Consider a one dimension example where you are flying away from the Earth in a big spaceship at velocity v as measured from Earth. You then fire an escape pod (in the same direction you are traveling) at velocity w’ (its velocity with respect to the big spaceship).
Given values of v and w’; we might want to know what the people on Earth will measure as the velocity of the escape pod. This is w (the velocity of the Escape pod from the Earth’s perspective).
If anyone is interested in trying it, I recommend using light seconds per second as a unit for your velocities. This will force c^2 = 1; making calculations much simpler. Make sure you express v and w’ as a fraction of the speed of light. So if the big ship is moving at 50% of light speed (with respect to the Earth) that would be v = 0.5
Yes but at least this comes from what we are able to observe of the universe. The universe was once thought of as infinite but science and observation show us it is approximately 92 billion light years across. And it is still expanding so one day that distance will be expanded as well. Imagine a few million years from now, it will probably be over 100 billion light years across.
Science is what tells us the universe if flat, so I go with that. At least until science makes new discoveries.
