Ask a Physicist

[Alja-Markir]

There is an edge to the "known" universe, although for humanity it is a pitiably small range of detection.

An edge to the universe? In the sense that the universe encompasses all, there isn't one. In the sense of vast tracks of empty space? Well, you'll find out in due time.

~Alja~

[BritchesStitches]

There is an edge to the known universe because we observe the universe through light. And if something is more lightyears away from us than however many years the universe has existed, it is impossible for the light from it to have reached us. However, that's a lot more simple to imagine than "what's beyond the universe?"

[Arius]

My guess: Bears.

---

There are two things I know I'll never be able to completely comprehend.

Infinity and nothing.

Infinity, just trying to imagine a continuous universe without any end. I can't really imagine it. At some point my mind tells me there has to be an end.

Nothing, a state of non-existence breaks my mind. When I try to think about it, I picture blackness. But, there wouldn't even be that. It just wouldn't be.

Anyway, I think for the purposes of this conversation, we should define universe as a collection of galaxies with the parent category being existence.

[theDreamer]

How is this for you:

The big bang was caused when all matter was in a singularity, and then that singularity started expanding, right?

(So I'm under the impression of. It wasn't large chunk of stuff A collides with likewise large chunk of stuff B, but rather large chunk of everything felt like expanding.)

A singularity is all of everything with nothing outside it.

There is nothing outside the universe.

The universe must be a singularity (this is not flawed logic, now is it?).

That seems a little...mind blowy to me. Maybe not to everyone.

[Master Gunner]

A singularity is not all of everything with nothing outside it. A black hole is a singularity, and we are certainly outside of it. A singularity is simply a point of infinite density, and as a result of that, the laws of physics as we understand them stop working.

[theDreamer]

Ah, see, I was mistaken then.

Laws of Physics do rarely work though...Thus ToE's issues...anyways...

[Arius]

What if we're not? What if it's all inverse?

If we accept the balloon explanation, what if black holes are reaching to the outside of the universe?

This could be the inside of a culmination of black holes.

[Master Gunner]

They work as a model of the universe within certain restrictions, we just have to fix the last gaps, or if that's impossible, come up with an entirely new model to deem "the laws of physics".

[Alja-Markir]

Black holes are just gravity wells.

They aren't magical portals to another dimension, nor are they gateways through time and space.

Flying into a black hole is pretty much exactly the same as flying into a star. The difference being that you would burn first in a star, and then be compacted into an incredibly dense mass, rather than the other way around.

The only reason people are mystified by black holes and not stars is that stars emit light, whereas black holes absorb it. Humans see this big blank spot and go, "Holy Shit! This thing is crazy! Not even light escapes it!" Well if the top layers of the sun were compacted into the core to a certain radius, all the light it produces wouldn't be visible at all either!

~Alja~

[BritchesStitches]

[Edit: Alja-Markir beat me to the black hole thing, but I'll leave what I said up]

eh... black holes are just really dense objects, most of the "special" attributes given to them are by scifi stories and such (not to say they don't have some pretty unique properties).

As for the earlier question of picturing "nothingness", we again fall back to observing things through the light they emit... and nothingness would emit no light, so yeah "picturing blackness" is accurate.

[Arius]

First, black holes are still highly theoretical. They're not even fully accepted in the scientific community.

I'm not saying they're some gateway, I'm just saying that we constantly think of black holes as something in the universe. But if we consider a universe that is finite, maybe they would be the edges.

[Master Gunner]

Black holes may still be theoretical, but the math and all of our observations fit that theory.

[Arius]

In as far as we know.

Gravity, theory. But provable.

Evolution, theory. But provable.

Ottawa, theory. But almost provable.

Black holes, theory. Completely unknown outside of observations of light and bodies. There's no real way to prove it yet.

[BritchesStitches]

I definitely would not call them "highly theoretical". While they physics that go on in a black hole might remain unclear, there have been many, many objects observed recently that are scientifically accepted as black holes.

[Arius]

I would, because gravity is theoretical and we know how it works. So, something we understand much much less about would be highly theoretical.

Don't take me as to saying they don't exist. I'm saying they are a theory that might have a different explanation than our current. That we don't understand it.

[Snowfire]

Can I just state, right here, that if you go with having gravity wells creating 'dimples' in the fabric of space then black holes (yes they're theoretical but they've been observed to the point where they or something like them has to exist) could conceivably be a form of transport conduit. There's only one problem. The massive jets of high energy radiation they throw out perpendicular to the disk of matter that can form around the singularity. Those things shape the movements of entire star clusters.

In all likelyhood, yes, black holes are just incredibly large (for a singularity) singularities. But the possibility of the combined gravity wells of two black holes 'connecting' (although I think this requires a limited universe) is there and we have absolutely no freakin clue what would happen if they did.

[epocalypse]

And now a break from intelligent convesation:

Black holes are cool!

Thank you, and resume.

[Lyinginbedmon]

If you consider wormholes a possibility, then black holes are good candidates for warping the fabric of space enough for them to be around in a decent scale.

Still, travelling near a black hole or through a worm hole presents a whole slew of very big problems that make neither tenable.

[Snowfire]

Well, there have been theories drawn up about how wormholes could exist. It's just finding observable evidence etc. And the there's this lovely idea called space folding...but that's sci-fi

Yes, there is a massive slew of problems with going in close to a black hole. But if you could somehow work out a way to survive the graviational stresses then all you'd need is some sort of protection from the jets of highly energetic and exotic matter I mentioned previously. Of course, if certain theoretical particles turn out to exist then that's no problem. That said, if said particles turn out to exist we probably won't need to care about black holes except as science projects.

[JesterJ.]

First, black holes are still highly theoretical. They're not even fully accepted in the scientific community.

"not even fully accepted" in the same way human impact on Global Warming is "not even fully accepted"
There is a ton of empirical evidence pointing towards the existence and function of huge, huge dense objects - they may just not exist exactly as Stephen Hawking predicts. For exactly that type of black hole, we cannot prove anything without actually seeing [impossible] or performing tests on a black hole. But we DO know that there are things out there that affect things in a way that can only be explained by a huge, huge mass, and we call that a black hole.

For example, there is time lapse footage - which escapes me at the moment - of three stars orbiting around each other in a pattern that is entirely unconventional: there seems to be something nearby the 3 stars that is pulling them and forcing them to orbit in a way that would not occur if it were just the 3 stars. We cannot see the thing that is affecting them, although we can see the stars. We know that it is this other thing, not the composition of the stars (some unusually dense material, etc.) that causes this uneven orbit, because we can tell by the...frequency(? wavelength?) of the emitted light from the stars that it is caused by...whatever material the stars are comprised of. And these stars are acting in a way that is unconventional to the way stars formed by this material should act.

TL;DR: We KNOW the way these 3 stars should be performing - there is no variable in them unknown, yet they do not perform how they should, unless there is a black hole present...in which case they are performing as they should.




(All of this is what my (admittedly very limited) knowledge of Astrophysics tells me...I may be wrong [especially about Hawking stuffs], please correct me if I am)

Another fun physics question: Imagine you are flying around in space in a spacecraft. PEW PEW! If you could calculate the orbit of planets around you, could you approach a planet to pick up velocity by way of gravity, then escape its pull as it orbits away? Think of it as sort of...skimming the gravitational pull of the planet.

I...can't really explain this very well without showing it via animation, but maybe that's clear enough for someone to understand.




I AM REALLY TIRED, THIS IS ALL RAMBLY. SORRY IF IT IS UNCLEAR. <3

[Arius]

I would, because gravity is theoretical and we know how it works. So, something we understand much much less about would be highly theoretical.

Don't take me as to saying they don't exist. I'm saying they are a theory that might have a different explanation than our current. That we don't understand it.

I just said that.

[Snowfire]

Another fun physics question: Imagine you are flying around in space in a spacecraft. PEW PEW! If you could calculate the orbit of planets around you, could you approach a planet to pick up velocity by way of gravity, then escape its pull as it orbits away? Think of it as sort of...skimming the gravitational pull of the planet.

I...can't really explain this very well without showing it via animation, but maybe that's clear enough for someone to understand.<3

Um...this sort of thing was used to accelerate the Voyager and Galileo space probes out towards their targets. It's commonly known as a gravitational slingshot.

[Arius]

Also, it got Tom Hanks back from the Moon.

That guy gets trapped far from home a lot.

[JesterJ.]

Another fun physics question: Imagine you are flying around in space in a spacecraft. PEW PEW! If you could calculate the orbit of planets around you, could you approach a planet to pick up velocity by way of gravity, then escape its pull as it orbits away? Think of it as sort of...skimming the gravitational pull of the planet.

I...can't really explain this very well without showing it via animation, but maybe that's clear enough for someone to understand.<3

Um...this sort of thing was used to accelerate the Voyager and Galileo space probes out towards their targets. It's commonly known as a gravitational slingshot.

Well then, I guess I'm a little late to the game. Thanks.

[Lord Chrusher]

For example, there is time lapse footage - which escapes me at the moment

Here is such a video with some explanation by the Germans who made the observations.

First, black holes are still highly theoretical. They're not even fully accepted in the scientific community.

"not even fully accepted" in the same way human impact on Global Warming is "not even fully accepted"
There is a ton of empirical evidence pointing towards the existence and function of huge, huge dense objects - they may just not exist exactly as Stephen Hawking predicts.

The evidence for black holes is much stronger than the evidence for human caused climate change. JesterJ is right - we know that there are objects so massive and dense that not even light can escape. However we can currently only theorize about about things like Hawking radiation and what goes on inside the event horizon, especially close to the center.

The has been some talk about singularities in this thread. A singularity occurs in general relativity at the center of a black hole as the density goes to infinity and blows up which is usually a sign that your theory is wrong. Intense gravity at small scales is in the realm of quantum gravity, something despite what some string theorists may tell you we do not have a satisfactory theory for. The existence of a singularity with in a black hole may be the result of using general relativity outside of its area of applicability. The same goes for a singularity at the start of the big bang. Observation tells us that the universe was once very hot and very dense. If we apply general relativity to this and extrapolate backwards we get the entire universe compacted into a point at t = 0. However at some point the universe was so dense that quantum gravitational effects would have predominated so general relativity is no longer useful. Since general relativity is an incapable of correctly describing what occurs at the centers of black holes and at the start of the big bang does not mean it is wrong; any more complete theory will have to replicate all the larger scale predictions of general relative much like Newtonian gravity is the low density limit of general relativity.