Einstein’s biggest blunder

Hello everyone, today we’re going to talk about Einstein’s biggest blunder was actually not a blunder. This is very interesting, let’s get started. So this is Einstein’s field equation, Einstein came up with this equation from his general relativity, don’t worry about these details, this equation, the concept is very simple. This is telling, the right side is matter, and the left side is space, curvature of the space, and this equation is telling us that if this is, there’s a matter, matter has a gravity, and then with this gravity matter is gonna curve the space time. Okay, matter tells space how to curve.

And then, if the space is curved, space tells matter how to move, so if the space is curved, matter or light moves along this curved space down. That is, Einstein’s equation is telling us. And when Einstein came up with this equation, Einstein noticed that this right side is a matter, and a matter has gravity, and gravity is a pulling force, so, if there’s so much matter in the universe and it’s all affecting a pulling force, universe itself is going to shrink, because it’s a brain (not sure) force. So the universe gets smaller, smaller, smaller according to this Einstein’s equation.

But Einstein thought, “Oh, this is wrong,” because at that time, when Einstein came up with this equation, people believed the universe, it’s static, universe doesn’t change its size. It doesn’t get bigger or smaller, it’s always at the same time, so Einstein thought “This is wrong.” So to balance the gravity from the matter, Einstein added one additional term, called cosmological constant here. To balance the matter on matter’s gravity, he added this cosmological constant on the left side of the equation. Now the equation is stable, so universe doesn’t get shrink or expand by adding this. And then Einstein write a paper about this equation in this shape. However, in 1929, Edwin Hubble, this guy, discovered the expansion of the universe.

This is a figure from Hubble’s original paper and this is saying individual data points are galaxies and these, this figure is saying, more distant galaxies are moving away from us faster, so this is distance, there’s a velocity moving away from us, and as you can see more distant galaxies are moving away faster. What does this means? This is showing, this is the evidence of the expansion of the universe. Lemme demonstrate with this balloon. So, this balloon is a universe, and these individual points are galaxies. And if I expand this balloon. Uh, the expanding universe takes some energy, oh, the individual galaxies’ distances are getting larger and larger, you know, each distance is getting larger and larger.

And what you, I want you to see is, for example, starting from this galaxy, this galaxy is moving away, but this galaxy is also moving away, and this galaxy is also moving away from this galaxy. So compared to this galaxy, this galaxy, farther away, is moving away from our galaxy faster, so this is what’s happening, um, in Hubble’s law. So this is called Hubble’s Law. Okay. So, Einstein was pleased to hear about this Hubble’s discovery. He learned, universe can change the size, so, Einstein happily removed this cosmological constant, and then put the equa- Einstein’s equation back to the original form. Now the universe can change the form so the Einstein’s equation can be this original form.

And then Einstein called (cannot understand) cosmological constant was the biggest blunder in his life, his equation was correct in the original form. And how Einstein was so happy, so he personally visited Edwin Hubble in uh, Mt. Wilson observatory in California, to congratulate him in person, so this is Einstein, together with Hubble, looking into the Wilson, uh, Mt. Wilson observatory’s telescope. However, story doesn’t end here, this is the general story about Einstein’s biggest blunder, but recently there’s a continuing story here. Recently, people used super-nova explosions to map the expansion of the universe. So this is one example of super-nova explosion.

It’s so bright this is exploding one star, but it’s as bright as its own host galaxy, which, which holds ten billion stars inside. And what’s nice about this is, we know the brightness of this super-nova explosion, because it always explodes at the Chandrasekhar mass, the same mass, so brightness is more or less the same, and if you know the intrinsic brightness, then, we can measure the distance using super-nova explosion. If it looks like faint, then the super-nova is in a distant universe, if super-nova looks bright, it’s in a nearby universe. So these three gentlemen, measured the mapped expansion of the universe using this type of super-nova, and this is Hubble diagram, so distance against this is the brightness of super-nova.

And as you go far away, super-nova gets fainter, fainter, fainter. What was interesting here is those distant super-novas were little bit fainter than expected, so what’s expecting, expected is this dotted curve in the center, and then those data points a little bit above those curves. Why they’re a little bit fainter? Because, the expansion of the universe is not just the expansion— it’s expansion speed is accelerating. So these three people, by using super-nova found accelerating expansion of the universe. And that’s how, that’s why, these three gentlemen received the Nobel Prize in 2011. So, Einstein‘s equation was this form, and then Einstein removed this cosmological constant, calling it a biggest blunder, adding it as a biggest blunder.

But now, because the expansion of the universe is accelerating, we need this cosmological constant term again, not to balance the gravity from the matter, but to accelerate expansion of the universe. So that’s why, I guess, Einstein’s biggest blunder, to take this away was the blunder. So Einstein’s equation was correct, with cosmological constant. This is how Einstein was a genius, that’s an interesting story isn’t it? I stop here, see you next time, bye-bye.