**Ask a monkey a physics question thread**

[MadMojoMonkey]

Back to physics...

http://www.bbc.co.uk/news/science-environment-39642992

What the actual fuck is negative mass? I've come to understand mass as resistance to acceleration. The "heavier" something is, the more resistance it has. Something with zero mass, ie a photon, has no mass because it has no resistance to acceleration... it always moves at c, so does not experience a change in state of motion, thus, no mass.

So how can negative mass be explained in inertial terms?

lol
"not the apparatus used in the latest research"
Editor was all, "I don't care. Put a sciency picture on this article, dammit!"

***
They're saying that it's the inertial mass that is negative (no mention of gravitational mass). They're not saying any known laws of physics need revision.
So F = ma, still. (bold letters used to indicate vectors)
F doesn't change, a doesn't change, only the sign of m changes. The result is that the applied force causes acceleration in the opposite direction of the force.
Meaning that if I push something with negative mass, it will move toward me, not away from me, as expected.

They're not saying any single particle behaves this way. They're saying there is a region of the Bose-Einstion Condensate which behaves in this way.
It sounds like it's a property of the system, and not of the particles.

This still needs peer review and replication as far as I can tell.

[OngBonga]

They're saying there is a region of the Bose-Einstion Condensate which behaves in this way.

Hmm ok well my very limited knowledge of this stuff is that it flows without losing energy, so I guess there's certainly going to be unusual currents.

I'll wait for that peer review before wasting valuable stonedness on this matter.

[OngBonga]

They're saying that it's the inertial mass that is negative (no mention of gravitational mass).

Well they're the same so if one is negative so is the other. Isn't it intuitive why they're the same? Inertial mass is resistance to acceleration... force acceleration mass thingy... well that what's happening in a gravity field... gravity provides the force, the ground causes acceleration in the form of constant change of velocity (constantly stopping you falling at terminal velocity), so gravitational mass is the resistance that stuff has to this acceleration. How has this not been resolved like 70 odd years ago? Why is something that causes brilliant people headaches so obvious to me? Is my weed really that good or am I missing something?

[MadMojoMonkey]

The theories we use to describe these forces are dramatically different, though.

All other forces are understood as the exchange of quantum particles.

Gravity is understood as curvature of spacetime.

There is no a priori reason things with disparate explanations should have similar effects.

I don't know anyone who doesn't agree with you that it seems obvious, but the logical ideas (math) uniting QM and GR are as of yet still unknown.

[OngBonga]

All other forces are understood as the exchange of quantum particles.

Oh ok, I see where the problem is. Ok, this quoted bit is probably wrong. The other forces are also curved spacetime, just much more profound, and much more localised.

Solved.

[Keith]

I'm sure I said somewhere that my comp room has no windows. Where the AC unit going?



That's gonna happen this year anyway.



I'm going with houseplants first, remember? I don't think my friends will find anything unusual about that. Even so, I'm not in any hurry to invite guests into my warm humid comp room with one seat so we can watch porn together.

I'm guessing the sale of the "houseplants"grown in the warm humid room with no windows will be financing the new computer

[OngBonga]

haha I wish. If it were financing anything, it'd be an AC unit first and foremost.

Be suspicious when I pretend I've got a job.

[a500lbgorilla]

Just for fun, how do rockets fly?

like this:

http://i.imgur.com/6qhtZa1.gifv

[MadMojoMonkey]

Nice

[CoccoBill]

MMM, if you could get the answer to one scientific question, free of charge, what would that be?

Oh and thanks for your answer to my previous Q, I'm still digesting it. Great stuff.

[BananaStand]

MMM, if you could get the answer to one scientific question, free of charge, what would that be?

I'll bet it's black-hole related

[MadMojoMonkey]

MMM, if you could get the answer to one scientific question, free of charge, what would that be?

I'm guessing you mean something like, "What, in my opinion, would be the most revealing question in physics to know the answer to?"

What is the theoretical link between QM and GR?

***
There's a wiki page on unresolved problems in physics. It's not a short page.

Oh and thanks for your answer to my previous Q, I'm still digesting it. Great stuff.

I'll bet it's black-hole related

Yep.

[MadMojoMonkey]

Whaaaaaaaaaaat...?

What is this "time crystal" thing you made?

http://www.livescience.com/58171-tim...n-the-lab.html

I'm just gonna put a pre-emptive set of:
IDK
IDK
IDK
IDK

for your coming questions.

(I may be able to answer some stuff, but the specifics are lost on me.)

[Savy]

I'm guessing you mean something like, "What, in my opinion, would be the most revealing question in physics to know the answer to?"

What is the theoretical link between QM and GR?

You'd choose that over fusion?

[MadMojoMonkey]

You'd choose that over fusion?

What about fusion?

What specific question do you think I'm missing?

[OngBonga]

There's a wiki page on unresolved problems in physics. It's not a short page.

I'm on it. Might take an hour or two.

[CoccoBill]

What is the theoretical link between QM and GR?

Ok, yeah I guess a unified theory would be a big one. I'd have started with either "what causes gravity" or "what caused the big bang" or something. I'd assume we'd get a better idea of those too with a unified theory.

[CoccoBill]

What about fusion?

What specific question do you think I'm missing?

Ooh I know this! Fusion is easy, in theory. It's cold fusion that's slightly problematic.

[Savy]

What about fusion?

What specific question do you think I'm missing?

Getting it to work so that it basically solves energy.

[OngBonga]

what causes gravity

He can just ask me that, and then correct me when I get it slightly wrong.

[OngBonga]

It's cold fusion that's slightly problematic.

And by slightly you mean extremely?

[OngBonga]

Getting it to work so that it basically solves energy.

I would've thought that if he can unify GR and QM then he would solve the energy problem.

[OngBonga]

If I could have the answer to a phsyics question, it's how can I turn dust into weed.

[MadMojoMonkey]

Getting it to work so that it basically solves energy.

Fission kinda already solves this. The problems with fission come down to science communication, not physics.

If someone can convince the public that nuclear power is ridiculously much safer than burning coal / oil, with lower impact on the environment, then power problems are solved for decades.

If I could have the answer to a phsyics question, it's how can I turn dust into weed.

IDK
Have you tried planting a seed in it?

***
Does this count as "aiding and abetting?"

[MadMojoMonkey]

Ok, yeah I guess a unified theory would be a big one. I'd have started with either "what causes gravity" or "what caused the big bang" or something. I'd assume we'd get a better idea of those too with a unified theory.

I'm not sure if these are science questions.

Science can only describe and predict "what" happens. It has nothing to say on the matter of "why" anything happens.

[OngBonga]

Have you tried planting a seed in it?

No, to be honest I never considered using dust as a growing medium. I'm unconvinced that dust has good enough hydro retention to do the job.

I guess it does depend on the nature of the dust in question, though most of the dust in my house is ash.

Does this count as "aiding and abetting?"

Nah. We're pretty slack in that respect. Seeds aren't illegal. So I could sell seeds to someone and not break the law, even if they tell me they intend to plant it, grow it and smoke it.

[MadMojoMonkey]

No, to be honest I never considered using dust as a growing medium. I'm unconvinced that dust has good enough hydro retention to do the job.

I guess it does depend on the nature of the dust in question, though most of the dust in my house is ash.

Not to spoil your fantasy, but...

The vast majority of dust in your house is human skin cells, the mites that eat human skin cells and those mites' excretions.

[Savy]

Fission kinda already solves this. The problems with fission come down to science communication, not physics.

If someone can convince the public that nuclear power is ridiculously much safer than burning coal / oil, with lower impact on the environment, then power problems are solved for decades.

It's a whole different level though and it's without all the bullshit that comes with fission.

[Poopadoop]

The vast majority of dust in your house is human skin cells, the mites that eat human skin cells and those mites' excretions.

Ah, no that's a myth. Dust is mostly made up of dust.

Search Results
Dust in homes, offices, and other human environments contains small amounts of plant pollen, human and animal hairs, textile fibers, paper fibers, minerals from outdoor soil, human skin cells, burnt meteorite particles, and many other materials which may be found in the local environment.

[CoccoBill]

I'm not sure if these are science questions.

Science can only describe and predict "what" happens. It has nothing to say on the matter of "why" anything happens.

Oh I totally meant "what" caused, not "why" in any puny-human-mind-seeking-meaning-and-purpose sense.

More in the vain of

Why does my room light up when I turn the switch?
Electricity is released on the bulb causing it to heat up and release energy in the form of visible light.
Why does the switch release electricity?
We have power plants creating it from coal, nuclear, solar, wind etc. and wires to connect it to your switch.
Why do those things have energy potential?
The sun is a huge ball of hydrogen and helium fusing due to gravity and makes all those things possible. Well, all our energy forms except for tidal and geothermal.
Why is the sun a huge ball of fusion energy?
Gravity.
Why is there gravity?
Cos something somehow bends space-time...? Fuck if I know.

On second though, this should probably be in the drunk thread.

[MadMojoMonkey]

Oh I totally meant "what" caused, not "why" in any puny-human-mind-seeking-meaning-and-purpose sense.

I wasn't sure. It seemed like I could have interpreted the questions either way.

The reason that I prefer my question is that your questions could have short answers which don't help me understand anything.

"What causes gravity?"
Flarvurum.

"What caused the Big Bang?"
A Flarvurum deficiency in the zilnoform continuum, LDO.

My question: "What is the theoretical link between QM and GR?" needs a whole theory to be explained in order to count as an answer.

On second though, this should probably be in the drunk thread.

[OngBonga]

Not to spoil your fantasy, but...

The vast majority of dust in your house is human skin cells, the mites that eat human skin cells and those mites' excretions.

Is it rich in magnesium and calcium?

[Poopadoop]

Is it rich in magnesium and calcium?

1. He said skin, not bones.

2. Skin cells are not what dust is mostly made up of.

[MadMojoMonkey]

@ong: No. Skin is not rich in either magnesium or calcium. That's what fertilizer is for.

@poop: I concede that neither of us is definitively correct on the question of "what is dust?"

A) There are a ton of conflicting sources, and even the quotes I can find by "experts" on dust lack any links to their studies and data.

B) Dust is a definition of particulate size. Any object or substance which is of that physical size is considered dust.
Therefore, the composition of dust varies widely from location to location.
(Dust at a smelter is going to be dramatically different than dust in a house.)

C) Dust from textiles and hair tends to be fluffy, or lower density than skin dust. Dust from human skin cells and the dust mites that eat them tend to be compact, and have a higher density.
The ratio of what is most prevalent will be different if you're comparing amounts by volume or amounts by mass.
The sources I've found do not state which metric they've used to draw their conclusions.

[Poopadoop]

@poop: I concede that neither of us is definitively correct on the question of "what is dust?"

Don't concede anything on my behalf lol.

A) There are a ton of conflicting sources, and even the quotes I can find by "experts" on dust lack any links to their studies and data.

B) Dust is a definition of particulate size. Any object or substance which is of that physical size is considered dust.
Therefore, the composition of dust varies widely from location to location.
(Dust at a smelter is going to be dramatically different than dust in a house.)

C) Dust from textiles and hair tends to be fluffy, or lower density than skin dust. Dust from human skin cells and the dust mites that eat them tend to be compact, and have a higher density.
The ratio of what is most prevalent will be different if you're comparing amounts by volume or amounts by mass.
The sources I've found do not state which metric they've used to draw their conclusions.

One thing that seems clear is that there isn't sufficient volume or mass of shed skin cells to make up the majority of house dust. An empty house collects dust, for example, though there's obviously no human skin cells being shed in it. I'm inclined to think house dust is mostly mineral matter (i.e., dirt) and plant matter (e.g., pollen), with animal matter coming in a distant third behind those two.

[OngBonga]

@ong: No. Skin is not rich in either magnesium or calcium. That's what fertilizer is for.

I think if I'm gonna plant a seed, I'll find a better medium than fertilised dead skin cells.

[MadMojoMonkey]

Don't concede anything on my behalf lol.

That's fair.
I didn't mean to.

Oops.

One thing that seems clear is that there isn't sufficient volume or mass of shed skin cells to make up the majority of house dust.

Upon what data is this assertion based? I looked for any data to affirm or refute this claim and I found none.

An empty house collects dust, for example, though there's obviously no human skin cells being shed in it.

This is already addressed by my point (B) above.

I'm inclined to think house dust is mostly mineral matter (i.e., dirt) and plant matter (e.g., pollen), with animal matter coming in a distant third behind those two.

If you're not willing or able to present data on this, then you're welcome to start the "Things Poopadoop is inclined to think, despite the dearth of evidence" thread.

[Poopadoop]

If you're not willing or able to present data on this, then you're welcome to start the "Things Poopadoop is inclined to think, despite the dearth of evidence" thread.

How about "Things that appear to be common sense" thread?

Your outer layer of skin regenerates once every 35 days. Take that amount of dead skin cells, multiply it by the number of people in the house, subtract a big chunk for the skin that gets sloughed off while people are outside the house and/or washed down the shower/sink drain, then divide that by the surface area of everything in the house, including carpets, tables, etc.. How thick a layer of dust do you think that would make?

Maybe you should start a "Things you heard somewhere and thought sounded cool so you repeated them as though they were facts, and then got argumentative when someone pointed out they were bullshit" thread.

[MadMojoMonkey]

How about "Things that appear to be common sense" thread?

That'd be fine, too.

Your outer layer of skin regenerates once every 35 days. Take that amount of dead skin cells, multiply it by the number of people in the house, subtract a big chunk for the skin that gets sloughed off while people are outside the house and/or washed down the shower/sink drain, then divide that by the surface area of everything in the house, including carpets, tables, etc.. How thick a layer of dust do you think that would make?

I'm not saying you're wrong. I'm saying I can't find any data which backs up your claim.
I'm saying if you can't or don't want to find any data which supports your position, either, then this is the wrong thread.

Maybe you should start a "Things you heard somewhere and thought sounded cool so you repeated them as though they were facts, and then got argumentative when someone pointed out they were bullshit" thread.

I didn't say it because it sounds cool. I said it because my best friend for 30 years wrote a paper on dust (admittedly, in high school), and he told me the thing about skin cells. It seemed like a reliable enough source at the time. It wasn't until you questioned it that I ever heard contrary.

I took your position to heart and embraced skepticism about my own position. I looked for relevant data or evidence to elucidate the situation. I found inconclusive statements from "experts" and contradictory statements between different articles.

I'm not arguing with you. I'm saying I can't find evidence to definitively support either of our positions.
If anything, I'm disagreeing with your position as definitive, and I've stated 3 reasons for my skepticism.

[Poopadoop]

I don't need scientific data to tell me when things clearly don't add up - that's why i have common sense. And common sense tells me I'm a lot smaller than my house and there's no way I could shed enough skin to create a visible layer of dust over the entire house every few days.

But if you're still not convinced, then let's do the maths.

A layer of skin varies from 0.5 to 1.5 mm thick, depending on where on the body you measure it. The average person has 1.5-2.0 m surface area of skin. The average house has maybe 100 m2 of floor space.

0.001 m layer of skin * 1.75 m2 surface area of skin on the body = 0.00175 m2 of skin cells shed every 35 days by the average person. Assuming 3 people live in the house and never leave the house or wash themselves that makes 3* 0.0175 = 0.00525 m2 of skin cells.

Now spread that out over 100 m2 of floor space- we'll just ignore the furniture and whatnot for the sake or argument. That's a layer of skin 0.0525 mm thick that would accumulate over 35 days, not enough to even see with the naked eye. I see dust visibly accumulating in my house a few days after dusting. It also accumulates when I'm away from the house for a few days.

Ergo, the skin cells theory of dust is as retarded as it sounds.

[MadMojoMonkey]

A hypothesis!

Now test it, and share your results!

***
I don't get why you're so feisty on this issue.

Clearly, dust accumulates where people are not... as dust is a measure of particulate size, nothing to do with humans.
We're not talking about dust in random non-occupied places, though. We're talking about homes in use by people.

All I'm saying is that it's plausible to me that in some houses there are significant human skin cells, dust mites, and mite excrement in the dust to account for a majority of the mass of dust.

Your assertion that this is never the case is strongly worded and requires a strong demonstration of fact to change my mind.

If your sense is so common, it should be easy to conclusively demonstrate your assertion.

[BananaStand]

Your assertion that this is never the case is strongly worded and requires a strong demonstration of fact to change my mind.

Dude...he showed you the math.

Plus he severely lowballed the average house size at 100 m2.

[Poopadoop]

If your sense is so common,

Not as common as I thought, apparently.

it should be easy to conclusively demonstrate your assertion.

It was, did you not read it?

[Savy]

What about a really tall and fat person in a really small room? Does it help if they have certain skin conditions?

I need to see some formulas, repeatable experiments, etc.

[Poopadoop]

What about a really tall and fat person in a really small room? Does it help if they have certain skin conditions?

I need to see some formulas, repeatable experiments, etc.

A tall fat person with psoriasis who lives in a tiny room is something I hadn't considered, I admit.

[BananaStand]

So many HVAC related variables to consider.....

[MadMojoMonkey]

Not as common as I thought, apparently.

This is the reason we need science to root out what "seems" legit from what "is" legit.

"Armchair philosophy" is fine for moral and ethical discussions, but it fails when it comes to making measurable predictions about the world.

It was, did you not read it?

Your statement of plausibility is fine, but it is not a proof, no matter how "reasonable" it sounds.

My critiques:
You've approximated the amount of some human skin dust which you expect in some situations, not all dust in all situations.
You've ignored the amount of dust which is mites and the mites' excrement.
You have not compared those amounts of dust to amounts of dust from other sources.
You have not demonstrated the comparative mass of these sources, as your analysis is based on surface area.
You have not made it clear whether or not you include elements like hair and other macroscopic particles which are commonly mixed in with the household dust, and which I would be hard pressed in a less formal discussion to disagree that stuff is dust.

In short, you've made an argument that human skin is not all of the dust, but you haven't given any context over how much of the dust it is.
Your calculations seem reasonable, but need to now be buoyed by data to support your assumptions.

[Poopadoop]

"Armchair philosophy" is fine for moral and ethical discussions, but it fails when it comes to making measurable predictions about the world.

Agreed. That's why I did the math just to show how absurd it was.

Your calculations seem reasonable, but need to now be buoyed by data to support your assumptions.

I'll get right on that. First I gotta find me a giant ruler to get some hard data on the distance to the sun.

[OngBonga]

I'll get right on that. First I gotta find me a giant ruler to get some hard data on the distance to the sun.

Assuming you could even create a big enough ruler (you can't), a ruler is going to be a really poor method of accurately measuring such large distances. For a start, you'd need to ensure it is perfectly perpendicular to the earth, and that there is no flexing. Also, you're going to have to find a material that is capable of withstanding what I would imagine are immense pressures at the earth end, and definitely at the sun's end. Also, it needs to not expand as temperature increases. Furthermore, you need to accurately measure it and mark it before you can use it. Factor in the time it takes to make the measurement, coupled with the distance between the earth and the sun constantly changing, and I'd say the time you should waste thinking about making a giant ruler should be equal to the time I've wasted making this post.

[CoccoBill]

Or you could use a radar to measure how far venus is and then

[Poopadoop]

Making the giant ruler is what techies are for. I'm just the brains behind the operation, the visionary if you will.

[Poopadoop]

Or you could use a radar to measure how far venus is and then

Nah, not scientific enough because it involves math.

[Poopadoop]

Assuming you could even create a big enough ruler (you can't)

This is why you'll never be my techie. I don't want to hear words like 'can't'.

[MadMojoMonkey]

Agreed. That's why I did the math just to show how absurd it was.

If that's why you did the math, you missed the mark for the reasons which I offered in my critique above.

I thought you were a real-life, published scientist?
What publication would post your above "proof" as science?

I'll get right on that. First I gotta find me a giant ruler to get some hard data on the distance to the sun.

There are plenty of credible sources which contain that datum, but I firmly embrace your DIY spirit of attempting to affirm or refute it with your own experiments.

Keep us posted on your 93 million-mile-long ruler project. I'm quite interested in the engineering challenges you have to overcome to maintain rigidity over such length scales.

[Poopadoop]

If that's why you did the math, you missed the mark for the reasons which I offered in my critique above.

Your 'critique' was specious and not worth rebutting in my opinion. Try making a reasonable argument if you want to be taken seriously as a dust analyzer.

I thought you were a real-life, published scientist?

According to some people I am both real life and a published scientist.

What publication would post your above "proof" as science?

I suppose either the Journal of Dust or the Journal of Epidermal Studies would be interested, if not Nature. I'll let you know where it ends up so you can submit something for the comments section.

Keep us posted on your 93 million-mile-long ruler project.

I believe Ong is working on that as we speak, though if I don't see a change in his 'can't be done' attitude the job may be opening up soon.

I'm quite interested in the engineering challenges you have to overcome to maintain rigidity over such length scales.

All the women in my life can attest to my ability to maintain rigidity.

[Savy]

A tall fat person with psoriasis who lives in a tiny room is something I hadn't considered, I admit.

At what point do bits of skin become dust rather than chunks of skin? That's important too.

[MadMojoMonkey]

Your 'critique' was specious and not worth rebutting in my opinion. Try making a reasonable argument if you want to be taken seriously as a dust analyzer.

My critique touches on many points. Any one of them is reason to be skeptical of your assertion.

Try making an evidence-based claim if you want to continue this conversation as a scientist.

Since it's clear that you don't, though...

According to some people I am both real life and a published scientist.

I suppose either the Journal of Dust or the Journal of Epidermal Studies would be interested, if not Nature. I'll let you know where it ends up so you can submit something for the comments section.

I believe Ong is working on that as we speak, though if I don't see a change in his 'can't be done' attitude the job may be opening up soon.

All the women in my life can attest to my ability to maintain rigidity.

[Savy]

I don't get why you've got your panties in a twist over this, it seems fairly clear from the information Poop gave that although dust does have skin in it it's going to be a smallish amount.

I'm sure there will be parts of houses that people live in which have more human skin than others that people spend a lot of time in such as beds but even then it's probably not all that much of what dust is overall. If the main place that people are brushing off dead skin is in the shower you'd imagine most of it gets washed away anyway.

I agree that none of this is rigorous but your claim isn't either and what has been spoken about certainly points in Poops direction.

All that being said it certainly shouldn't be in this thread.

[OngBonga]

I believe Ong is working on that as we speak, though if I don't see a change in his 'can't be done' attitude the job may be opening up soon.

Yeah so far I've made three spliffs and four cups of tea. Getting there, slowly.

[Poopadoop]

Yeah so far I've made three spliffs and four cups of tea. Getting there, slowly.

That's good work. Keep it up and I'll put you in charge of my ladder to the moon project.

[BananaStand]

Do I understand correctly that the Universe is expanding in all directions?

If so, how do we reconcile that with the existence of super massive black holes? The milky way is getting sucked into one right now, is it not? Eventually this galaxy, and all the galaxies around us will be sucked into this thing , correct?

So how can the universe be expanding if there are black holes floating out there condensing entire galaxies into super dense masses?

[MadMojoMonkey]

Do I understand correctly that the Universe is expanding in all directions?

Yes.
It is also interesting to note that it is accelerating in the expansion, which is, as of yet, not explained by physics.

If so, how do we reconcile that with the existence of super massive black holes?

These 2 things are unrelated.
A) SMBH's were formed in the very early universe. For some unknown reason, the cosmic soup that was the big bang was not homogeneous in its density distribution. The variations in density gave rise to the coalescence of matter into some regions and not so much others. Black holes have been present since basically forever.

B) The universal expansion happens at all points in space. The space in between the black holes is expanding. If there is enough distance between a pair of black holes, then the universal acceleration driving them apart is greater than the gravitational acceleration pulling them together.

The expansion of the universe happens over vast distance scales. The Milky Way, our Local Group of galaxies and the greater supercluster of galaxies in which the Milky Way exists are more strongly gravitationally bound than the current rate of acceleration of the universe will affect.

In this respect, the SMBH's are counteracting the universal acceleration within this domain.

The milky way is getting sucked into one right now, is it not?

It is not. The galaxy is in orbit about Sagittarius A* (the SMBH in the Milky Way), much the same that the planets are in orbit about the sun.

Black holes are a gravity source like any other unless you're "near" the event horizon.

Left alone, black holes are theorized to slowly evaporate in a process known as Hawking Radiation, named after Stephen Hawking, who discovered the physical-mathematical framework which implies this.

Black holes only suck things up when those things get flung into one of their event horizons. The swirling mass of stars that form the Milky Way occasionally leads to near collisions of stars. When stars pass too close to each other, there is a transfer of gravitational energy. This can leave one of the objects with an orbital velocity that is too slow to avoid the galactic nucleus. If so, that object is heading toward the black hole and will get consumed by it.

Merely getting flung "close" to the black hole may be enough, since most black holes have an accretion disk, or a disk of swirling, in-falling material. If a body enters that stuff, there is plenty of friction there to further reduce its orbital velocity and send it into the black hole... well... it'll likely get torn to bits and remain in the accretion disk for quite a while as it is consumed.

Eventually this galaxy, and all the galaxies around us will be sucked into this thing , correct?

ALL the galaxies? No. (see above)
All the galaxies in our supercluster of galaxies? ... maybe... probably, even... given obscenely long time scales.

Well... either sucked into a black hole or ejected into inter-galactic space... perhaps to be captured by another galaxy, but the odds are against it. The amount of "empty space" out there is truly a rude amount to think about.

So how can the universe be expanding if there are black holes floating out there condensing entire galaxies into super dense masses?

Both of these processes are happening simultaneously. On "local" scales, gravitational sources win out and bind systems together. On the grandest length scales, though, the space between the isolated pockets of stuff is expanding, driving those pockets ever-further apart.

[BananaStand]

It is not. The galaxy is in orbit about Sagittarius A* (the SMBH in the Milky Way), much the same that the planets are in orbit about the sun.

All the galaxies in our supercluster of galaxies? ... maybe... probably, even... given obscenely long time scales.

Make up your mind dude. Is the milky way circling the drain or not.

[MadMojoMonkey]

Make up your mind dude. Is the milky way circling the drain or not.

Both. (see above)

[BananaStand]

Both. (see above)

No. Does not compute. Either the milky way is on its way into that black hole, or it isn't.

Assuming that it is, at some point, going to be consumed by the black hole, then wouldn't that make the black hole bigger, denser, and with a stronger gravitational pull? In other words, it will be able to consume things from further away. And so on, and so on.

So what's stopping these black holes from eventually consuming the entire universe?

[CoccoBill]

No. Does not compute. Either the milky way is on its way into that black hole, or it isn't.

Even though your car is probably heading to the junkyard some day, it isn't heading there now.

[BananaStand]

Even though your car is probably heading to the junkyard some day, it isn't heading there now.

Not an apt analogy. Not even close.

[MadMojoMonkey]

No. Does not compute. Either the milky way is on its way into that black hole, or it isn't.

Black holes don't "suck things up" any differently than any other massive body. I blame Hollywood for this one.

If something is in orbit, it will remain in orbit unless / until an outside influence affects that relation.
The pull exerted by gravity doesn't necessarily pull things into collision courses.

A galaxy isn't a rigid object. It's more like a gas, if we think of the stars as particles.

In order for something which is in orbit about the black hole to alter its course, it must change its energy.
Conservation of energy states that in order to change its energy, it must cause an equal and opposite change in energy to something else (the system around it).
If it is not interacting with anything nearby (the prevalent case for most stars not near the galactic nucleus), then it cannot change its energy, and the black hole can't "suck it in."
In order for something to be "sucked in" it has to deliver some of its energy to another body or bodies in the system.
So in order for something to be sent on a "sucked up" collision course, something else had to be sent the other direction.

So your question is incorrect. It assumes that ALL of the Milky Way will be consumed by the black hole or NONE of it. The actual answer is in between. Some of the Milky way will end up as Sagittarius A*, some of it will be flung into intergalactic space.

Assuming that it is, at some point, going to be consumed by the black hole, then wouldn't that make the black hole bigger, denser, and with a stronger gravitational pull? In other words, it will be able to consume things from further away. And so on, and so on.

As black holes consume matter, they grow in size and the gravitational effect on spacetime increases.

Yes, but this rate of expansion is slow, because most of space does not contain anything to consume... hence the name, I suppose.

So what's stopping these black holes from eventually consuming the entire universe?

Some of the stuff in the universe is moving away from the black holes at a rate faster than their escape velocity. The growing gravitational influence of the black holes is not fast enough to counter this.

When we look at the longest time scales and play the guessing game about what will happen, there is an extreme time scale at which all the stars have burned out, all the stellar remnants have burned out, and the only things left are black holes and a smattering of hydrogen atoms in the diffuse "vacuum" of space.

Eventually, even the black holes evaporate and the universe is left a diffuse gas of particles, each separated by their closest neighbor by distances too vast to overcome their relative velocities to ever stop them and pull them back into a bound state.

[BananaStand]

None of that sounds right.

Some of the stuff in the universe is moving away from the black holes .....

OR...they're moving toward other black holes that you don't know about.

I think it's pretty obvious that everything in the universe is getting pulled into black holes, and eventually they will start to converge, and coalesce until the entire universe is compressed into a singularity.

Then the big bang will happen again.

Just need to reconcile that with this whole "expanding universe" narrative. Maybe our observation point (earth) is being moved away from stuff so it just looks like the universe is expanding. I wonder if that has anything to do with the massive black hole sucking us in right now.

[Savy]

It's understandable to think your mum is at the centre of the universe.

[CoccoBill]

Not an apt analogy. Not even close.

Nah it was great, as car analogies always are.

[BananaStand]

It's understandable to think your mum is at the centre of the universe.

Honestly, if that's the best "your mum" joke you've got, especially when the topic of conversation is "black holes", then you should just go back to bed, and forget trying to be funny

[Savy]

Honestly, if that's the best "your mum" joke you've got, especially when the topic of conversation is "black holes", then you should just go back to bed, and forget trying to be funny

Once again if people are too stupid to get the joke I don't really care.

[MadMojoMonkey]

None of that sounds right.

Irrelevant.

QM sounds like loony talk. GR sounds like loony talk.
This is not relevant so long as these models produce accurate predictions of observable phenomena.

OR...they're moving toward other black holes that you don't know about.

Which either means
A) we already discussed that in the prior discussion and that object is NOT unbound, as it merely swapped its binding state from one SMBH to another.
or
B) the other black hole it's moving toward is receding away from it fast enough that they will never be bound to each other

I think it's pretty obvious that everything in the universe is getting pulled into black holes, and eventually they will start to converge, and coalesce until the entire universe is compressed into a singularity.

I'd love to see the evidence which makes this so obvious to you.
I can't wait to read your publication which clearly shows that decades of data have been misinterpreted.

Then the big bang will happen again.

Our current data suggests that the dark energy acceleration is prevalent over gravitational acceleration over the longest length scales.

Just need to reconcile that with this whole "expanding universe" narrative. Maybe our observation point (earth) is being moved away from stuff so it just looks like the universe is expanding. I wonder if that has anything to do with the massive black hole sucking us in right now.

The problem with your assertions is that there is a wealth of evidence which indicates that those hypotheses do not form or fit into a consistent model which makes accurate predictions about observable phenomena.

[BananaStand]

The problem with your assertions is that there is a wealth of evidence which indicates that those hypotheses do not form or fit into a consistent model which makes accurate predictions about observable phenomena.

So what you're saying is, I've made an unprecedented discovery.

If you don't watch your attitude, I might not mention you in my nobel prize acceptance speech.