Relativity of Simultaneity | Special Relativity Ch. 4

The previous videos in this series:

This video is chapter 4 in my series on special relativity, and it covers how things that appear simultaneous from one perspective in our universe aren't simultaneous from other moving perspectives - that is, from inertial reference frames moving at different speeds. This is explained via the Lorentz transformation of coordinates of the events in question, enacted with a mechanical minkowski diagram, aka mechanical Lorentz transformation, aka spacetime globe.

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Created by Henry Reich

[acapellascience]

This series has already given me more intuition for relativity (especially simultaneity problems) than I got from two physics degrees.

[MisterAppleEsq]

“Simultaneously spontaneously combust” is fun to say.

[thomas.]

Why do people simultaneously claim to be first? Maybe because in their worldlines they are first while they are in fact simultaneous to some other observer? Who knows....

[livewireOrourke]

"The takeaway here is that our universe has neither an absolute notion of time..."


I tried explaining that to my boss last time I was "late" for work.

Needless to say, it fell on deaf ears.

[abhishuoza]

Take that, people who comment 'first' !

[itsrudetostare]

*Pretends to understand whats going on*

[vtron]

Space Time Grids should one day be as common as globes

[justinz.]

If I play this video at half speed do I understand twice as much or cut my learning over time in half?

[rakshitharsh]

Einstein was great
But your videos are awesome

[JugheadJones]

Seeing stuff like this always makes me feel we are just living in an amazingly advanced graphic engine! : )

[phil]

I love this relativity series. It’s awesome that you’re making relativity accessible to people who would otherwise know nothing about it

[WilliamDye-willdye]

For me, the "oh, I get it now" moment was at 2:18, when he connected relative event-time to relative position. Well done.

[TaliesinMyrddin]

I like how the square thing moves stuff

[PKMKB]

I understood everything but from 0:00 I LOST IT

[HXO]

Do the boxes not burn at the same time but it just takes light longer to reach the other person to 'notify' him of this since the boxes are not the same distance away from him?

[saultcrystals]

How out of sync will events be when observed from 10 billion light-years away or on opposite sides of the observable universe? Since objects at this distance have incredibly high redshifts (i.e., they're moving away from us incredibly fast), how does this affect the apparent distortion? How successfully have astronomers and astrophysicists incorporated these effects into their observations, calculations, theories, etc.?

[feynstein]

Lovely video, Henry. But I CAN'T believe you didn't give us the full story. Relativity of simultaneity only works for causally unconnected events. If event A causes event B, then all frames of reference will agree that event A happened before event B. In terms of spacetime diagrams, relativity of simultaneity applies only to those events that lie outside an observer's lightcone. This basically means that these are (causally) irrelevant events and it doesn't matter (to you) which event happened before which, because neither event can affect you.

[ewutermohlen]

"Moving perspective" is a thing that changes location relative to another thing. I understand why some people don't get it, because they didn't watch and understand the previous video's.
Great video on this topic, easy to follow and visually apealing.

[jedijeremy]

Nice work as usual! But... I suspect a lot of people are going to misunderstand an important part of what's going on here, and conflate the concept of light propagation delays for what the Lorentz transform really means. It's very easy to write it off as "what appears simultaneous for me appears not for you because you're at a different _distance_ ". If two supernova go boom, and I'm in the middle, it _seems_ simultaneous for me, but obviously if you're closer to one of the big badda-booms, that one _seems_ to come first. I think you need to make it a little more clear that spatial distance is irrelevant... if the 2nd observer is whooshing past you at significant speed and barely grazes your elbow (so you're both basically at the same position, but with a different velocity) they will STILL see the ka-booms happen at different times. Isn't that the key point that causes sane people to question their entire concept of reality, and you hear the delicious sound of brains breaking? Not "I was over here and I saw something different" but "How can we be disagreeing when I WAS THERE TOO?" ...did I get that right?

[agiar]

So, if from perspective α, two events can be simultaneous and yet not simultaneous from perspective β, then it also follows that a scenario can be arranged whereby, from perspective α, event A occurs first followed by event B, whereas from perspective β, event B occurs first, followed by event A.

Does this introduce problems with causality? Could the scenario be such that someone with perspective α reasonably conclude that events A and B are related, and that, since they are related and since A occurred first, then A _caused_ event B? If so, then such a claim would be nonsense to perspective β, since it is a premise of basic causality that effects cannot precede their causes.

This seems vaguely reminiscent of the sorts of paradoxes that arise when one hypothesizes reverse time-travel, wherein one could take an action to cause or prevent something that had already happened.