**Ask a monkey a physics question thread**

[MadMojoMonkey]

I mean the big bang sounds like a star imploding/exploding/whatever we call the creation of a black hole

... except that the Big Bang involves ALL of the stars, black holes and everything in the universe (even all the space and time) existing in a volume smaller than a single proton. There really is no comparison to any other kind of explosion or expansion.

A Black Hole is a region of space-time in which the gravitational energy well is too deep for anything to escape, even photons. Generally, they are formed by the core collapse of a massive star. Sometimes, 2 objects can collide to create a black hole. Also, an object that is nearly massive enough to be a black hole can become a black hole by accretion, the gradual gathering of mass from a nearby object.
There is also some evidence for primordial black holes, or black holes that formed in the early universe and were kind of the planted seeds for galaxies and eventually star formation.

So far, every galaxy observed (lol only 1, the Milky Way) has a super-massive black hole at its center.

and the universe expanding sounds like it fits the theory of a black hole sucking stuff in as it grows.

Black holes do not "suck stuff in as they grow"... except when they do, of course.

General Relativity tells us that mass curves space-time creating the illusion of a gravitational force. The force is an illusion, because objects move in straight lines at a constant velocity through curved space-time. Since only an object which is not being acted on by a force will move at a constant velocity in a straight line (Newton's 2nd), the "force" of gravity is an illusion cause by a human limitation in "seeing" the curvature of space-time.

E.g. if the sun were instaneously replaced with a black hole of equal mass, the planetary orbits would be unaffected.

All of that is to say, it is the mass of the object, and not its composition, that defines how much it sucks.

ALSO: Black Holes radiate profusely, by Hawking Radiation, which makes them not-so-black after all. It means they slowly shrink over time.
In other words, it really sucks to be inside them, and it kind of blows to be near them.

IF a black hole collides with a star or other massive object, then obviously, the resulting object is more massive than the original black hole, so it would have a "growth spurt" (I made that up). So, technically, they do "suck stuff in" and "grow" but it's not like they're the Hoovers of the universe.

Another point is that the black hole would be expanding because of "stuff" "coming in" from the "outside". Whereas, the universe is expanding because "space" is "spontaneously expanding" "everywhere".

This may be a dumb question as I know nothing on this subject whatsoever. But is there any evidence to suggest our universe is not the inside of a black hole. [...] Is this not the most obvious theory of our universe? Does anything prove/imply/suggest that this isn't the case?

There is just no basis for a physicist to answer this. Physics answers questions about observable things, and the inside of a black hole can not be observed by definition. So physics is simply not equipped to answer this as of now.

I mean... the way to answer it would be:
What are the implications/predictions of your theory?
Can any of those be measured?
If yes: Well, go on and measure that and see if the data support or refute your theory.
In no: Sorry, this is not science.

[Savy]

There is just no basis for a physicist to answer this. Physics answers questions about observable things, and the inside of a black hole can not be observed by definition. So physics is simply not equipped to answer this as of now.

I mean... the way to answer it would be:
What are the implications/predictions of your theory?
Can any of those be measured?
If yes: Well, go on and measure that and see if the data support or refute your theory.
In no: Sorry, this is not science.

There are definitely lots of top physicists trying to answer questions like this right now. Although they probably won't have any of their work verified in their life time. Always used to annoy me how people would just disregard the question "what was there before the big bang" because what we know as time didn't exist before the big bang, but that's not really what the question is asking and there are a few hypotheses about exactly this.

The question that used to piss me off was we'd get told "matter can't be created or destroyed", which leaves to the obvious question where did it come from then? Which I never really had answered by a teacher, when in reality this isn't the case and it's just a simplified theory of what is really happening which when I found out I didn't really understand why it couldn't be explained to a 14 year old.

[MadMojoMonkey]

Always used to annoy me how people would just disregard the question "what was there before the big bang" because what we know as time didn't exist before the big bang, but that's not really what the question is asking and there are a few hypotheses about exactly this.

The question, "What is beyond space-time?" is not a physics question... yet. Physics is interested in observable things, and since that kind of question is about something not-yet-observed, there is just no evidence to back any claims.

Still, there is good reason to ask the question and to postulate what might be, and follow through to see what the implications are.

The question that used to piss me off was we'd get told "matter can't be created or destroyed", which leaves to the obvious question where did it come from then? Which I never really had answered by a teacher, when in reality this isn't the case and it's just a simplified theory of what is really happening which when I found out I didn't really understand why it couldn't be explained to a 14 year old.

Well, Einstein explained that matter and energy are basically 2 sides of the same coin. Until then, the smartest people in the world believed that the Law of Conservation of Mass was correct. Most people even today don't have any clue what Einstein was talking about, so you can hardly blame your teachers... unless they were physics teachers.

The Law of Conservation of Energy still holds, though, once you accept that mass is a form of energy. The thing is that there is positive and negative energy, you see. The whole equation is really
E^2 = p^2c^2 + m^2c^4
where E is the energy, p is the vector momentum, c is the speed of light in vacuum, and m is the mass of the object.
This reduces to the familiar E = mc^2 when p=0.

Since p is the vector momentum, it can be positive or negative. E.g. 2 objects of identical mass moving away from a central point at the same speed have a net energy of 0.

So long as all the conservation laws are followed, all kinds of particles can pop into existence where there was "nothing" before. This is exactly what a particle accelerator experiment does. It smashes 2 protons into each other, annihilating them and producing a whole mess of particles that spray out. Two protons go in... hundreds or thousands of particles come out.

Check out this Encyclopedia Britannica article about Pair Production for a relatively simple explanation of 1 process by which energy becomes matter.

[a500lbgorilla]

Always used to annoy me how people would just disregard the question "what was there before the big bang" because what we know as time didn't exist before the big bang, but that's not really what the question is asking and there are a few hypotheses about exactly this.

What you should remember is that we're in the present, and we can only observe so far into the past. That limit is troublesome to the question you're looking to have answered. Stephen Hawking had a clever brush-away answer that he gave and people have always liked to shove at those who are getting ahead of themselves.

MMM, do you have a book/textbook suggestion for learning QM?

I tried getting into Feynmanns book, but I can't find any answer manual to go with his problem sets, so, it's a difficult time knowing I'm doing the math(s) right.

[Savy]

Quantum by Jim Al-Kahalili
http://www.amazon.co.uk/Quantum-Guid.../dp/1780223951

Meant to be quite good, more of a general overview though I think.

If you are looking to actually get your teeth sunk into it, "Principles Of Quantum Mechanics" by Shankar is a great book.

[MadMojoMonkey]

Interesting that you mentioned Jim Al-Khalili.

I was just looking for a good video to introduce the Double Slit Experiment, and this was what I found.

I encourage everyone reading the thread who is curious about Quantum Mechanics to watch this video and bring me your questions.