For one, wouldn’t that mean they have a volume of zero? how does that work?
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They don’t. However, they have enough gravity to break the atomic bonds and pack sub-atomic particles even tighter together than any atomic-sized matter can get naturally. So in effect they are denser than any other measurable matter. And since sub-subatomic particles haven’t been discovered yet, it’s just called infinite to make it easier to visualize.
Singularity is a point (something zero-dimensional) with mass. Density is mass over volume. Dividing by zero results in infinity
When you describe a black hole (the kind of singularity you’re probably talking about) with our current theories (specifically general relativity), you arrive at the conclusion that they have zero volume, infinite density, etc.
But there is no experimental evidence for this, as we really can’t see what goes on inside a black hole.
We already know that general relativity is incomplete, failing to describe reality in certain situations. Ask a physicist who works with black holes and they’ll (probably) tell you that the singularity stuff is just another example of general relativity’s incompleteness.
A statement in physics about singularities is at least as much about saying “we don’t know what is happening” than about saying “this is what it is”.
A singularity is where the existing mathematical models of reality break down – they no longer work. Prior to achieving a singularity, the density is very high but a word like “density” cannot strictly be applied to a singularity although perhaps it could be the average density of a small region surrounding a singularity. (which would be high but not infinity)
Descriptors like “infinitely dense” are for the consumption of the non-physicists or descriptors to say “it is very very large”. It is semantic and metaphorical rather than precise.
It can’t. A singularity isn’t a real thing. A singularity is just a point where our physics stops working and we don’t know how to describe/model/predict what’s going on.
At a BB singularity, there are no “particles”. The energy density is too high for even subatomic particles to form. Remember, mass and energy are the same thing ( E = mC^2 ), so it’s really massenergy that’s too high for matter to exist. If you have energy, which doesn’t take up space, you can have an infinite amount in a region of zero volume.
Math.
Density = Mass / Volume
As the volumes reduces down to effectively zero (one Planck Volume, approx. 4.2E-105 cubic meters), any massive object’s density approaches infinity.
This makes a black hole, which by definition has collapsed down past that lower limit on volume, literally a Divide By Zero Error.
PS – Think of Planck Volume as Absolute Zero for size.
ELI5: Mathematically, that’s exactly what it is. A certain mass occupying zero volume, which means infinite density *by definition*.
Gravity still works because mass is still mass. Entire galaxies are still bound by and orbit around similar singularities (“supermassive compact objects”) in their centers.
Singularities haven’t been accepted as possible for about 40 years.
It’s now “believed” that where the maths predicts a singularity it’s the maths which is wrong/doesn’t account for actual reality.
A simple thought experiment to disprove a singularity is as follows.
If you take a singularity and double it in size how big is it?
It’s still a singularity.
So how many times would you have to double the size of a singularity to get the present size of the universe?
Infinite.
Can’t happen.
So basically any time a scientist mentions a singularity what they mean is that the incorrect theories/maths predict a singularity (and “unfortunately” these are currently our best theories) but in reality it would have some non zero size.
A “singularity”, in math, is a discontinuity. It’s a place where the math just doesn’t work–think, dividing by zero.
Presumably you’re talking about black holes. In that case, we can’t describe the singularity directly. Instead, we describe what happens as we *approach* the singularity. If you’ve ever taken any calculus, it’s just a limit–“what’s the behavior as we approach some value?” (EDIT: because I neglected to draw the connection. In the same way dividing by zero is a numerical discontinuity, a black hole singularity is a *topological* discontinuity. )
Our math does really well at explaining what happens almost arbitrarily close to the singularity, in the same way the math works as we divide by a number arbitrarily close to zero. But that specific point is indescribable with our current understanding.
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