Strange

Which questions? You were given examples where spectra are used on Earth, on Mars, in space, etc. We also understand the mechanisms by which a prism separates the different frequencies present in the light. So there is no sensible reason to expect different results.

You can't have it both ways. You just said that the ladder is no longer there and the doors are closed for a long period of time. Therefore they will appear to be closed in both frame of reference. I can close the front and back door of my house simultaneously (e.g. with a bit of string tied to each) and walk back and forth between them to see they are both closed at the same time. Another frame of reference will see them both closed. But will disagree about the time at which they both closed. It doesn't matter how you arrange to communicate the instant of closing between the two doors: beams of light, rods, odd shaped extensions to the doors. That mechanism will be triggered at different times in each frame of reference. If, as in the ladder version, the doors close and open really quickly then there will be no "clap" in either frame. If there is a clap, then it will happen at different relative times in each frame of reference.

Which is pretty much the same thing. The colour will depend on the direction the light comes from. The light (directly) from the Sun will be white. The light scattered from other directions will depend on the colour of the sensors it has been reflected from. Obviously. But I have no idea what!

If they do, then they do in both frames of reference and the question then is: When do they touch? The instant at which they come together will be different for each frame of reference.

Exactly. Because there is nothing to scatter the light.

Or no one knows. Or cares.

You can only see light when it arrives at your eye. This will only be the case for rays that come directly from the sun to your eye. Therefore you will only see a small disk where rays come directly from the sun. Light arriving from the sun to other parts of the sky will be on a trajectory that does not intersect your eye, therefore you will not see the light from those rays. Unless they are scattered and arrive at your eye. As someone else said, how hard is this? Are you pretending to be dumb for entertainment purposes?

It is a bit pointless trying to ignore the explanation and then saying there is no explanation. The reason it is relevant is because you are using a mechanical structure to transfer information (the time at which the door becomes fully closed) from the two doors. This is no different from using flashes of light when the doors are closed. The flashes would be simultaneous in one frame of reference and not another. Your mechanical arrangement will not change that: neither frame of reference will see the rods/door-extensions/whatever meet but they will have different explanations for why not. In one case it will be because the doors closed at different times, in the other case it will be because the mechanical structure was distorted (that will be true in both cases, but is only important in one). Your new version of the experiment where you just close the two doors with no worry about the ladder passing through isn't really relevant because, obviously, if you keep the doors closed then at some point everyone will see them as closed. The measurement of simultaneity needs to be related to an event (e.g. the time at which the doors become fully closed). This event will happen at a different time in each frame. There is no way of communicating information instantly between the two doors; nor is there any way of communicating the information in such a way that the communication will take the same time in both frames of reference. Your "logical" conclusion is wrong. You just need to make the effort to understand why. As you are unwilling to do this, this thread is probably pointless. Also, as you are clearly trying to contradict relativity, I shall suggest it is moved to the speculations forum. Then, if you just continue with unsupported assertions, it will probably be closed.

If here were no scattering, then the sky would be black apart from the little bit where the sun was.

I think it would be a static snapshot - there are some videos that animate the ripples radiating away. That would be the time dimension. I don't know if there is also some distortion in the time dimension. You are right: it is just characteristic of waves. They all happen to be sine curves (or close approximations to sine). Good question ... Very good question ... We might need a Mordred to answer that!

I guess you can think of the vertical component of the wave representing the strain (stretching and compression) in that direction. It is hard to imagine how you would visualise the sideways strain at the same time.

Why would they increase in energy? And however much energy they had, they couldn't escape. It would just increase the mass of the black hole.

It is a valid argument. The theory is mathematically consistent therefore you can't produce inconsistent results. Relativity might be wrong (it isn't) but it would still be consistent. I will let someone else try and explain your errors.

exactly. But if the charges of the particle and anti-particle were not exactly equal (and opposite) then they would not cancel exactly. So there would be some charge left over. But as photons are neutral, the charges must be equal. #conservation-laws

Neither. They are alternating compression/stretching at right angles to the direction of travel:

They have opposite charge (electrons are negative, positrons have positive charge). Their spin will be opposite if they are created as a pair but are not otherwise related.

In the theory of relativity, it cannot happen in one frame of reference and not the other. Therefore the error is in your thought experiment. You have been given the probable reason. I don't know what else you want. Work out what will happen to those extra bits you have added to the doors when accelerated at the rates required by the thought experiment. (They will probably be destroyed.)

Ah, very good. Sounds more likely.

As far as we know, the inside of a black hole behaves just like the outside. The same laws of physics should apply. But we can never test this, so I suppose we don't really know. Not sure why you think the laws of physics don't apply/ It makes no difference if it is matter or radiation. It will all fall to the centre of the black hole. Radiation doesn't escape from a black hole. If you are thinking of Hawking radiation, that is created at the event horizon. The photons from Hawking radiation could, conceivably create particle-antiparticle pairs (https://en.wikipedia.org/wiki/Pair_production) but I don't know if they would have enough energy.

Maybe a ceiling fan that is battery operated? You can buy one on Amazon for a few dollars. You would need to know the power consumed by the motor and the energy capacity (mAh) of the battery. From that you can work out the lifetime of the battery (or, the size of battery needed for a given period of operation). There isn't really much more that can be said with this little detail.

So your doors open like a Delorean? Fair enough. (If a little impractical ) And instead of rods with the rod contact points at the ends, you have trapezoidal panels which swing with the doors? This doesn't really change anything. So, it is still exactly the same explanation as above. The panels will be compressed/deformed by the acceleration of the opening and closing and will never meet in either frame of reference. As that can't happen the theory doesn't have to explain it. What needs to be explained is where the error is in your scenarios. I am fairly sure it is because of rigidity. But let's see what Janus says as he always demonstrates a great insight into such problems.

Same here. I am baffled as to why anyone would believe in gods but equally baffled as to why anyone would care that other people do. I long ago gave up worrying about why people play golf.

But you are asking us to focus on your "second door system". You need to explain your diagrams for that (instead of assuming people don't understand the basic problem). The top diagram seems to be some sort of isometric projection with doors that are either open or closed but only seem to cover the top half of the opening. The bottom diagram shows some lines. I don't know which are supposed to be the doors, from which direction is is seen or which way they move. Even some simple annotations would help. But while you think about that: 1. Special relativity is internally consistent so, even if it were wrong, it is impossible for there to be a paradox of the sort you propose. (This is a mathematical proof so has nothing to do with evidence, tests, correctness, etc) 2. As a result, your conclusion that there is a paradox is mistaken. We all need to work together to understand where the error is in your thought experiment. 3. You cannot disprove a scientific theory with a thought experiment (if that is what you are trying to do). 4. Any communication between the doors at each end to test if they are both closed at the same time can only take place at the speed of light or less. That is why the rods will not meet in either frame of reference. The same sort of argument must apply to your second system. But as none of us (it seems) have understood it, it is hard to say more than that.

Im afraid I can’t make any sense of those drawings. Can you explain it?

Another good article on what colliding galaxy clusters tell us about dark matter and modified gravity theories: https://medium.com/starts-with-a-bang/the-bullet-cluster-proves-dark-matter-exists-but-not-for-the-reason-most-physicists-think-b6bc1320a21b