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Physics, Astronomy & Cosmology / How many black holes are there in the Universe?

« on: 06/10/2018 23:27:57 »

There seems to be no controversy (in Science) with respect to the existence of the Black Hole. My question:

Is there more than one Black Hole in the Universe?

2

General Science / How is Question of the Week chosen?

« on: 06/10/2018 21:45:38 »

I can't figure out where to ask a question.

Will someone tell me where I can ask a question about one of the topic sub-sections?

"Hey, scherado, why don't you just ask the question?"

Alright, perhaps that's a good idea.

How is the "question of the week" chosen?

3

That CAN'T be true! / What size alphabet is required to name each non-negative integer?

« on: 19/02/2018 15:27:08 »

What size alphabet is required to name each non-negative integer?
You are advised in advance that the following is a trick question. It is, in full:

What size English alphabet is required to provide a unique name for each non-negative integer?

4

Physics, Astronomy & Cosmology / What does "time-like" mean in the following sentence?

« on: 17/10/2017 21:29:20 »

First point is that the term is an English translation of the original. From the Publisher's Note, page viii:

...
--The papers were originally published by the 
Querido Verlag in Amsterda. In fairness to Professor 
Einstein, his American publishers would like to make 
it clear that although they have his full authorization 
to translate the German text as published in Holland, 
and although the documents from which the original 
publication was made have his authentication, there 
has been no further collaboration by him.
...

The subject term is at the end of the passage quoted below.

From page 82 Essays in Science, essay Notes On The Origin Of The General Theory Of Relativity, by Albert Einstein, published 1934:

--A material point, which is acted on by no force, 
will be represented in four-dimensional space by a 
straight line, that is to say by a line that is as 
short as possible or more correctly, an extreme line. 
This concept presupposes that of the length of a linear 
element, that is to say, a metric. In the special theory 
of relativity, as Minkowski had shown, this metric was a 
quasi-Euclidean one, i.e., the square of the "length" ds 
of the linear element was a definite quadratic function 
of the differentials of the co-ordinates.
     If other co-ordinates arrew introduced by means of 
a non-linear transformation, ds² remains a homogeneous 
function of the differentials of the co-ordinates, but 
the co-efficients of this function (guv) cease to be 
constant and become certain functions of the co-ordinates. 
In mathematical terms this means that physical (four-dimensional) 
space has a Riemannian metric. The time-like extremal 
lines of this metric furnish the law of motion of a material 
point which is acted on by no force apart from the forces 
of gravity.

What is the meaning of "time-like?"