The Astrophysical Hotseat

[extropalopakettle]

Stretchy stuff is composed of molecules that have bonds between them and interact with one another. How does it happen with space?

[firemeboy]

Quantum Mechanics gives us the answer. And the answer is Silly Putty.

[Samadhi]

Originally posted by Vinny:

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Some one ought to move this thread to Educator Idea. We keep losing it to the obscurity of page 2 in OT.

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Originally posted by Borodog - thread owner:

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Sure

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Okay.

[Samadhi]

If anyone thinks this doesn't belong here I'll punt it back.

[pikachamp]

the same way, but instead of stretchy stuff, we have the SPACE-TIME CONTINUUM

[extropalopakettle]

Well no, not the same way at all, because the way that "stretchy stuff" is deformed at places other than the exact point where you press your finger against it is through interaction of the molecules the "stretchy stuff" is made of. We could be more detailed, but that's what's at the heart of the explanation. So, what's at the heart of the explanation as to how space get's deformed? It isn't interaction of molecules. And I don't mean equations that describe the deformation (you could come up with these for stretchy stuff too), but an explanation of the mechanism that makes it happen. That is, if I describe with equations how stretchy stuff deforms, I can explain the mechanisms that cause it to deform just that way. If I describe with equations how space itself deforms, can I explain the mechanisms that cause it to deform that way?

[pikachamp]

*murders extro*
now go ask einstein

[extropalopakettle]

I think maybe the point is that at some point, answers to questions like Mikko's "How does gravity reach a body?" can be no better than "It just does" (when "how" is meant in the sense of what "what makes it happen", as opposed to "what is it like when it happens"). It may not be the case with this question in particular, but it's probably close.

[VinnyQ]

Borodog, a rambling proffesor of mine once rant at me for the consiparacy that is our current Energy Source Situation. He said that we can very well be harnishing energy from water, which is abundent and produces carbon dioxide and hydrogen as waste, instead of using polluted oil & coal. The reason we haven't, according to him, was because all the big shots, OPEC & our government and other countries high circles, want to monopolize the oil industry and keep making money from it.

Is there any truth to this?

[VinnyQ]

also, how does one go about building a telescope?

[extropalopakettle]

And, how does one become a professor, when one's only skill is incoherent babbling?

The problem with using water as fuel would probably be all that hydrogen waste produced.

[CrystyB]

Umm, remember the baloons? Anything that is lighter than air has a tendency to move away from the Earth. H₂ more than anything else. To find out the more probable reason, apply a simple elimination technique... In fact, CO₂ increases the greenhouse effect, doesn't it? And i guess it'd be more out of water (which is 88% oxygen to go into CO2) than out of burning oil products...

if we would find a way to ionize water cheaply, would there be any reason to pick oxygen to use for fuel? Couldn't both H₂ and O₂ ions be used?

[extropalopakettle]

OK, I was joking. How can you get CO₂ from H₂O? And the hydrogen (in combination with oxygen) is the cleanest burning fuel you'll ever get (Bush was just babbling about it minutes ago during his state of the union address - he's going to personally fund the development of hydrogen powered cars, or something). The hydrogen will be generated by electrolysis of water, using electricity produced by generators, powered by engines running on free oil from Iraq (well, I'm listening to the speech now - he hasn't got that far yet).

[MacadamiamaN]

It's not like the hydrogen powered cars back in the day-- where the slightest bump would make them explode, these "hydrogen" cars are more commonly referred to as "fuel-cell" cars.

The fuel cell is the most innovative and rewarding invention we will have in the years to come. The early 1900's were known as the years when electricity was developed. 100 years from now, we'll be looking at right around now as the time that the fuel cell was developed. In the simplest sense, the only pollution from a fuel cell is water - that you can pipe to a cup in the cup holder while you're driving, in theory

Am I wrong in stating that Ford was already given a $100 million government grant for the study of fuel cells? I think I read this somewhere. And they also came out with a prototype.

Fuel Cells (in a far-simpler form) are also available for cell phones and stuff, just look on ebay...

[VinnyQ]

Ok, I did get that backward. It is as the nut and other'd said, harvest hydrogen and get water as a by-product. I just quoted the proffesor wrong, not his fault.

He was practically foaming at the mouth spraying me with spits telling me this though, how we can be using this as an alternative energy source right now, as oppose to oil, but it is not happening b/c of "them".



[This message has been edited by VinnyQ (edited 01-29-2003 12:16 AM).]

[ML]

Extro's right (post 172):

To restate, for those too lazy to read all the posts.
Once you have the Hydrogen it is the absolute cleanest source of energy. You can consume all of the byproducts (which is just water).

But currently, the only way to get the hydrogen is by burning oil/coal. Well, not quite true, but it is the only way we have to getting the quantities that we need. What's more, the barrels of oil needed to power a car for 1 mile would probably be higher, due to ineffeciencies of converting oil->electricity->hydrogen->electricity->motion (rather than gasoline->motion like we do now)

That being said, it would still do good things. Allow for a greater range of energy sources, concentrate polluting activities in plants which maybe able to control it better than cars, get people thinking about other options, fewer moving parts in cars means more reliable cars.... But it is not a solution.

*steps off soapbox*

[This message has been edited by ML (edited 01-29-2003 09:27 AM).]

[One Skunk Todd]

Or maybe we could just use electicity generated by nuclear reactors to split the water and take oil out of the equation altogether.

[This message has been edited by One Skunk Todd (edited 01-29-2003 04:48 PM).]

[CrystyB]

for a totally offtrack person like me where does the NR gets his energy to do funny stuff to all those nuclei? i think i just remembered - Radioactive emissions from Uranium/Polonium/the-likes? And i think all the byproducts of NR are quite hard to dispense of, IRC...

[extropalopakettle]

[VinnyQ]

So the world is save then, right!??! What are we waiting for? Why aren't we on this like flies on doo doo?

[Beartalon]

Oil company profit?
Government taxes on gasoline?
Research that upsets the status quo is not always well received.

Otherwise, Canada would have had a first-rate air force of Avro Arrows...

[This message has been edited by Beartalon (edited 01-30-2003 01:00 PM).]

[extropalopakettle]

Don't forget the hysterical reaction of environmentalists to all things nuclear.

[CrystyB]

"stable geologic structures"? Where exactly could those be found?

And hysterical reactions were at first meant to anything radioactive enough, the drift was due to fear of unknown, right? But after all, there is a bit of reason into all that...

[Vinny]

~drags thread up by the nose

[Chuck]

First Planet Found by Microlensing

[Samadhi]

Tonight I watched a show about galaxies. I learned that it is relatively accepted that each galactic black hole's size is directly related to the size of it's 'host' galaxy. Later they stated that it was surprising that the speed of the outer most stars were directly correlated to the size of the black hole. This somewhat baffled me and was not explained. Shouldn't the speed of the outer stars be directly related to the size of the galaxy and therefore the size of the black hole? Why would that be surprising?
_________________
And he lived happily ever after. Except for the dieing at the end and the heartbreak in between.

[kevinatilusa]

I'm not so sure about the speed of the outer stars being proportional to size.

If we let M be the mass of a galaxy, R the radius of the galaxy, it seems like we should have:

Angular momentum=constant*M (each kilogram of mass contributes whatever angular momentum it had to the system when it gets sucked in, and that should be approximately uniform on average).

But we also have Angular Momentum=(moment of Intertia)*(angular velocity)=constant*MR^2*(angular velocity).

Solving, angular velocity is constant*1/R^2, so the velocity of the outer stars should be about R*(angular velocity)=constant*1/R . Therefore the velocities should actually decrease with mass.

I'm not sure if this is right, particularly the assumption angular momentum is proportional to mass, which assumes that the particles all tend to be rotating in the same direction when they arrive. If that assumption is wrong, another possibility is Ang Mom proportional to M^(0.5) (which would be assuming the momenta are approximately randomly distributed).

In other words, I could well be pulling this out of my behind.

[Dr. Borodog]

It is actually quite surprising that the rotation curves of galaxies do not fall off with distance from the center. It is a clear indication of "dark matter," and was in fact the original reason it was proposed.

A star is bound to it's galaxy by gravity:

F _G =GM(r)m _* /r ² ,

where m _* is the mass of the star, and M(r) is the mass of the galaxy contained within that star's orbit, clearly a function of r. We presume the star orbits in a circle, so:

F _G = m _* v(r) ² /r,

where v is the star's orbital velocity, also presumably a function of radius.

Solving for M(r) we find:

M(r) = rv(r)/G.

If all the mass were at the galactic center, M(r) would be constant, and v would be inversely proportional to r. This is a pretty good approximation outside the core, where the mass of the outer stars are pretty negligable to the mass of the core. So we would expect the velocity curve of galaxies to drop off inversely with radius out side the core.

But it doesn't. It is flat. This tells us that the mass of the galaxy increases linearly with radius. We can't see this mass. Since mass is proportional to density times volume, and volume is proportional to r ³ , it appears there is some "dark matter" surrounding galaxies, with a density that falls off with increasing radius, like a cloud centered on the galaxy.

[impossibleroot]

This just occured to me -- could the 'missing mass' simply be hiding in the geometry of the Universe, in the 4th spatial dimension that space is curved into and that we can't perceive (because our brains can only pick up on 3 dimensions)? Or am I taking the Flatland analogy a little too seriously?

BTW, I'm glad I found this thread -- I did my BS in Astrophys, but decided to get immediately into teaching (high school) instead of pursuing a research career and higher degrees. Congrats on the successful defense of your thesis, Dr. B!

[Chuck]

Universe Measured: We're 156 Billion Light-years Wide!

[Digit Ne]

Just popping in to say I enjoyed reading through this thread when it was bumped up - I've enjoyed reading about astrophysics from other sources, and though the math scares me badly, this thread has been worthwhile.

Congratulations also to Dr. Borodog...

[Chuck]

[Hitchhiker]

A shameless plug for a truly fabulous podcast:

http://www.slackerastronomy.org/

[austinap]

I have a question. If the universe one day shrinks back in on itself as many theorize is possible, wouldn't this violate the laws of thermodynamics (that entropy is always increasing)? It seems to me the only way the big bang can coexist with thermodynamics is if the universe continues to expand indefinately, what am I missing?

[Samadhi]

Compacting does not increase order or decrease entropy.

Apart from that, prevailing opinion is that not only is the universe expanding, but that the rate at which it's expanding is excellerating.

[austinap]

How not? One theory I've heard before is the 'never ending cycle of expansions on contractions.' That is, the big bang happens, the universe expands, and then it eventually collapses in on itself and it all happens over again. Wouldn't entropy have to decrease for this to happen?

[Samadhi]

Which is one reason it's not a very sound theory.

[austinap]

just curious, it didn't make any sense at all to me but then again I don't study astrophysics with much intensity.

[Coyote]

Entropy Production and Thermodynamic Arrow of Time in a Recollapsing Universe

I hope that clears things up for you.

[Samadhi]

uh....no comment