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Physics, Astronomy & Cosmology / How do we know that particles are entangled?

« on: 25/06/2023 18:50:54 »

How do we know that two electrons, for example, are entangled?  When we observe one electron, how do we know that the other has taken on the opposite spin at that moment?

I hope this isn't the most obvious question ever asked here, but I don't think I have ever understood the answer.

I think I have a pretty decent understanding of QM and physics in general, but if someone can explain it simply that would be very much appreciated.

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Physics, Astronomy & Cosmology / Why does this twin paradox thought experiment fail for me?

« on: 19/01/2023 03:53:23 »

I can't seem to wrap my head around why this twin paradox thought experiment fails. 

In the image below from the website http://www.mysearch.org.uk/website1/html/250.Twins.html , they try to explain why the two situations are not symmetric, but I don't understand their approach.  Even if the website is not giving a sufficient explanation, I would still like to know why the two diagrams are not symmetric.

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Physics, Astronomy & Cosmology / What is the exact cause of the time dilation of the twin?

« on: 11/01/2023 18:46:12 »

Please read before commenting because I found some contradictory claims from two credible sources.

Here is a link that Fermilab put out,

.  At 12:00, it explains that the reason for the time dilation of the twin is because of the change in direction and not acceleration (although he does say that acceleration plays a small part).

The other claim is made by Sabine Hossenfelder.  She says in this video,

, at 11:00, that it is the acceleration that causes the dilation.

There must be a simple formula to calculate the time dilation by the acceleration.  This seems to be a way to know who is correct.

Any thoughts about this?

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Physics, Astronomy & Cosmology / Does time have more than one direction?

« on: 09/12/2022 15:59:39 »

Note: Title changed from "Does light have more than one direction?".
Assuming light time has a direction, an object in reference to itself travels only through time in a certain direction. If an object travels away from the object at rest, then according to the object at rest, it will have a spatial component to its direction.

I can't figure out how these objects can both be travelling through time in only one direction.

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Physics, Astronomy & Cosmology / How does special relativity explain dimensional components ...

« on: 24/06/2022 23:28:58 »

of space and time of a moving observer and a observer at rest?  So if object A observes object B coming towards it very fast, A is at rest and should only have the time component and no spacelike component.  But B can say the same thing.  How does SR explain the componentry of this kind of scenario?

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Physics, Astronomy & Cosmology / Is this a paradox in general relativity?

« on: 14/05/2022 06:08:03 »

I hope I can get some help here.  I can't figure out how this simple thought experiment is incorrect.

According to a pretty good looking analysis of length contraction and time dilation, the author makes a diagram of a spaceship travelling very fast towards the right side of your screen.  At the higher of the 3 clocks/events is the nose of the ship according to an observer on the ground and so is the clock/event below it.  For the diagram, here is the link, and just watch from 6:30 to 7:00

.

Now my thought experiment is about what might happen if an object moves really fast in front of the nose of the ship where the lower clock/event is.  To make the object appear in front of the nose almost instantaneously, we will say that it came from another spatial dimension z going into your screen.  For simplicity sake, let's say this interaction happens at the lower clock/event (where the nose of the ship is).

If an interception between the contracted nose (the lower clock) and the object is possible in the scenario given, it would seem that there would be an interaction with the nose of the ship that will never happen with the nose of the ship in the future (the higher clock).

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Physics, Astronomy & Cosmology / Why are large astronomical and relatively dense objects

« on: 26/01/2022 18:06:52 »

usually spherical when in a rest frame?

Isn't this a coincidence since relativity says that structures like the moon also exist as disk-like shapes to sufficiently fast frames of reference?

In other words, why do large spherical objects seem to favor rest frames?

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Physics, Astronomy & Cosmology / Is this a correct spacetime diagram with world lines?

« on: 20/01/2022 20:03:45 »

The diagram has 3 objects in it with 3 world lines in yellow.  There is a rock traveling really fast through the origin in the primed frame.  There are 2 more rocks at rest in the unprimed frame.  I also put the rocks on the x' axis just to remind me what is happening in the frame of reference of the rock that is traveling.  Is all of this roughly correct?