# Interesting science

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• #1614170
Doing my best
Participant

I saw that according to Einstein, if you traveled at a significant percentage of the speed of light, time for you would slow down but not for those who are moving much slower pace. Therefore when you stopped and came back to earth you will be traveling into the future and skipping some years because for those who were stationary time moved faster.
Anyone know more about this? or how this would work?

Also, anyone know how a wormhole would work?

#1614309
Joseph
Participant

First explain the difference between special relativity versus general relativity, and then you’ll understand the answer to your question.

#1614351
Meno
Participant

There is a similar concept which is actually observable.

Gravity affects the passing of time just like speed does. If an astronaut goes to outer space with a very accurate clock, while leaving an identical clock on Earth, when he returns there will be a small discrepancy between the two.

#1614365
DovidBT
Participant

The Wikipedia article on “time dilation” has a detailed explanation of this effect.

#1614460
Avram in MD
Participant

Doing my best,

“Anyone know more about this? or how this would work?”

Einstein used a thought experiment involving a speeding train to demonstrate that time is relative to the inertial frame of the observer.

Suppose there is a speeding train, and there is a man in the middle of this train. Another man is sitting at a platform outside of the train as it speeds past. Right as the middle of the train is passing the platform, the man on the platform sees lightning strike both ends of the train simultaneously. What does the man inside the train observe? As light from the lightning heads towards his eyes, the train is moving in the direction of one of the bolts, and away from the other. Thus, the light from the lightning strike at the front of the train has a shorter distance to travel to the eyes of the man in the train than the light from the strike in the back. So he’d say the strikes were not simultaneous.

#1614812
Doing my best
Participant

Thanks Meno, dovid, and avram.
Joseph,
i have no idea what you’re talking about.

#1614867
Joseph
Participant

DMB: Once you’ve earned your Ph.D in physics, you’ll understand

#1615062
Yserbius123
Participant

Yes, it’s called the Theory of Special Relativity. The formula for figuring out how time passes is called the Lorentz Equation. It’s hard to wrap your brain around it, but bekitzur it’s like this.

Einstein proved that speed is always relative except light. Vos zugst du? Lemme explain. If I’m standing still, and my father drives passed me, I see a car driving at 87 mph. But if I’m riding a bike at 17 mph and he passes me, I only see him driving 70 mph. Because motion is relative to the motion of whatever is measuring it. Except for the speed of light. When I turn on a flashlight, imagine it to be a gun shooting out tiny little balls called “photons”. Photons travel at 186,000 miles per second. Scientists call that number “c”. So if I’m shining a flashlight and the beam passes my Tatti, he sees photons fly past him at 186 thousand miles per second. But let’s say he’s flying in a super rocket that’s traveling at 100,000 mps. He does not see the photos from my flashlight travel at 86,000 mps, he sees them traveling at the same speed I see them. Because when he’s going faster, time is going slower. So he sees me and everything around me moving faster, (and if he keeps up the pace soon I will be older than him) including the light beam.

Hope that helps.

#1615063
Yserbius123
Participant

I’ve always found Brian Greene to have the best explanations on physics. Gerald Schroeder gives a good one too, if you want something from a frum perspective.

#1615522
Doing my best
Participant

Avram,
I was thinking more about the train mashal and i don’t get it. Suppose the man on the platform was not at the middle of the train, but closer to the front. He would also see the strikes not as simultaneous, but rather he would see the front one first because it’s a shorter distance. this should prove that the train example has nothing to do with the train moving.

Yserbius,
Why is time for him moving faster?

Joseph,
I’m not running to college just because you want to sound sophisticated, please explain or don’t make things sound even more complicated.

Anyone know how to explain this stuff simply?
And anyone know what a wormhole would do and how you can make one?

#1615531
Participant

Because when he’s going faster, time is going slower.

?

So if a person goes on an airplane and it accelerates to whatever it’s supposed to accelerate to, time is going slower then?

#1615629
ubiquitin
Participant

“So if a person goes on an airplane and it accelerates to whatever it’s supposed to accelerate to, time is going slower then?”

Yes!
Though note even a jumbo jet while traveling fast at say 550 mph (~ 0.15 miles per second) is nothing compared to the 186,000 m/sec that light travels. so it is not noticeable but it is real and even measurable! w/ atomic clocks.
look up “time dilation at low speeds” for a nice explanation with concrete numbers

#1615721
Meno
Participant

I was thinking more about the train mashal and i don’t get it. Suppose the man on the platform was not at the middle of the train, but closer to the front. He would also see the strikes not as simultaneous, but rather he would see the front one first because it’s a shorter distance. this should prove that the train example has nothing to do with the train moving.

In your case the two men would still observe the events differently (i.e. different intervals of time between the two lightning strikes) due to the fact that the train is moving.

anyone know what a wormhole would do and how you can make one?

PM me

#1616091
DovidBT
Participant

And anyone know what a wormhole would do and how you can make one?

I make wormholes as a hobby. I usually sell them on Ebay or Craigslist. I’d be happy to give one to a fellow Coffee Roomer, but, unfortunately, we can’t post links here.

#1616154
Doing my best
Participant

In regard to atomic clocks, would all clocks be a little off since you carried it home from the store?

“In your case the two men would still observe the events differently (i.e. different intervals of time between the two lightning strikes) due to the fact that the train is moving.”
Yes, but the man on the platform will not see the strikes at the same time. This should prove that it is not only movement which can change your perception.
Also, if the man on the train had super long hands and one was in front of the train and and the other in back, he would feel both strikes at the same time. this should show that time has not slowed. And even though he sees them at different times, that’s because of the fact that the back light hasn’t hit him, but it’s still there.

#1616198
000646
Participant

Doing my best,

The concept is actually not that complicated once you understand it although the mathematics involved can be quite complicated.

What Einstein discovered was that what we call “time” is actually another dimension in the universe in the same way the 3 spatial dimensions are dimensions. This 4 dimensional fabric is called “spacetime”. Everything “moves” through this fabric at a constant speed of 186,000 miles per second. This speed is a constant.

When you aren’t moving in any of the spatial dimensions all of your speed is through the time dimension. If you move through the space dimension you lose some of your speed through the time dimension. Practically this means that time passes slower for you. This is similar to the way that a car going northeast goes slower in the northern direction then a car going straight north. Since the speed of light is so fast when we move through the spatial dimensions the affects are not noticible. If however you managed to move through space at close to the speed of light the fact that you are passing time much slower then someone standing still who is just speeding through time will become very apparent.

#1616248
Meno
Participant

“Yes, but the man on the platform will not see the strikes at the same time. This should prove that it is not only movement which can change your perception.”
.
Well of course his position in space also affects his perception. If you and I are both standing still at different spatial distances from an event, we will observe that event at different times. Einstein’s chiddush is that speed also affects perception.

“Also, if the man on the train had super long hands and one was in front of the train and and the other in back, he would feel both strikes at the same time.”

מהיכא תיתי?

#1616807
Doing my best
Participant

I GET IT!
thanks 646.

#1617846
Doing my best
Participant

I was thinking some more, and i was trying to understand the following. If time is everything moving through something, how do we know the train isn’t going backwards on this thing?

#1617878
StuartW
Participant

This conversation has focused only on special relativity.
General relativity factors in gravity as well.

Both these relativitiess cause gps satellites’ clocks to differ from clocks on earth.

The best way to learn this stuff is by google searches.

#1617909
000646
Participant

Doing my best,

I’m not sure I understand your question.

#1618006
000646
Participant

The train Moshol just demonstrates one of the weirder consequences of the theory of relativity known as the “relativity of simultaneity.” Practically this means is that events that are simultaneous to one person are not necessarily simultaneous to anyone else.

In the train Moshol to the guy on the platform both strikes ACTUALLY happened at the same time. He knows this because if he measured the distance traveled by the light from each strike and the speed of that light he’d see that they both traveled the same distance at the same speed and hit his eyes at exactly the same time.

For the guy on the train the strike happening on the end of the train in the direction of the trains movement relative to the platform ACTUALLY happened first and the strike that happened at the opposite end of the train ACTUALLY happened after. He knows this because if he was to measure the distance and the speed traveled by the light from the strike in the direction the train is going he would see that it covered the same amount of distance as the strike at the back of the train at the same speed as the strike that hit the back of the train (the speed of light is a constant) and the light from it still hit his eyes first.

Neither the observer on the platform or the observer on the train are wrong. On the train the strikes were not simultaneous and on the platform they were.

It’s amazingly weird and the consequences get stranger and stranger the more you think about it.

#1618077

That is so fascinating. Thanks for the explanation

#1618879
Avram in MD
Participant

Doing my best,

“Yes, but the man on the platform will not see the strikes at the same time. This should prove that it is not only movement which can change your perception.”

True, he wouldn’t, but he’d know that the strikes occurred at different distances from him, and, doing the math, he’d still calculate that the strikes occurred simultaneously. Setting up the thought experiment with the two strikes being equidistant from both observers is done for simplicity, but it doesn’t change the fact that in one man’s inertial frame of reference the strikes were simultaneous, and in the other man’s frame of reference they were not.

Also, if the man on the train had super long hands and one was in front of the train and and the other in back, he would feel both strikes at the same time.

No he wouldn’t. Let’s say his nerve signals could go from his hands to his brain at the speed of light, i.e., the signals are moving towards his brain at the same speed as the light from the flashes (in reality they go more than a million times slower). As we saw above, the light/nerve signal from the front of the train arrives to his brain before the light/nerve signal from the back of the train. So he both sees and feels the strikes as non-simultaneous. The truth is, they were non-simultaneous to him. Just as much as they were simultaneous to the guy on the platform.

And even though he sees them at different times, that’s because of the fact that the back light hasn’t hit him, but it’s still there.”

That can only make sense if the speed of light from one flash was slower than the speed of light from the other flash, which is impossible.

#1619868
Doing my best
Participant

“That can only make sense if the speed of light from one flash was slower than the speed of light from the other flash, which is impossible.”
Why? The light in front of him moved closer to him when the train moved towards it. (the same way when two cars go towards each other they meet other faster then when only one moves.) however, he is sort of running away from the photons behind him, so it will take them longer to hit him, however they are still there.

646,
this is my question,
in this time dimension we’re all moving in certain direction, right?
So then when we move, we’re going a little faster than everyone else in this dimension, and therefore time passes faster, correct?
But according to that, wouldn’t it be that if i move in a different direction, I should be going backwards in this time dimension?
Why am i always heading forward when i move?

#1620136
000646
Participant

Doing My Best,

We are always moving in one direction through spacetime. The speed we move at is a constant 186,000 miles per second. It’s like your in a car that is stuck moving forward at a constant speed of 186,000 miles per second. This car has no break or reverse option, and the steering wheel won’t allow you to make a 360.

When due to inertia you are sitting still in the spatial dimensions all of your movement is through the time dimension. If you start moving in the spatial dimensions you pass through less time because some of your speed is diverted to the the spatial dimensions you are moving in (time passes slower for you). This is why light or any other massless thing must move through space at 186,000 miles per second. There’s nothing holding it still in any of the spatial dimensions.

When you move in one of the spatial dimensions It’s like you turned your car northeast as opposed to straight north. Your still moving forward but you will now cover less ground in the northern direction then a car going straight north. You can’t slow down or speed up this movement through spacetime. You also can’t change the direction of this movement. You can move through more of one of the dimensions or another, in the same way you can angle the car in my example a bit east but your direction in spacetime is always a straight line forward.

#1620188
Avram in MD
Participant

Doing my best,

Why? The light in front of him moved closer to him when the train moved towards it. (the same way when two cars go towards each other they meet other faster then when only one moves.) however, he is sort of running away from the photons behind him, so it will take them longer to hit him, however they are still there.”

Why are the photons playing “catch-up” with the man on the train, and not the man on the platform? What’s special about the platform man that you take his side? Let’s dispense with the train and the platform, and say our two men are in spaceships whizzing past each other out in open space. And let’s say each man believed his spaceship to be at rest (“Full stop, ensign!” “Yes, captain!”). One man therefore thinks that he is “stopped”, and the other ship is moving past him, and the other thinks that his ship is “stopped”, and the other ship is moving past him! And suddenly there are two flashes of light nearby both ships. Both men think that his own ship is stopped, and the light from both flashes is moving towards each of the men at the speed of light. For one, the flashes were simultaneous, and for the other, they were not. Which is right? Both, relative to their own inertial frame of reference!

#1620279
Meno
Participant

I’ve been thinking about it more, and I’m having trouble with the train example.

First let’s take a simple case: Light travels 186,282 miles per second. Let’s say I’m running in a straight line at 1000 miles per second, and lightning strikes exactly 186,282 miles ahead of me. How much time passes (on my watch) before I see the lightning? The answer, I believe, is exactly 1 second, because light travels the same speed in every reference frame – that’s Einstein’s chiddush.

So now the train example. To make it simpler, lets say the train is 372,564 miles long (2 x 186,282 miles). The guy on the platform sees both lightning strikes simultaneously after 1 second – simple. But why doesn’t the guy on the train also see them simultaneously? Why is it different from my case? Is my conclusion in my case incorrect?

#1620332
Avram in MD
Participant

Meno,

“First let’s take a simple case: Light travels 186,282 miles per second. Let’s say I’m running in a straight line at 1000 miles per second, and lightning strikes exactly 186,282 miles ahead of me. How much time passes (on my watch) before I see the lightning? The answer, I believe, is exactly 1 second, because light travels the same speed in every reference frame – that’s Einstein’s chiddush.”

Correct.

“So now the train example. To make it simpler, lets say the train is 372,564 miles long (2 x 186,282 miles). The guy on the platform sees both lightning strikes simultaneously after 1 second – simple. But why doesn’t the guy on the train also see them simultaneously? Why is it different from my case? Is my conclusion in my case incorrect?”

The flashes were 186,282 miles from each observer, so they both figure that the light from each flash took 1 second to reach them. But the observer on the platform saw the flashes as happening at the same time, and the one on the train saw the flash at the head of the train happen first. In the inertial frame of the platform observer, the man on the train was moving away from the light coming from the back flash and towards the light of the front flash, so the light from the front flash traveled less than 186,282 miles before reaching him, and the light from the back flash traveled further than 186,282. But to the man on the train, the light from each flash traveled exactly 186,282 miles before reaching him.

#1620312
000646
Participant

Meno & Doing My Best,

From the reference point of the man standing in the middle of the train, he is standing still. Yet the strike that hit the front of the train still reaches his eyes first, even though it traveled the same distance at the same speed at the strike that hit the back. The only explanation for this is that the strike that hit the front of the train happened first. In the reference frame of train man the strikes were not simultaneous.

From the perspective of the guy on the platform HE (platform man) is standing still, therefore if he measures the strikes he will see that the light from the strikes both traveled the same distance at the same speed and hit his eyes at the same time. The only explanation for this would be that the strikes were simultaneous.

Both Platform Man and Train Man will agree that the light from the bolt that hit the front of the train hit Train man’s eyes first, they will just disagree on the reason: Train man will say it is because the bolt in the front of the train happened first and Platform man will say it’s because train man was moving forward.

#1620640
Meno
Participant

From the reference point of the man standing in the middle of the train, he is standing still. Yet the strike that hit the front of the train still reaches his eyes first

In less than one second? That would mean light is travelling faster than the speed of light in train man’s reference frame. That’s impossible.

I think this is what Avram is saying, and I think it works out:

The discrepancy is not in when the light hits each observer’s eyes. Train man will see two lightning strikes simultaneously and platform man will see two lightning strikes simultaneously.

The discrepancy is in when each observer sees the light hitting train man’s eyes. From train man’s reference point, the light beams from both strikes hit his eyes simultaneously (that’s why he observes the strikes as occurring simultaneously). From platform man’s reference point, the light beams from both strikes do not hit train man’s eyes simultaneously. In other words, platform man sees the strikes occur simultaneously, but he does not see them reaching train man’s eyes simultaneously.

#1620647
000646
Participant

Meno,

It would not mean that light from the strike in front is traveling faster then the speed of light from Train mans perspective it traveled the same distance and the same speed as the strike that hit the back. It just happened first.

#1620651
000646
Participant

For Train man the strike happening in the front of the train happening first. For Platform both strikes happen simultaneously.

Train Man knows that the strike in front of the train happened first because from his perspective he is standing still and the light from both strikes traveled the same distance at the same speed and the light from the strike in front of the train hit his eyes first.

Platform man knows that they happened simultaneously. He knows this because in his frame he is standing still and the light from both strikes traveled the same distance at the same speed and hit his eyes at exactly the same moment

#1620653
Avram in MD
Participant

Meno,

“In less than one second? That would mean light is travelling faster than the speed of light in train man’s reference frame. That’s impossible.”

No, on his watch it’ll be a second. On the platform man’s watch, it’ll be less than a second.

“The discrepancy is not in when the light hits each observer’s eyes. Train man will see two lightning strikes simultaneously and platform man will see two lightning strikes simultaneously.

The discrepancy is in when each observer sees the light hitting train man’s eyes. From train man’s reference point, the light beams from both strikes hit his eyes simultaneously (that’s why he observes the strikes as occurring simultaneously). From platform man’s reference point, the light beams from both strikes do not hit train man’s eyes simultaneously. In other words, platform man sees the strikes occur simultaneously, but he does not see them reaching train man’s eyes simultaneously.”

The platform man observes the following: Two flashes that happened simultaneously at the moment the middle of the train (and the train man) passed him, by calculating that the light from each flash reached him exactly 1 second after the actual strike.

The train man observes the following: Two flashes, with the flash at the front of the train happening just before he passed the platform man, and the flash at the back of the train happening just after he passed the platform man, by calculating that the light from each flash reached him exactly 1 second after the actual strike.

The platform man observes the following about the train man: he was speeding towards one of the flashes at the same time the light from it was heading towards him, so the light reached him in under a second. He was moving away from the back flash, so that light reached him after slightly longer than a second.

The train man observes the following about the platform man: he was speeding towards the back flash, which happened later than the front flash, so the light from the later back flash reached him at the same time as the light from the earlier front flash, which he was moving away from.

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