Lecture 5 | Topics in String Theory

[grunder20]

what does STRING THEORY really mean?

[agapitoflores001]

I'd continue liking StanfordUniversity videos. They are very educational. In fact I have watched hundreds of their videos.

[Throred]

Thx stanford.

[badblueman]

45:50 The light emmited from the inner-guy just before the black hole is formed would have no problem outrunning the growing event horizon since both travel at c. No?

That's what I meant that the outer-guy would see the inner-guy get swallowed and not his grandfather-particles.

[badblueman]

I don't understand. Look at 0:47:20 for example. My question is, and I'm probably wrong, but if the red and green lines represent the speed of light, why does the event horizon form in 0 seconds? Doesn't the gravitational field spread at the speed of light? Why isn't the squiggly line at the same angle as the red line?

0:45:00 It's my understanding that the guy standing outside the event horizon-danger zone, would in fact see the inner-guy get swallowed, not his grandfather.

Please correct me.

[luzzie9]

@badblueman The red line is the collapsing shell of light. The green line is just the dividing line

between what can and what cannot escape. The event horizon is formed as soon as you create the shell of light which may take some time. As the shell collapses, the event horizon follows it in. The squigly line is the singularity which does not move.

[badblueman]

@luzzie9 But according to the graph, (time/radius) the slope represents speed. A collapsing shell - the red,green line and it's slope represents the speed of light...nothing in the universe goes faster than the speed of light. But apparently, according to the graph (as I see it) , it shows that gravity travels faster than the speed of light. Follow with your finger what happens when the r of the shell is 0. The gravity increases at the speed of infinity. The EH reaches a big r in 0 seconds.

[luzzie9]

@badblueman The only thing moving on that graph is the collapsing shell. The green line is imaginary in that you would not see or feel anything as you crossed it. As soon as you assemble the light shell it creates the gravitational field around it. As it begins to collapse, the gravitational field around it remains and does not move, but it does grow stronger as the shell collapses towards a more condensed state. Even after the shell reaches singularity the gravitational field remains.

[badblueman]

@luzzie9 Ohhh, so what you're saying is that the light shell starts creating a gravitational field before it collapses completely...things start making a whole lot more sense to me. I'm a complete amateur of course, for some reason I just assumed that gravity would emerge only after the shell collapsed. I watched again and got it this time.

Thank you very much for your time and patience! Can't believe I missed all that.

[nickharvey7]

Could quantum mechanics represent the passage or Arrow of Time?

This theory is based on just two postulates,

1.The first is that the quantum wave particle function explained by Schrödinger’s wave equation represents the forward passage of time or Arrow of Time itself photon by photon, quanta by quanta or moment by moment.

2. The second is that Heisenberg’s Uncertainty Principle that is formed by the wave function is the same uncertainty we have with any future event.

No strings!

[abuhajara]

wow.

Good stuff.