Astronomy - General Relativity (12 of 17) Proof of Theory: Gravitational Lensing, Einstein's Cross

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We will learn the proof of the theory of Gravitational Lensing and Einstein's Cross and comparing it with a convex lens and an observed object.

Next video in this series can be seen at:

[aaaaa]

If you are looking this video expecting for an answer why it is a cross, you will be disapointed.

[nesmanour]

Thanks a bunch prof.. keep up the good work 💎💙

[michaelglynn]

If I'm a photon zipping along, and skirt a star or galaxy and then lensed around it, do I resume my original trajectory or am I deflected at the angle I leave the lense?

[bbartt]

Why is it a cross shaped? Shouldn't it be a ring? I would assume the space is curved in all directions around the galaxy that acts as lens.

[tahycoon.]

could you please make a playlist of physics that review all the topics in a nutshell
i will almost finish the whole physics and i really need a review 👏🙏🙏🙏🙏🙏

[nnenone]

S'/S = 0.05.... so how is this a magnified image?

[theultimatereductionist]

Last time I took physics was in college: just first semester. Part of chemical engineering program.
I excelled in physics in high school. But, there is something I do not get: Einstein's Correspondence Principle.
Take a single object - a sphere - sitting alone in the universe. So no other objects for reference.
Now spin it. How would the object know it is spinning?
In one coordinate system, (x, y, z), a point at (x, y, sqrt(x^2+y^2)) remains at (x, y, sqrt(x^2+y^2)) for all time t.
Relative to different coordinate system, (x2, y2, z2), we have (x2(t), y2(t), z2(t)) = (R*cos(b*t), R*sin(b*t), 0)
where (x2, y2, z2) is a rotating non-inertial frame relative to (x, y, z) and of course vice versa.
But how does the object know that? So, does somebody on this object feel a centrifugal force or not, pushing them away from the sphere?

[samikatto]

every observation related to general relativity can be explained with differind field density. it is also alot simpler explanation and does not have any time or space nonsense. most laws in physics are not about universe but about our ability to comprehend and make sense of things. univerese does not care if things make sense for us. concepts we have like time, space, causality etc. are not facts about universe but about our need to categorize to make sense of things. universe might literally be unpredictable and we giving it qualities may be just warping it to our needs and desires. speed of light is just how fields change and for there to be observable change, there needs to be slowness somewhere.

[rhoddryice]

I watched a video the other week about a mission concept using the sun as a gravitational lens for imaging exoplanets at incredible resolution. But the swarm of telescopes would need to reach 550 AU to get the focal point right.


And I think that David Kipping at Columbia University approached the Juno team with a suggestion to use Juno with Jupiter as a gravitational lens. I think they were sceptic at first but are considering to try at the end of the mission.

[quantumofspace]

Can you take a fresh look at the universe? PATENT KZ-33869 An easy-to-understand experiment is proposed to create and study super-powerful, stable gravitational waves, the signal of gravitational waves exceeds the noise, or the speed of light in a vacuum is not constant. The choice is yours.

[pcpc]

this is super siper foolish analysis of phenommena in heavens/galaxies