Black Holes A black hole is a star that has collapsed to extreme density
Its gravity is so high that not even light can escape.
Why not?
In classical physics, the escape velocity (vesc) is the speed an object needs to leave the gravitational pull of something.
Set KE = PE & solve for vesc. ...
At some distance, (RS) from a BH, the escape velocity is larger than the speed of light: vesc =c . Event Horizon
...Is a sphere around a black hole whose radius is RSch It is a “point of no return.” Once inside, nothing can escape since vesc > c. Presumably, all mass is at the center, a point called a “Singularity”
So you could cross the Event horizon without even knowing it.
“Space is falling into the BH at the speed of light” Schwarzschild Radius
If a mass M is confined to a radius less then RSch it will become a black hole. Black Holes: Don’t Jump Into One!
If you fall into a Black Hole, you will have a big problem:
Your feet will be pulled with more gravity than your head.
You will be stretched out into “spaghetti”
………ouch! General Relativity
Karl Schwarzschild* (1873-1916) used the new General Theory of Relativity to determine RS (while fighting WWI)
General Relativity (GR) is Einstein’s replacement for Newton’s theory of gravity.
GR is an extension of Special Relativity (SR), which starts with a basic assumption:
“The laws of physics are the same for all observers.”
* Who came up with U,V&W velocities. Also, the father of Martin Schwarzchild, (see Crosswell p. 40 & p.99 ) Special Relativity (Ch. 4, C&O, not required) Einstein’s assumption that observers moving at any speed (v) measure the same speed of light implies two effects* :
Implications of SR: -moving clocks run slow -simultaneity is relative -space & time are a one entity: “spacetime” -mass is a form of energy: E=mc2
(*both part of the “Lorentz Transformations”) Relativity Tested
If space is curved, then light from a star, passing near the Sun, should be deflected.
But how could you see the star? ! A. Eddington observed a solar eclipse in 1919. ! Stars were found in slightly different positions. ! This confirmed that the Sun’s mass can warp space! Newton Was Wrong
Special Relativity has been confirmed many times (by Kennedy & Thorndike, 1932, by Stillwell & Ives 1938, and your GPS!)
But GR was confirmed first, in 1919. GR describes gravity as the curvature of spacetime, not a force. X
or
Curvature of space = amount of mass/energy Black Holes & Relativity ! Black holes also distort space and time tremendously. ! In 2016, “gravity waves” from 2 colliding black holes were measured by the LIGO instruments in Hanford, WA & Livingston, LA