# Author Archives: bernander

## General Relativity (Level 2): Can you fall into a black hole?

These Level 2 videos analyze General Relativity topics that are a bit contentious. In this video, we ask, “With the speed of light going to zero at the event horizon, can you actually cross it?” The standard answer is often … Continue reading

## General Relativity part 6: Space expands

In six Level 1 videos we visualize General Relativity with a substratum (“fabric”). Here in part 6 of 6: Space expands in the Big Bang and inflation. Two horizons limit our visible universe to a small part of the whole. … Continue reading

## General Relativity part 5: Wormholes

In six Level 1 videos we visualize General Relativity with a substratum (“fabric”). Here in part 5 of 6: Wormholes are shortcuts through otherwise flat space. They can also act as time machines, if their mouths are properly attached to … Continue reading

## General Relativity part 4: Space moves

In six Level 1 videos we visualize General Relativity with a substratum (“fabric”). Here in part 4 of 6: Space moves, around a spinning black hole (Kerr spacetime). A spinning ZAM ring has zero angular momentum, and any motion relative … Continue reading

## General Relativity part 3: Slow light

In six Level 1 videos we visualize General Relativity with a substratum (“fabric”). Here in part 3 of 6: Locally, we always measure the speed of light to be 1. Over distance, we measure it to be less than one. … Continue reading

## General Relativity part 2: Curvature in 3 and 4 dimensions.

In six Level 1 videos we visualize General Relativity with a substratum (“fabric”). Here in part 2 of 6: We move on from 2d space to 3d space and 4d spacetime. In the Schwarzschild spacetime, we find that space contracts … Continue reading

## General Relativity part 1: What is curvature?

In six Level 1 videos we visualize General Relativity with a substratum (“fabric”). Here in part 1 of 6: What is curvature? In 2-d, we show curvature as either a deformation of pixels within the 2-d surface, or as a … Continue reading

## Special Relativity

This video reviews Special Relativity from the bottom-up viewpoint, in the spirit of John Bell. We start with the three phenomena – length contraction, time dilation, clock desynchronization – and then derive that c is measured to be constant, and that … Continue reading