion.
In this model, the fact that the speed of light is a constant to all inertial observers is a "result" of the fact that rulers and clocks are renormalized when the value of K in the local environment changes. If it were not for this quantum mechanical process, the value of c would not be constant to all local observers.
To have length contraction and time dilation requires more than just a vacuum. It requires quantum vacuum fluctuations and power dissipation. Neither GR or SR require this, although it is there if you formulate the correct problem and know where to look. That is why these are classical theories, where mine is a quantum theory. In Relativity, all vacuum is the same. In QED, all vacuums are not the same.
Flat space-time: Start with the massless particles, (Bosons), EM field photons, Strong field gluons and fill the entire universe with their minimum energy state, the Zero-point fields (ZPF)'s. Add to this massive particles, (Fermions) the Dirac field, the electron family, the quark family, etc.. and their ZPF's.Add to this EM, weak and strong forces acting on the particles and particles acting on the fields.Add to this the CMB radiation field and all the long range fields that span the universe.
As of yet, there is no evidence that motion relative to the CMBR has any effect at all. However, I don't think it's been tested yet either.
What magic keeps track of the "history" of any given object? What is the measurable effect that this has?"if the galaxy isn't moving at sublight" You apparently have not understood a single word of anything you have read about relativity if you think an entire galaxy moving at FTL makes any sense.
You asked how a distant observer could tell two reference frames apart. A history of observation is one way. I said two reference frames at steady state could be mathematically equivalent. But a ship that just accelerated and a galaxy that didn't are different. They can be distinguished.
Next is mass (or energy state). An observer sees a small ship and an entire galaxy. Yes it is nonsensical for the ship to be stationary and the entire galaxy to be moving at 0.6c. (Especially when the galaxy isn't moving at that speed relative to other galaxies). The object with the largest mass and lowest energy state is the rest frame.
In completely flat empty nothing then yes an observer can't tell if it's the ship or the galaxy moving. But our universe is not flat and empty. It has structure. Structure on massive scales.
An observer's state of motion cannot affect an observed object, but it can affect the observer's observations of the object.