At present the Corona crisis is very severe. Many people die from the virus. The damage to the economy is huge. Nonetheless, I want to write on another problem of mankind, the climate change. I have read a German book on this subject by two climatologists from Potsdam, Rahmstorf and Schellnhuber. They report on a large consensus in science that the global warming is caused by man. Doubling the amount of carbon-dioxide in the atmosphere would mean a temperature rise of 3 Kelvin (+/- 1 K at a confidence level of 95%.) Those who want to know more are advised to read the reports of the IPCC (Intergovernmental Panel on Climate Change.) I think their scientific arguments should be taken seriously, as well as their concern to use the knowledge of our time in a responsible way.
Recently scientists succeeded in taking a picture of a black hole. Therefore, I want to write a few lines about this phenomenon.
In a black hole, matter is so highly compressed that even light cannot escape from its vicinity. General relativity treats a black hole as a point, i.e. it has no extension. This is hard to imagine. However, take as an example the electron which is considered as a point particle, although it has a mass at rest.
A black hole is surrounded by an event horizon. Everything that passes it becomes invisible for the world outside. If a matter-antimatter pair is created from the vacuum near the event horizon, a particle may cross it. The other particle seems to come out. This is Hawking radiation.
In particle physics, there are collisions at high energies. Can a black hole be produced in a collider experiment? This question was subject of a court dispute. The physicists bring forward the argument that the cosmic radiation contains particles of much higher energy. Although the cosmic radiation hits the Earth, our world still exists.