Halc

Both had the comma, and yes, I missed it. Thanks for the clarity. I do read screens without glasses since they don't help at all.

I know know the topic is old enough to have given birth by now, but the acceleration is +g downward or -g upward. The way you've both said it says the accelerates upward acceleration is negative, which would be true of something repelled by Earth.

There are no superluminal jets. The effect in question was simple motion more or less towards Earth, and it only requires a velocity in our direction of > 0.5c. So let's say a space ship begins a journey to Earth from a point 3 LY away, at a constant speed of 0.6c. At time 0 (years), it departs, to arrive at time 5, but we don't see that departure for 3 years since it takes 3 years for light to get to us from that far away. So at time 3 we observe the departure from 3 LY away and at time 5 it gets here. So to us it looks like the ship took only two years to go 3 LY, superluminal, right? No, since time for light travel was not taken into account in that calculation. Ditto for the jets, which only appear fast due to this sort of Doppler compression.

Motion is a change in coordinate spatial location over time. 'Motion through time' isn't really a defined thing. Under a 3D model, a thing evolves in place as time progresses. In a 4D spacetime model, a thing traces a worldline through spacetime and is everywhere present on that line. There is no motion, no progression in such an abstraction. Both of these are worded like speed is some kind of absolute property. Remember to word it as "relative to a given frame, the closer an objects velocity is to the speed of light, the coordinate time for that object relative to said frame, slows down". So say relative to the frame of a muon, Earth is moving at near light speed and clocks on Earth run much slower than the clock on the muon. Yes, it has a clock. Note that I also removed the word 'perception' from your sentence since the time dilation is a coordinate effect, an abstract computed thing, not actually perceived by anything anywhere (per the first postulate of SR). Your 'theory' violates this explicitly and contradicts empirical evidence. Perception is always of proper time, not of coordinate time. Yea, why not the opposite? Or rather, why do you think not the opposite? I referenced the muon just above. Not sure what is meant by this. Proper time (that which clocks measure) is a measure of a time-like interval. It isn't something that slows, not for anybody. This is a popular concept, but is wrong. It essentially says "If [something impossible], I can conclude anything I like" since it's not even wrong, sort of like asking how long Earth's orbit would take to change if the sun suddenly ceased to exist. Actually, I did it just now, and you're right, you get younger. I have photographic evidence of it. Anyway, I'm back so I could post this. I do balk at the term 'pilot', which makes it sound like I needed an aircraft or something.

That's a classical radius, and I said that size was a classical concept. Swonsont beat me to it. To quote the site: "The classical electron radius is a combination of fundamental physical quantities that define a length scale for problems involving an electron interacting with electromagnetic radiation. It links the classical electrostatic self-interaction energy of a homogeneous charge distribution to the electron's relativistic mass-energy." I don't entirely get that, and I certainly don't know how that sort of thing can be measured to 11 significant digits. Nevertheless, defining this size is 'useful', so there it is. To also quote the same site and show what I was talking about: "According to modern understanding, the electron is a point particle with a point charge and no spatial extent."

A solid is definitely classical. But what I should have said is that size doesn't apply to fundamental things like an electron. All such things are quantum, but technically a horse is a quantum thing as well, so not all quantum things are without meaningful size.

'Singularity' doesn't mean 'object of size zero'. It means conditions under which the equations no longer produce meaningful results. It means a different theory (or different coordinates, or something else) is needed to describe what goes on under said condition. You note this below. As for zero size object, size is a classical concept and doesn't really apply to quantum things. The uncertainty principle loosely says you cannot know both momentum and position at the same time. Neither references a size. A quantum description probably doesn't work either since it cannot describe the spacetime curvature. A unified theory would really help.

First of all, I support blueshift exactly due to it being the highest frequency primary color. Secondly, assignment of the primaries is not a matter of arbitrary choice. It is a human thing, the three colors to which the human eye cones are optimally tuned. A different creature would assign totally different colors. Are our eyes truly tuned more to violet than blue? If so, then Young has a point. We have three primary colors (RGB) and three pigments (CMY), the colors of the ink in the cartridges, each of which absorbs one of the three primaries and reflects the other two. Squirrels can actually see yellow and would immediately be able to distinguish a banana from an object painted with yellow pigment, which is no more a color on the spectrum than is magenta which fits nowhere on the rainbow. Magenta is simply the absence of human green.

There's always an object stationary in almost any arbitrary frame choice, even if it's just a muon or neutrino somewhere. Observer, no, but observers in relativity don't actually observe anything except instruments, which can be done by anybody regardless of motion. For instance, a fast approaching clock is observed to run fast despite actually running slow in the observer's frame. His role is to run the the computations and provide a name for the frame, neither task requiring any actual observation. As for my assertion that say length contraction is not a physical effect, there are examples that can demonstrate it so. Rotation is absolute so via rotation, coordinate effects have physical consequences. A spinning ring will fit through an identical (*) ring not spinning. That's real contraction and not just coordinate like the barn pole thing is. Another example is a circular train track packed with cars. As they pick up speed, more cars will fit in the same track who's circumference is unchanged, despite the fact that relative to any one train car, the track just below it is shorter and one would think that relative to the cars, fewer would fit in the same contracted circle. Not so. * Unless really thin (2D), a spinning 3D object cannot be identical to a non-spinning one.

But the perspective of Earth was not mentioned. Just "co-ordinate mass of the Falcon 2 is approaching infinte at 99.99%c", which is true of me now relative to some frame. No fancy ship needed. But sure, if that speed is relative to some other object, then relative to the ship, it is the moving object (Earth??) that gains coordinate mass. Gian also implies that acceleration and/or energy is required for something to have a large coordinate speed. This isn't true at all since several examples have been given of Earth moving at nearly c. It's a coordinate effect. Nothing is physically different in such a frame.

Pretty much that answer, yes, except I don't remember Earth being involved in the question. I had just chosen a frame where the ship (and Earth too) were moving at .9999c But yes, in the frame where the Falcon is at rest, its coordinate mass and mass are identical, by definition.

Tidal disruption (the breakup of moons that fall below the Roche limit) is essentially Newtonian physics and has been fairly well understood since the 19th century. It has little if anything to do with gravitational waves and more with physical stress on orbiting objects. Earth for instance puts out a total energy of about 200 watts in the form of gravitational waves. It has plenty of tidal gradient to say destroy the moon if it ever gets close enough (it will be destroyed before this happens), but that 200 watts will not register on any detector we make. Yes, an orbiting GW detector will presumably be more sensitive than LIGO, but would lack the redundancy of the multiple GW detectors on Earth unless they orbit several of them. Not sure how much redundancy is needed in space where trucks driving nearby are not going to trigger false positives.

OK, it does seem to be a measurement topic, and not one of expressability or predictability Measurement of planets is hard due to the long delay between where it is and where you see it. The OP didn't seem to reference prediction Your OP seemed to have little to do with entropy. Your card shuffle example was one of a chaotic function, but the deck seems no more entropic before or after the shuffle, as opposed to if you play 52 pickup. This seem to have nothing to do with relativity theory. Choice of coordinate system was necessary even in Newton's physics. The sun's frame is an accelerating one, more complicated. I chose an inertial frame, but I didn't compute many numbers in it. Just >180 and 'faces the other way'. This is true, and you need two of them, not just one. Given distant stars not in the system, we have that reference. The OP said to ignore the gravitational influence of the rest of the galaxy, but that doesn't mean we don't have external references. Without it, picking a stable reference is possible (since rotation is absolute), but not as easy. But I chose the CoM as the reference. That's not an absolute reference, sure, but the relationships between the planets can be derived from each planet's coordinate relative to that CoM. Measuring it all is another problem since there's nowhere to be that sees where everything is at a given time since the distances are so large.

Well, you posted this in relativity, so it needs to be stated that you seem to be referencing states at times relative to some inertial frame, say the frame of the center of mass of the collection of objects, which is stable in isolation. The question seems to be how to express the states 1,2,3 Sure, in state 2 the Earth object has rotated just over 180 degrees and is facing the other way. It has also moved around the solar system just like all the other objects. I referenced the solar system center of mass, so given that reference, each of the objects has a position relative to that at each of the times 1,2,3. It's a stable point of reference, so nobody is worrying about saying where Earth is relative to Jupiter since both have moved. Measuring it is another thing, but measuring doesn't seem to be your question.

This two-year old topic started with the below comment. I've not read almost any of it, but I see a lot of word salad that seems unrelated to this original question. 1) No rigid object can instantly change its velocity without breaking, per Bell's spaceship scenario. You can accelerate it over time (finite proper acceleration), and how much time that takes depends on what clock is used to do it. There are limits. I worked out the minimum time it takes to move a 100 LY rigid train a distance of one light day, being stopped at beginning and end of trip. It takes almost 2 months and cannot be done faster without violating rigidity. It cannot be done at all without applying force to all parts of the object instead of say pulling it with an engine up front. Now regarding this latest post, forgive me if I am unaware of any context that might help make sense of any of it. How can a velocity be treated as a distance? This seems meaningless. How does a simultaneity or a nonsimultaneity have a size? Two events not simultaneous in some frame would have a time difference in time, but that difference would be a time, not a speed. You are seemingly comparing a time to a speed, which is total nonsense. How is any of the posts (in any of 2024) relevant to the topic? Is this just one of those blogs left open to keep the forum from filling up with dozens of crazy topics from one user?