What is Reddit's opinion of Introduction to Special Relativity (Dover Books on Physics)?

From 3.5 billion Reddit comments

>What I struggle to understand is why. Since speed of light is the same for all frames, then if we know in advance that the ship will travel at steady speed, plus what that speed will be, then shouldn't we be able to time the difference between pulses of light flashed by a ship to communicate and use those to calculate away any relativistic distortions?

We can always calculate what a different observer will see. We can always adjust the rate at which we send some signal so that they will see them arrive at equal intervals as they change reference frames, but then we would see the signal change rate. An example would be communicating with a probe that's accelerating away from earth. It might be easier to transmit the signal on a changing frequency (from our perspective) so that the probe doesn't need to carry electronics that can properly detect longer-wavelength signals.

>Or even Lorentz transform them away?

I'm not sure what this means. The Lorentz transform is a mathematical construct we use to describe the universe. We can't use it to alter how the universe works.

>Also, if we assume that the ship had to accelerate at takeoff until it reached a steady speed then didn't it already break symmetry and therefore we can start to compare clocks?

Breaking the symmetry doesn't allow us to compare clocks by itself, it means there could exist a difference between them when we do compare them. Acceleration may be necessary for one observer to return home so that the clocks can be compared locally, but it's not necessary for the paradox to exist other than to cause observers to be in different frames. We can start the problem with the twins being the same age and one already moving, or with the three-person no-acceleration setup in the video, no one accelerates at all.

>Since the wording often says what each twin will view or see, it isn't clear if the twins' dual observations of both aging slower is merely a distorted perception from relativistic effects. If both were aging slower then they'd be the same age at each point of the journey.

Be careful to distinguish what the see and how their clocks are ticking relative to one another. As there is no absolute simultaneity, both clocks can be running slow relative to one another as long as the observers are in different reference frames. The twin on the return journey home will actually see the earth as moving in fast-forward, but this is a result of the Doppler effect. I think this is what you're getting at, but notice that while the relativistic Doppler effect shows us just what we would see, it includes time dilation as well. There is a difference between just what you see and how time is actually passing.

>I don't understand why we cannot use a constant like the speed of light to gauge the age differences.

I'm not quite sure what this means. The two observers are moving relative to one another but both measure the same beam of light as moving at the same speed. In order for them to make that measurement of light moving at the same speed, then they must disagree on how fast their clocks are ticking and how long their rulers are.

>Let's say that instead of human twins, we use cloned twins guaranteed to have the same lifespan if they were in the same frame of reference. Now we tweak the test by connecting each twin to a device that flashes a powerful beam of light when their telomeres reach a certain length or even if the twin dies of old age, and say both twins were already quite old when they began the test. Shouldn't the other twin be able to use that light to know that the other twin has in fact aged faster?

No, the signal from each twin announcing their death would reach the other after they had already died, assuming the setup is such that the twins have been moving at constant speed relative to one another the entire time.

Don't worry if this is hard to wrap your head around -- this stuff is really confusing! I think it would help you to back up a little bit and spend some time with the basics of special relativity before moving on to the twin paradox, as the twin paradox applies a lot of those basic concepts. Once you have those down, it will be much easier to work through the twin paradox. A book like this one will cover all that and more (and will do a much better job of explaining it than I have)!

>Their relative velocity is 0 to each other before they travel, by pure luck. Same reference frame.

Then in order to come together, one or both must accelerate. Acceleration is not relative: we can detect that we are doing it without reference to the outside universe. If one of the two accelerates, then they have broken the symmetry and there is no expectation they be the same age in any event.

If they both do, then there is no asymmetry and they will agree on being the same age. Each will receive news of the birth of the other after their own birth, then see the other age in fast-forward as they move together until they are the same age when they arrive together.

>Hmm, let's say the speed and distance is low enough that this is not an issue when the ships are passing by.

Then they will not have a significant disagreement. The doppler effect exists at all speeds, and if you're moving slowly then the system is well-approximated as being classical and any relativistic effects are going to be tiny.

>Hmm, I guess putting aside relativity, just by pure light delay, you would see me being born before you (as light takes time to travel), then as I get closer, light more rapidly hits you (or rather takes less time to, since rapid might not be the proper word here), making it seem as though I am suddenly aging faster. I guess this is what the Doppler effect you are talking about is, or well it seems that's what you mean.

That's correct. Be careful, though: the classical Doppler effect and the Relativistic Doppler effect will give quantitatively different answers. If you use a non-relativistic expression for the Doppler shift you will get the wrong answer.

>Even after taking into account light delays, time dilation still applies, it's unrelated.

Correct, but the light delays prevent us from breaking causality or even being able to compare our ages/states in real time. There's no absolute time, so as long as the delay exists there are no conflicts.

>What see is just instrument problems.

No, the maximum rate at which information can travel is why relativity exists! It's not some "instrument issue", the structure of the universe forbids it.

>So we get close enough that light speed and Doppler aren't a problem anymore, and we can actually observe the true state of each other (but we do not stop, we just pass each other by at the low speed we were travelling before).

I don't know what this means. The Doppler Effect is extremized as you move faster.

>Now here is the problem, the true state of you from my perspective should be younger than me, and the true state of me from your perspective should again be the same.

NO. Again, there's no way for us to have some magical "same initial state". You're imagining that we can somehow, outside of relativity, agree on an initial, objective "true" state. Such a thing does not exist. This is a weird concept, but it's how the universe works.

At this point, you need to slow down with all the words and thought experiments. Get a text on special relativity (this one or this one are both good). You've clearly put a lot of thought into this, but at this point you're just running yourself in circles shifting the problem from one place to another.