Infinity and black holes?

Question

When you add infinity to infinity, why doesn't it get more than infinity? Ok, and black holes are real?! How do they work? And how many demensions are there? Does time count as one?

Answer 1

- Infinities
Suppose you have a hotel with an infinite number of rooms, numbered 1,2,3,... All rooms are occupied.
A tourist bus arrives, with an infinite number of passagers, who all want a room.
No problem. The hotel manager asks all people already in the hotel to move to the room, with twice the number they had before. 1 to 2, 2 to 4, 3 to 6, etc.
After some time all odd numbered rooms are empty, and the bus passengers all find a room.

- What are black holes?
A star is a big mass of gas. It originated as a hydrogen cloud that started contracting because gravity pulled it together. When this happens the interior gets denser and hotter. Dense enough and hot enough for fusion reactions to start. The latter produce heat and light that pushes outwards.

The result is an equilibrium between gravity and the light radiation. The star stabilizes and stays stable for billions of years. The sun is in this stage.

However, when the hydrogen is burnt up, the outward pressure is taken away and gravity takes over again. If the mass of this burnt out star is big enough, then there is nothing to counteract gravity.

The mass of the star will be more and more concentrated in a smaller and small volume. Gravity at the surface will become so strong that not even light can escape from it.

That is a black hole.

- Time is called a dimension because in Einstein's theory of relativity it makes mathematical sense to do so. Events happen in spacetime, 3 spatial and 1 time dimension. But their orientation in space and time relative to each other, depends on the observer and the relative speeds of the events.

In Einstein's formulas these dimensions are mixed by transformations depending on the velocities. This works only if we add time as a dimension.

- How many dimensions are there in our Universe?
We observe four dimensions everyday, three spatial and time.
But...theories such as string theory predict that the space we live in has in fact many more dimensions (frequently 10, 11 or 26), but that the universe measured along these additional dimensions is subatomic in size. As a result, we perceive only the three spatial dimensions that have macroscopic size.

This is not so strange as it sounds, which I'll show with an example. Imagine you are in an airplane, flying over sea. Seen from a height, the sea looks flat, two-dimensional. But when the plane looses height we start to perceive the waves, that move in a third direction we could not see before.

The universe could be the same. Four macroscopic dimensions and a few more, hidden ones. We can only perceive them for instance, by the small effects their existence might have on subatomic particles.

Answer 2

1) By definition, infinity can not be exceeded (i.e. infinity is all). - so it's same reason why adding 0 to 0 doesn't make more than 0.

2) Yes, they are real (gravity bends space & we can see this effect on the light from stars 'almost behind' the black hole)

3) Black holes 'work' by being so heavy/dense that gravity 'bends' space so much that everything that gets near falls into the black hole. Light from behine a black hole is bent towards it - light that gets too close falls in.

4) It is generally accepted that the normal equations of space/time break down at the center of a black hole. So it's not possible to say .

5) Yes - when describing the effect of a black hole on the rest of the universe, Time has to be included (time slows down due to bending of space & it is generally accepted that time = 0 at or near the center of a black hole)