100 years since first proof of Einstein's General Relativity

ack

VIP/Donor & WBF Founding Member
May 6, 2010
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Boston, MA
#1
A great read of how one solar eclipse on May 29 1919 first proved General Relativity by confirming gravitational lensing, at https://www.forbes.com/sites/starts...einstein-right-and-newton-wrong/#22eaa67d1610 similar to NorthStar's recent article by The Guardian

In Newton's gravity, anything with mass attracts anything else with mass. Even though light is massless, it has an energy, and therefore you can assign an effective mass to it through Einstein's E = mc2. (You find that m = E/c2.) If you allow a photon to pass near a large mass, you can use this effective mass to predict how much the starlight should bend by, and you get a specific value. Near the limb of the Sun, it's just under 1" (arc-second), or 1/3600th of 1°.


But in Einstein's General Relativity, both space and time are distorted by the presence of mass, whereas in Newton's gravity, only an object's motion through space is affected by the gravitational force. This means that Einstein's theory predicts an extra factor of 2 (actually slightly more, especially as you get closer to the mass in question) over Newton's, or a deflection near the Sun of closer to 2".

An illustration of gravitational lensing showcases how background galaxies — or any light path — is distorted by the presence of an intervening mass, but it also shows how space itself is bent and distorted by the presence of the foreground mass itself. Before Einstein put forth his theory of General Relativity, he understood that this bending must occur, even though many remained skeptical until (and even after) the solar eclipse of 1919 confirmed his predictions. There is a significant difference between Einstein's and Newton's predictions for the amount of bending that should occur, due to the fact that space and time are both affected by mass in General Relativity.

According to Newton's theory, [Mercury's] orbit should have precessed by 5,557"-per-century, due to the precession of Earth's equinoxes and the gravitational effects of all the planets on Mercury's orbit. But observationally, we observed 5,600"-per-century instead. That difference, of 43"-per-century (or just 0.00012°-per-year), had no explanation in Newton's framework. Either there was an extra planet interior to Mercury (which observations ruled out), or something was wrong with our old theory of gravity.

But Einstein's new theory could explain the mismatch. He spent years developing the framework for General Relativity, where gravitation wasn't caused by masses attracting other masses, but rather by matter and energy curving the very fabric of space, which all objects then move through. When gravitational fields are weak, Newton's law is a very good approximation to what Einstein's theory laid down.
 

Tim Link

New Member
Feb 12, 2019
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#3
Right on Ack, one of my main reading interests in life...the universe and everything inside of it.
Me too! I wonder though, does the universe contain itself? I think of the universe as including anything and everything that exists in any way at all, which would include the universe.
 
Likes: NorthStar
Feb 8, 2011
21,411
487
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Vancouver Island, B.C. Canada
#4
Some say the universe is a gigantic black hole, others talk about multiverse.
I have no clue, I'm just fascinated by it all. :)

And I find our planet Earth a beautiful blue planet to live on, with rich tropical forests, flowers, animal kingdom, with the human species always pushing the envelope into space exploration, and music listening.
 
Likes: Tim Link

ack

VIP/Donor & WBF Founding Member
May 6, 2010
5,545
195
63
Boston, MA
#5
Sometimes, I find myself attempting to understand the enormity of the universe and accepting that it may be part of a giant black hole, which keeps feeding itself, potentially explaining the ever-growing rate of expansion. But at the same time, I tend to think that it cannot be so simple, and the real truth is probably more enormous than our brains can comprehend, much like trying to comprehend that possibly, it all sprung up from absolutely nothing.
 
Likes: Tim Link
Feb 8, 2011
21,411
487
83
Vancouver Island, B.C. Canada
#6
Some race cars, others climb the highest peaks, and the rest build giant telescopes and spaceships. There is so much space around us that we can't see the edges.

I like laying in the grass or in an opening of a mountain forest in the summertime to observe the night sky, the multitude of white stars, the flying ones included, and have my head and eyes facing the North winds. ...The Northern lights.

There is a meaning to our existence ... the search for the immensity.
 

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