How does time work? Pt II Special Relativity.

How does science work? And what's all this about quantum mechanics?

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Arising_uk
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Re: How does time work? Pt II Special Relativity.

Post by Arising_uk »

HexHammer wrote:No, I'm right! I put myself in the place of ppl with low spatial navigation, when you have high spatial navigation, the problem is you already have foreknowledge of this, thus you will not see the teaching flaws.
So what are they?

The comic/cartoon form is just about the best pedagogy for teaching those with low everything - the CIA discovered this when they researched ways to get to the illiterate peasant.

However, you appear to ignore a couple if things, one, it's currently just a blog and I presume uwot will be using constructive feedback to produce his book, and two, the people likely to want to read such a subject are likely to not be those with 'low spatial navigation'(whatever that is supposed to mean?).
Belinda
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Re: How does time work? Pt II Special Relativity.

Post by Belinda »

uwot wrote:Horses for courses. I doubt there is any single explanation that will click for everyone. I'm sorry it doesn't work for either of you.
As far as I am concerned, physics is so very difficult that I cannot maintain my concentration for long even on the cartoons which you linked to.The problem is mine.
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HexHammer
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Re: How does time work? Pt II Special Relativity.

Post by HexHammer »

Arising_uk wrote:
HexHammer wrote:No, I'm right! I put myself in the place of ppl with low spatial navigation, when you have high spatial navigation, the problem is you already have foreknowledge of this, thus you will not see the teaching flaws.
So what are they?

The comic/cartoon form is just about the best pedagogy for teaching those with low everything - the CIA discovered this when they researched ways to get to the illiterate peasant.

However, you appear to ignore a couple if things, one, it's currently just a blog and I presume uwot will be using constructive feedback to produce his book, and two, the people likely to want to read such a subject are likely to not be those with 'low spatial navigation'(whatever that is supposed to mean?).
I have exceedingly low spatial navigation because of my massive ADHD, I had to search for a vid that in very very .........very simple terms explained this relativity which made me understand and comprehend it.

The relative motion of an object relative to self it will show that the ball bounces in a straight line up and down, but to an observer far away the motion will seem like zigzag, the zigzag should be shown in 1 big picture, instead of cutted into small frames, that will confuse the reader.

Science should be for all humans, not just the elite.
uwot
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Re: How does time work? Pt II Special Relativity.

Post by uwot »

Belinda wrote:As far as I am concerned, physics is so very difficult...
Well, there's different sides to physics.
1. The starting point is just looking at the world and seeing what happens, which on the everyday scale, we all do and is simple enough.
2. The hard part is finding a way to describe it mathematically, so that we can predict what will happen, and develop technology that will enable us to have some control over our environment. Isaac Newton wasn't the first person to see an apple falling, but he was the first to come up with an equation that described the relationship between an apple and the Earth in a mathematically rigorous way.
3. The third part is where the boundaries between physics and philosophy become blurred; it's the bit where you try and explain why things happen the way they do. Some physicists don't care, because to do part 2 successfully, it doesn't really matter.

Thanks to the hard work of generations of physicists, we have developed technology like the Hubble Space telescope and the Large Hadron Collider. Such marvels have given us a view of things that our ancestors could only dream of. So we can see and describe what actually happens in pretty good detail. To give you an analogy, fluid dynamics is the field of physics that deals with the flow of liquids; the mathematics is incredibly complicated, but you don't need to understand it to see that water goes down the plughole. All I'm trying to do is show the things that physicists have discovered, in a way that doesn't involve a ton of very difficult maths. A lot of what happens is so far removed from our everyday experience, that we don't have any familiarity with it; if you had never seen water going down the plughole, what sort of cartoon would adequately describe it? In a way, that's the problem I have.
uwot
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Re: How does time work? Pt II Special Relativity.

Post by uwot »

HexHammer wrote:The relative motion of an object relative to self it will show that the ball bounces in a straight line up and down, but to an observer far away the motion will seem like zigzag, the zigzag should be shown in 1 big picture, instead of cutted into small frames, that will confuse the reader.
That's a good idea. Thank you, HexHammer.
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Noax
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Re: How does time work? Pt II Special Relativity.

Post by Noax »

I am posting in this thread because of the subject. This is my attempt at demonstrating the twin-problem, without resorting to rockets, accelerated reference frames or other complications from general relativity.
The twin problem also known as the twin-paradox even though it is not a paradox.

There are three people Edgar, Oscar, and Irving. Each of them is at rest in his own inertial frame and does not accelerate for the duration of the exercise. Nobody has a rocket or propulsion of any kind. Each one has a clock that measures elapsed time for them. The clocks matter more than the people do, but I wanted to name them. In the frame of any person, the other two only move along a single axis (left,right) Nobody has a y (forward, backward) or z (up, down) component to their motion relative to another.

There are three events (points in spacetime) P, Q, R. Each person is present at two of the three events. P is where Edgar and Oscar meet. Q is where Oscar and Irving meet, and R is where Irving and Edgar meet.

P is the start point, at time zero for both Edgar and Oscar who are present at that event. Edgar is moving left of Oscar at .866c relative to Oscar and Oscar is moving right of Edgar at .866c relative to Edgar. At that velocity, there is a time/space dilation factor of 2, meaning the clock of either person runs at half speed in the frame of the other.

In Oscar's frame:
After 194 minutes, Oscar has gone nowhere, but his clock reads 194, and event Q happens, which is when Oscar and Irving meet. Irving at that time sets his clock to 194. Meanwhile, Edgar is 168 light minutes to the left of event Q, and his clock reads 97 at the same time as event Q since at the speed he's moving, his clock runs at half normal pace. If Oscar tries to read Edgar's clock from event Q, he might see a figure near 35 I think since the light reaching him now came from when the clock said that. That's the only figure with complicated math, and that one is unimportant.

In Edgar's frame:
After 388 minutes, Edgar has gone nowhere, but his clock reads 388, and event Q happens 336 light-minutes to the right, which is Oscar and Irving meeting. Oscar's clock is running at half-speed, so it reads only 194.

In Irving's frame:
Irving is moving at .866c to the left in Edgar's frame, so Edgar is moving .866c to the right in Irving's frame. Irving's clock reads 194 because he is just now at event Q syncing his clock to Oscar's. At event Q, Edgar's clock reads 679 minutes.
Note that simultaneous with the same event Q, Edgar's clock reads 97 in Oscar's frame, 388 in Edgar's frame, and 679 in Irving's frame. This is a classic illustration of the relativity of simultaneity that SR describes.

Still in Irving's frame, between events Q and R:
After 194 minutes, Irving has gone nowhere, but his clock reads 388, and event R happens, which is when Irving and Edgar meet. Edgar's gained 97 minutes since it runs at half the pace of Irving's clock, and now says 776 at event R.

Edgar's frame, between events Q and R:
Edgar's clock read 388 when Q happened, so it ticks off another 388 minutes while Irving does the return trip and Edgar still goes nowhere. At event R, Irving's clock reads 388, half the value of Edgar's clock, thus illustrating the twin-problem all without resorting to general relativity. Note that in both Oscar's and Irving's frames, Edgar's clock ran at half pace, not double-pace.

Think of Edgar, Oscar, and Irving as Earthbound, Outbound, and Inbound respectively. That's why those names were chosen. I picked 97 minutes for duration interval since 168/97 is handily close to the square root of 3 and made a lot of the figures work out to round numbers.


If anybody finds fault in the description above, please point it out.
uwot
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Re: How does time work? Pt II Special Relativity.

Post by uwot »

OK Noax, this is giving me a headache, but I'll give it a go.
Noax wrote:P is the start point, at time zero for both Edgar and Oscar who are present at that event. Edgar is moving left of Oscar at .866c relative to Oscar and Oscar is moving right of Edgar at .866c relative to Edgar. At that velocity, there is a time/space dilation factor of 2, meaning the clock of either person runs at half speed in the frame of the other.
So far so good.
Noax wrote:In Oscar's frame:
After 194 minutes, Oscar has gone nowhere, but his clock reads 194, and event Q happens, which is when Oscar and Irving meet. Irving at that time sets his clock to 194. Meanwhile, Edgar is 168 light minutes to the left of event Q, and his clock reads 97 at the same time as event Q since at the speed he's moving, his clock runs at half normal pace.
Well, if his clock reads 97, then it is Edgar that is moving.
Noax wrote:If Oscar tries to read Edgar's clock from event Q, he might see a figure near 35 I think since the light reaching him now came from when the clock said that. That's the only figure with complicated math, and that one is unimportant.
If Oscar sees a figure of 35, then it confirms that it is Edgar who is moving.
Noax wrote:In Edgar's frame:
After 388 minutes, Edgar has gone nowhere...
Only from his point of view.
Noax wrote:...but his clock reads 388...
How did it jump from 97 to 388?
Noax wrote:...and event Q happens 336 light-minutes to the right, which is Oscar and Irving meeting. Oscar's clock is running at half-speed, so it reads only 194.
Now it's Oscar moving. The speed of 0.866c is relative to Edgar; they can't both be going that fast.
Noax wrote:In Irving's frame:
Irving is moving at .866c to the left in Edgar's frame, so Edgar is moving .866c to the right in Irving's frame. Irving's clock reads 194 because he is just now at event Q syncing his clock to Oscar's. At event Q, Edgar's clock reads 679 minutes.
Note that simultaneous with the same event Q, Edgar's clock reads 97 in Oscar's frame...

That's in Edgar's frame, if indeed he is the one moving. In Oscar's frame, Edgar's clock reads 35 according to you.
Noax wrote:Still in Irving's frame, between events Q and R:
After 194 minutes, Irving has gone nowhere, but his clock reads 388, and event R happens, which is when Irving and Edgar meet.

In order that Irving and Edgar meet, they will have to be travelling at different speeds, relative to Oscar.
I dunno; this is doing my head in. Get back to me if I misunderstand and we'll take it from there, but I think this illustrates the problem of mistaking what you see for what there is.
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Noax
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Re: How does time work? Pt II Special Relativity.

Post by Noax »

uwot wrote:
Noax wrote:In Oscar's frame:
After 194 minutes, Oscar has gone nowhere, but his clock reads 194, and event Q happens, which is when Oscar and Irving meet. Irving at that time sets his clock to 194. Meanwhile, Edgar is 168 light minutes to the left of event Q, and his clock reads 97 at the same time as event Q since at the speed he's moving, his clock runs at half normal pace.
Well, if his clock reads 97, then it is Edgar that is moving.
Quite right. The paragraph is preceded by "In Oscar's frame". In anybody's frame, the others are moving. Those headers above each paragraph identifying the frame of the paragraph is very important. Nobody is objectively stationary, a concept with no meaning in SR.
Noax wrote:If Oscar tries to read Edgar's clock from event Q, he might see a figure near 35 I think since the light reaching him now came from when the clock said that. That's the only figure with complicated math, and that one is unimportant.
If Oscar sees a figure of 35, then it confirms that it is Edgar who is moving.
No, it is the fact that the paragraph was described in Oscar's frame that confirms it is Edgar who is moving (relative to that frame). In relativity, you can't say somebody is moving. It is always "moving relative to frame X". There is no objective moving (motion not relative to anything).
Noax wrote:In Edgar's frame:
After 388 minutes, Edgar has gone nowhere...
Only from his point of view.
By definition. Edgar's frame is, by definition, the frame in which Edgar is stationary. Same for the others.
Noax wrote:...but his clock reads 388...
How did it jump from 97 to 388?
In Edgar's frame, event Q (Edgar is not present there, it is some distance away) is simultaneous with the event of Edgar's clock reading 388. Simultanaity is completely frame dependent, and the figure of 97 was worked out in Oscar's frame, not Edgars. So in Oscar's frame, it only takes 194 minutes for Q to happen, and since Edgar's clock is the one moving, it ticks off only half that, so 97. In Edgar's frame, 388 go by, and Oscar's clock is moving at half speed, so it reads 194 at event Q. Notice that in the frame of either, the clock of the other runs half as fast. I chose the speed to get that factor of 2, to help keep the math simple.
Noax wrote:...and event Q happens 336 light-minutes to the right, which is Oscar and Irving meeting. Oscar's clock is running at half-speed, so it reads only 194.
Now it's Oscar moving. The speed of 0.866c is relative to Edgar; they can't both be going that fast.
It said "In Edgar's frame" above this part. Edgar is stationary here.
Noax wrote:In Irving's frame:
Irving is moving at .866c to the left in Edgar's frame, so Edgar is moving .866c to the right in Irving's frame. Irving's clock reads 194 because he is just now at event Q syncing his clock to Oscar's. At event Q, Edgar's clock reads 679 minutes.
Note that simultaneous with the same event Q, Edgar's clock reads 97 in Oscar's frame...

That's in Edgar's frame, if indeed he is the one moving. In Oscar's frame, Edgar's clock reads 35 according to you.
Nobody is "indeed the one moving". This is relativity, which has no such concept. In Oscar's frame at event Q, Edgar's clock reads 97. I said that at the top in the part labeled "Oscar's frame". If Oscar looks at Edgar's clock from that distance, he would not see 97 because Edgar is 168 light-minutes away, so the ~35 value is just what he sees, not what it is now. I told you the 35 figure is unimportant, and also not accurate, but it is somewhere around there.

Noax wrote:Still in Irving's frame, between events Q and R:
After 194 minutes, Irving has gone nowhere, but his clock reads 388, and event R happens, which is when Irving and Edgar meet.
In order that Irving and Edgar meet, they will have to be travelling at different speeds, relative to Oscar.
Yes, that is described at the top. From Edgar's frame, Oscar is moving to the right, and Irving to the left, both .866c. That means in Irving's frame or Oscar's, the other is moving more like .989c with a dilation factor of 7, but those two don't care about each other's clocks, so I didn't ever describe things between those two.
I dunno; this is doing my head in. Get back to me if I misunderstand and we'll take it from there, but I think this illustrates the problem of mistaking what you see for what there is.
Forget what anybody sees, since they see only the past if they're looking at something not in their own presence. Clocks are synchronized/compared only when they're in each other's presence, such as each of the 3 events. If something is in your presence, that is what is. If something is distant, then what you see is the past, not what is. The whole description I gave (except for the 35 thing) is about what is, not what is seen. Drop the preconception that there is "indeed the one moving or stationary" and it is not too hard to understand.
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Re: How does time work? Pt II Special Relativity.

Post by uwot »

Noax wrote:Nobody is "indeed the one moving".
This is the bit I don't get. If no one is moving, how do you explain the relative motion?
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Re: How does time work? Pt II Special Relativity.

Post by Noax »

uwot wrote:
Noax wrote:Nobody is "indeed the one moving".
This is the bit I don't get. If no one is moving, how do you explain the relative motion?
Didn't say nobody was moving. I meant there is no objective fact to it. The word 'indeed' implies that, like there is some fact about it somewhere and one of them is actually stationary and the other ones are wrong. Everything is stationary relative to itself.
In your blog post, there is an implication that Einstein is the one moving, and stickwoman is in fact stationary, but from Einstein's frame, stickwoman is the one moving, the one whose time is stretched out. Neither frame is in fact more correct. There is no fact of the matter. There is no preferred frame. Velocity is not a property of anything. It is a relation between and a thing and a frame designated as a reference.

So my car measures speed relative to the road under it. Without the road/planet under it, the speed of the car is meaningless.
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Re: How does time work? Pt II Special Relativity.

Post by uwot »

Noax wrote:Didn't say nobody was moving. I meant there is no objective fact to it.
I don't want to get into objective facts, but I think it is fair to say that at least one frame has to be moving for there to be relative motion. I understand that P, Q and R can be treated as discrete events for mathematical purposes; what I can't see is that all three can occur in a sequence that does not include acceleration.
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Re: How does time work? Pt II Special Relativity.

Post by Noax »

uwot wrote:
Noax wrote:Didn't say nobody was moving. I meant there is no objective fact to it.
I don't want to get into objective facts, but I think it is fair to say that at least one frame has to be moving for there to be relative motion.
A frame is moving relative to a different one, and the other one would then be moving relative to the first one.

You say a frame is moving, without referencing to what its motion is relative. That can't be. Without some reference designated as stationary, there is no defined velocity.

Look at it another way: Let than 1% of the matter in the universe has a speed less than .2c relative to our solar system. Are we really so privileged to be the only place in all existence that is <barely> moving? No, there is no such place, and no such frame as the stationary one, and no local experiment that can be performed to determine if you've stopped.
I understand that P, Q and R can be treated as discrete events for mathematical purposes; what I can't see is that all three can occur in a sequence that does not include acceleration.
They're points in 4D spacetime (in physics, points in spacetime are called events), and in any frame (not just the three frames mentioned in the story), they're temporally ordered P, Q, then R. For two events to be ambiguously ordered, they would need to be out of each other's light cone precluding anything from being present at both events. Nobody accelerated in my story at any point. It was the whole point of wording it that way, to avoid the complications of acceleration. But if Oscar had waited for event Q and then let himself get seriously smacked by a celestial cricket bat altering his trajectory to the one of Irving, then it would have been a story with acceleration but still all the same numbers as before, and I would have had to specify Oscar's frame before or after the cricket-bat smack since his frame would change at that point.
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Re: How does time work? Pt II Special Relativity.

Post by uwot »

Noax wrote:
uwot wrote:I understand that P, Q and R can be treated as discrete events for mathematical purposes; what I can't see is that all three can occur in a sequence that does not include acceleration.
They're points in 4D spacetime (in physics, points in spacetime are called events)...
Well, in your story, there is only x and t. I understand about relative motion and that P, Q and R are events. It's frustrating that you think I need tutoring. What I clearly am not getting across is that the relative motions in those three events are incompatible. It only works if at any of those three events you ignore the relative motion specified in the other two.
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Re: How does time work? Pt II Special Relativity.

Post by Noax »

uwot wrote:Well, in your story, there is only x and t.
There is a y and z dimension as well, but none of the character deviates from the others in either of those two dimensions, so they are not part of the math. It is an out and back situation, as simple as I could make it.
I understand about relative motion and that P, Q and R are events. It's frustrating that you think I need tutoring.
I'd not care so much if you were not blogging a tutorial of sorts. What you had was pretty correct but incomplete. Stickwoman also needs one of those little mirror thingys that Einstein has so it can be shown that hers runs slower than Einstein's because her light takes the longer zigzag path in the train's IRF. You seem to be resistant to that given your replies to my comments.
What I clearly am not getting across is that the relative motions in those three events are incompatible. It only works if at any of those three events you ignore the relative motion specified in the other two.
"Relative motion in those three events"? Not sure how to parse that. Events have neither motion, velocity, nor any frame. You didn't say "motion of these events", so perhaps that's not what you're asking. So no, I don't know what you're trying to get across.
There are three frames, and the story can be described from any of those frames, and I've tried to tell the same story from the point of view of multiple reference frames. Each paragraph is carefully preceded by identification of the frame defining who is stationary for that paragraph. In every case, the clock of the moving person runs half the speed of the stationary one (not Oscar vs Irving, whom I never compare. Their dilation factor happens to be very close to 7x, not 2x). The moving person always goes 84 light-minutes each 97 minutes, which is really close to .866c that gets you the 2x time dilation. Show me any paragraph that is not consistent with what I just stated here. I took a couple days to proofread and get it right, but maybe I messed up somewhere. The names and numbers are my own. I did not copy this story from anywhere.
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Re: How does time work? Pt II Special Relativity.

Post by uwot »

Noax wrote:I'd not care so much if you were not blogging a tutorial of sorts.

I don't think the blog will make it onto the reading list of any physics curriculum.
Noax wrote:What you had was pretty correct but incomplete. Stickwoman also needs one of those little mirror thingys that Einstein has so it can be shown that hers runs slower than Einstein's because her light takes the longer zigzag path in the train's IRF. You seem to be resistant to that given your replies to my comments.
Yes, because the blog is about what actually happens. I agreed with you that subtitling that page 'special relativity' was misleading and have removed that. Kinematic time dilation is a consequence predicted in SR, but real world kinematic time dilation is not a result of the idealised situations described in SR. Clocks really do show that they have run slower or faster, when compared to clocks they have been moving relative to.
Noax wrote:I took a couple days to proofread and get it right, but maybe I messed up somewhere. The names and numbers are my own. I did not copy this story from anywhere.
I will look at it again to do it justice and make sure I haven't messed up, but it is nothing to do with my blog.
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