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AuthorTopic: The Universe
Electric Sheep One
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Dammit, Jim, I'm a physicist, not an oncologist.

I believe, though, that the crucial feature of a tumor is that it manages to fill itself with blood vessels that connect to the rest of the network, so that its interior cells get supplied with oxygen. Without that nasty capability, a mere mass of cells could not keep on growing, because the inner ones would starve and die.

So since the universe does not seem to have any blood vessels, or anything like them, I'd say the tumor model is a bit off.

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quote:
Originally written by Student of Trinity:

Dammit, Jim, I'm a physicist, not an oncologist.

I believe, though, that the crucial feature of a tumor is that it manages to fill itself with blood vessels that connect to the rest of the network, so that its interior cells get supplied with oxygen. Without that nasty capability, a mere mass of cells could not keep on growing, because the inner ones would starve and die.

So since the universe does not seem to have any blood vessels, or anything like them, I'd say the tumor model is a bit off.

Since this has turned into the topic where we all show off our scientific knowledge, I may as well say that there are actually 6 features that nearly all types of malignant tumour must have:

* Sustained angiogenesis (blood vessel formation) -- the one you mentioned. Each cell has to be within a certain distance of capillaries in order to receive enough nutrients to keep growing. Cells more than a millimetre or so from the nearest capillary bed don't grow very well.

* Growth signal self-sufficiency. All animal cells ordinarily need external signals in order to survive and grow (mostly in the form of proteins or other hormones, either circulating in the blood or secreted by nearby cells). Normally, the cells of tissue from an adult organism receive only enough growth factors to keep the tissue in a steady state, and the signal will be turned down further if excessive growth of that tissue type occurs. Certain mutations allow a cell to proliferate even in the absence of growth factors.

* Resistance to growth-limiting signals. This is pretty much the same deal as above (signals that limit growth are produced, and more are produced when the tissue overgrows), but the actual molecules involved are different so two separate genetic mutations are normally required to confer both, which is why this gets its own category.

* Ability to proliferate indefinitely. Certain internal processes such as telomere shortening set inherent limits on the number of times most cells can divide before they become "senescent", stop dividing and eventually die. However, some genetic mutations allow these limits to be bypassed. If this explanation sounds like a bit of a handwave, that's because it is; the processes underlying cell senescence are relatively poorly understood.

* Resistance to cell death signals. Normally, damaged DNA and abnormal protein expression can be detected by various mechanisms involving both the cell itself and other cells, and signalling pathways are activated that cause the cell to die.

* Ability to invade and spread through tissue. This often involves the production of enzymes that break down the extracellular proteins that normally hold cells in place.

Of course, in non-solid tumours such as the leukaemias and lymphomas, a couple of these factors aren't applicable.

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damn you, i am still in high school
but i am sharp, both in inteligence and curiosity

probably more on curiosity

say, if i wanted to make an anti-matter engine, capable of producing massive amounts of energy, how should i proceed?
Posts: 38 | Registered: Sunday, April 3 2005 08:00
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quote:
say, if i wanted to make an anti-matter engine, capable of producing massive amounts of energy, how should i proceed?
1) Get a whole bunch of antimatter from somewhere. (Non-trivial problem: antimatter doesn't occur in significant amounts in nature, so you'll need to produce it. This requires big fancy particle accelerators and the input of much more energy than you'll get out.)

2) Collide it with some matter. (Non-trivial problems: storing it safely until you need it, probably using magnetic containment, and avoiding blowing yourself up when you do use it.)

3) Collect the energy from the resulting annihilation. (Non-trivial problem: how the hell do you convert gamma rays into useful energy? I suppose you could absorb them with a lead block or something and run a heat engine off that, but that's pretty wasteful.)

Conclusion: antimatter is for energy storage, not energy production. And that's only if you have a way to produce it, safely store it and extract the energy.

Here's a somewhat curlier question, addressed to better physicists than I: assuming Hawking radiation is a real phenomenon, how feasible would it be to use a microscopic black hole as a matter/energy conversion device?

Creating the hole is obviously the first difficulty; Hawking says a really big hydrogen bomb might work, but I'd prefer a plan that works on a somewhat smaller scale than extracting the deuterium from all the world's oceans. I'm thinking that firing a whole bunch of lasers or linacs from different angles on a small piece of matter might work.

Preventing the hole from eating Earth is another problem; I'm thinking it'd be best to create the thing in a low Earth orbit, or possibly even a solar orbit. Extracting the energy in a useful form is the third problem. Any advice on any of the steps necessary in the process would be welcome.

[ Saturday, April 09, 2005 16:27: Message edited by: Levitating Netherlander ]

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thanks a lot. i would like to see you stating something similar about nuclear energy 100 years ago.

don't be so negative.
and i already knew the stuff you said

i assume that if we react matter with anti-matter in magnetic containment, we should obtain gamma rays.
isn't there anyway to turn highly energetic radiation in to useful energy?

[ Saturday, April 09, 2005 16:30: Message edited by: imho ]
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Warrior
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Radioactive materials, like Uranium produce gamma rays, too (as well as alpha particles) that's why they're so bad to be around. Nuclear power plants work by using radioactive Uranium to heat up water, and generated energy that way (http://people.howstuffworks.com/nuclear-power.htm). You could do the same kind of thing with antimatter. Though, you don't just get gamma rays from antimatter, though, gamma rays can decay into other particles (eg, http://particleadventure.org/particleadventure/frameless/eedd.html, where an electron and positron annihilate to produce a photon which decays into D mesons :) )

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Posts: 103 | Registered: Sunday, June 20 2004 07:00
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quote:
Originally written by Levitating Netherlander:

[QUOTE]Preventing the hole from eating Earth is another problem; I'm thinking it'd be best to create the thing in a low Earth orbit, or possibly even a solar orbit. Extracting the energy in a useful form is the third problem. Any advice on any of the steps necessary in the process would be welcome.
If you would reduce all mass of the earth to a black hole, it would absorb all matter within a range of a few millimeters. Thus, the microscopic black hole wouldn't be very dangerous, but surely hard, if not impossible, to control.

[ Sunday, April 10, 2005 10:35: Message edited by: Mind ]
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quote:
If you would reduce all mass of the earth to a black hole, it would absorb all matter within a range of a few millimeters. Thus, the microscopic black hole wouldn't be very dangerous, but surely hard, if not impossible, to control.
A microscopic black hole would be dangerous despite its small size, because even if the actual event horizon is tiny, the gravity well around it would draw in surrounding matter at a great rate. A collision with Earth's surface would therefore be disastrous.

[ Sunday, April 10, 2005 12:53: Message edited by: Thuryl ]

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Another problem with small black holes is the Hawking Radiation which causes a black hole to lose its energy. This is proportional to the surface to volume ratio of the black hole, so a small black hole fades away faster than a big one.

As far as antimatter, the problem with it as a conventional electricity source is there is no way period to get net energy out. Space propulsion might have some hope. This pesky first law of thermodynamics prevents us from producing copious amounts of antimatter. In other words, because of the second law, we must spend more energy to make it than we could ever get back.

The reason nuclear fission works for power plants and warships so well is that there is plenty of 235U lying around. A majority of the energy is deposited by fission products as well, helping it. Nuclear fusion has the fact that there is tons of deuterium in the form of D2O in the worlds oceans making it viable. The energy conversion comes from the heating by neutron interactions with the walls or direct conversion into electricity from charged particle products from advanced fuels. Antimatter does not have that luxury.

On antimatter power cycles: one would never use positron to gamma decay for energy source. Antiproton-proton pairs become high energy pions upon annihilation . These are what would be harvested, not the gamma rays.

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anti-protons also have the advantage that they could be (relatively) easily contained by a negative electrostactic feild.

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Electric Sheep One
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Thanks, Thuryl, for the info on tumors.

Making a Hawking furnace would really be a lot like starting a fire -- perhaps it is a problem for the boy scouts of advanced species. You'd need to apply enough force to compress stuff within its Schwarzschild radius, which probably means overcoming neutron degeneracy pressure, if you use ordinary matter. But once the horizon formed, I guess you could just keep shoveling stuff into it, to keep it from shrinking as it radiated.

One really good thing to shovel into it would be a high net electric charge, so that you could manipulate the thing with electromagnetic fields. Hold it from falling through the floor with a nice E-field, though, and you could sit back and toast your tootsies.

Well, kind of. The temperature of a Hawking radiator is inversely proportional to its Schwarzchild radius, so a tiny black hole would be really hot. Depending on how tiny you made it, you might be dealing with gamma rays here too, in which case you might want to keep your shoes on.

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Thanks for the answer. A lot of what you say I'd assumed would be the case; as you say, setting up a moderately stable black hole is the tricky part, and after that it's just a matter of keeping it fed.

quote:
Originally written by Student of Trinity:

One really good thing to shovel into it would be a high net electric charge, so that you could manipulate the thing with electromagnetic fields. Hold it from falling through the floor with a nice E-field, though, and you could sit back and toast your tootsies.
How well would this work in practice? Intuitively, it seems to me that a black hole with a particular charge would be more likely to emit particles of its own charge than of the opposite charge, and therefore you'd have to feed it a constant stream of charged particles to keep it charged. Admittedly you'd only need to give it a relatively small electric charge in order to manipulate it in useful ways, but it still introduces inefficiencies.

quote:
Well, kind of. The temperature of a Hawking radiator is inversely proportional to its Schwarzchild radius, so a tiny black hole would be really hot. Depending on how tiny you made it, you might be dealing with gamma rays here too, in which case you might want to keep your shoes on.
Does a radiating black hole actually behave as a black body? The explanation of Hawking radiation in A Brief History of Time seems to imply that the energy of the particles emitted by a black hole isn't dependent on the hole's size, only the rate of emission is (and the rate is dependent on the hole's surface-area-to-volume ratio).

EDIT: Wikipedia says a black hole does indeed behave as a black body. Admittedly it's not a scientific source but I'm inclined to trust it.

Hmm. It also brings a bit of bad news; to make a black hole that lasts even one second, you need to start with over 200 metric tons of matter. That's an awful lot of mass to put in the same place at the same time. Maybe if we collided a few asteroids together at relativistic speeds we might be able to get something going, but that might not be any easier than Hawking's hydrogen-bomb idea.

[ Sunday, April 10, 2005 20:54: Message edited by: Thuryl ]

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Now, do we actually know that there's more antimatter than matter in the entire universe, or do we just know that about this surrounding area?

If the latter, then there would be a possibility of finding a large source of antimatter elsewhere -- like, galaxies away, but still in existence. So in several thousand (or million/billion) years, our energy problems would go away.

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quote:
Originally written by imho:

thanks a lot. i would like to see you stating something similar about nuclear energy 100 years ago.

don't be so negative.
and i already knew the stuff you said

i assume that if we react matter with anti-matter in magnetic containment, we should obtain gamma rays.
isn't there anyway to turn highly energetic radiation in to useful energy?

CERN's public statement concerning "Angels & Demons" by Dan Brown

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We know there's no (significant) antimatter in the universe. There're various ways we know this, the most obvious being that we don't see huge bursts of radiation caused by clumps of matter interacting with clumps of anti-matter. There are also other ways, such as the isotropy of the cosmic background radiation, that indicate there is no anti-matter, too. There are other things that tell us this, too. Any anti-matter found in the universe would be created by recent (that is to say, not from the big bang) processes, like radioactive decay, and won't be found in large (as in, bigger than small collections of molecules) quantities.

[ Sunday, April 10, 2005 21:15: Message edited by: cfgauss ]

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Here is the scoop on power that seems too good to be true: it is. While it would certainly be spectacular (if more or less pointless) to create a black hole artificially, there would be no way to exploit it to create more power than had been invested into the black hole itself.

The reason setting things on fire or fusing them works is that the energy trapped up in atomic, molecular, etc. bonds is, so far as we are concerned, 'free'; it was caused by natural forces outside of our control. This is as opposed to stuff like antimatter and black holes, which could be created by CERN or something like it - but CERN has to get juice from somewhere...

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quote:
Originally written by Bad-Ass Mother Custer:

Here is the scoop on power that seems too good to be true: it is. While it would certainly be spectacular (if more or less pointless) to create a black hole artificially, there would be no way to exploit it to create more power than had been invested into the black hole itself.
So you chuck inert matter into it. The energy you get out of it comes from the mass-energy of the matter you put in. Sure, eventually you run out of matter that isn't useful for any other purpose, but at the moment there's no shortage of matter in the universe.

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quote:
A microscopic black hole would be dangerous despite its small size, because even if the actual event horizon is tiny, the gravity well around it would draw in surrounding matter at a great rate. A collision with Earth's surface would therefore be disastrous.
What is the difference between the event horizon and the gravity well? What does "gravity well" mean?

quote:
EDIT: Wikipedia says a black hole does indeed behave as a black body. Admittedly it's not a scientific source but I'm inclined to trust it.
A black hole behaves as a black body because not even light can escape it, despite its absolute speed.

quote:
Now, do we actually know that there's more antimatter than matter in the entire universe, or do we just know that about this surrounding area?
I've read that, in the singularity, there was only an extremely slight asymmetry between anti-matter and matter; There was 10^-10 more matter than anti-matter.

However, if anti-matter was dominating the universe, of course, what we call "anti-matter" now would be called "matter" and vice versa.

[ Monday, April 11, 2005 02:01: Message edited by: Mind ]
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quote:
What is the difference between the event horizon and the gravity well? What does "gravity well" mean?
An event horizon is a discontinuity in the observable universe; nothing on the other side of an event horizon from us can be observed, because no information can get from there to here.

A gravity well is simply the term for the distortion in spacetime caused by a gravitational field. Any object with mass has one. Things will still accelerate toward a black hole because of its gravity, even if they're outside its event horizon. (I must admit, though, I haven't actually done the number-crunching on what sort of conditions are required to make the gravitational pull of a microscopic black hole stronger than the electromagnetic forces holding matter together. Since a microscopic black hole can actually be much smaller than a single atom, this is a significant issue when trying to feed it.)

quote:
A black hole behaves as a black body because not even light can escape it, despite its absolute speed.
It's true that a black hole fits the usual definition of a black body (a completely non-reflective object), but since the way it radiates energy isn't quite normal, I thought it might not behave as a normal black body. Apparently it does, though.

[ Monday, April 11, 2005 03:02: Message edited by: Thuryl ]

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Electric Sheep One
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Thuryl's right, Custer. Creating the black hole and letting it decay wouldn't win you anything, but keeping it fed would let you convert matter God left lying around into heat. It would be just like combustion or fusion, only a heck of a lot harder to get going, but also a heck of a lot more efficient once fired up.

It is far from obvious that black holes should really behave as radiative black bodies. Hawking himself was quite surprised by this result, and it appears to be something of a mathematical fluke (though everyone hopes that it's really a profound and necessary truth that we don't yet fully grasp).

I'm not actually sure whether a charged black hole radiates charged particles preferentially. A similar question is whether a spinning black hole tends to radiate angular momentum; I'm also unsure about this. These are the kinds of calculation that somebody ought to have done by now, and may well have. It has been about ten years since I was really actively following black hole physics, but I don't remember any papers about these issues though. Good questions.

For what it's worth, I'd bet the answer is, no. But if the answer is Yes, you'd just have to keep feeding charge to the black hole as well as energy. Tending and feeding a Hawking furnace might well be as fussy a business as keeping a campfire going in a storm. Could be well worth it, though.

About antimatter in the universe: I have taught this stuff, about how we think there is hardly any antimatter anywhere, but I have to admit I don't quite understand myself why we are so sure that distant parts of the universe are not dominated by antimatter. Matter is thought to have (very slightly) outweighed antimatter in the early universe, through a statistical fluke. But it is common in such cases to have a domain structure, in which the chips fall differently in different places.

We know virtually nothing about the intergalactic medium; if there were genuine chasms of vacuum between matter and antimatter regions, there might be very little in the way of annihilation radiation for us to detect. And I'd be surprised if our spectroscopic resolution was good enough to rule out lineshifts, in very distant galaxies, due to CP violation. I guess I know people I could ask about this, but I never have.

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quote:
A gravity well is simply the term for the distortion in spacetime caused by a gravitational field. Any object with mass has one. Things will still accelerate toward a black hole because of its gravity, even if they're outside its event horizon.
Yes. Gravity reaches to the far ends of the universe. Apologize my forgetfulness.

However, the influence of the gravity of the supposed microscopic black hole would be very insignificant out of range of a few micrometers, isn't it?
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I'd imagine it would be very difficult to make your black hole at a nice size, since as soon as you get your 200 tons of matter together, you're going to have more energy spraying back at you than you'd get if you detonated all the world's nuclear weapons at once. So really, you'd need vastly more matter than that to get started, and some way of collapsing it uniformly.

Oh, and when you forget to feed it, it'll really bite you.

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Electric Sheep One
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Yeah, it's unstable against catastrophic shrinking. Shouldn't be too big a problem if you just get it big enough: in principle you can do feedback control on the temperature. The Hawking furnace has the odd property that you cool it down by feeding it faster. It's getting it big enough to be in a safe operating range that must be tough.

Also, it might be a pain putting this kind of heat engine into a vehicle, because it has to be pretty darn massive. You might use it to generate the power needed to produce antimatter, then run your starships on matter-antimatter batteries.

Now I'm really wondering whether anyone has published a paper on the engineering issues in making and operating a Hawking furnace. I believe I just invented that name for this device, but it's an obvious enough concept that I'd be surprised if no-one had written it up. On the other hand I'd also be somewhat surprised if they had and I hadn't heard of it, and I haven't. If it hasn't been written yet, it could be a quick and easy publication ... [would grin hungrily, except that every other idea he has ever had for a 'quick and easy' publication has turned out to be very far from either, sigh].

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great stuff in here

just a question?
most of us aren't graduated in physics, or some aren't even graduated.
is all this debate the result of our curiosity?

btw, Earth has a magnetic field right? is there anyway we can use it to produce energy, or is it to weak?

[ Monday, April 11, 2005 11:40: Message edited by: imho ]
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quote:
Originally written by Student of Trinity:

Also, it might be a pain putting this kind of heat engine into a vehicle, because it has to be pretty darn massive. You might use it to generate the power needed to produce antimatter, then run your starships on matter-antimatter batteries.
You could tell I was looking for this information for an SF story, huh? :P

But yeah, I was definitely thinking of it as a power plant rather than an engine. (Transporting a Hawking furnace through interstellar space would be a huge effort anyway, since you need to take all its food with you.)

quote:
Now I'm really wondering whether anyone has published a paper on the engineering issues in making and operating a Hawking furnace. I believe I just invented that name for this device, but it's an obvious enough concept that I'd be surprised if no-one had written it up.
Seems as if you did indeed invent the term, since Google gives no results for it. I did a search cross-referencing "energy extraction" and "black hole", but all the links I can find seem to talk about extracting energy from its rotation, not from the Hawking radiation.

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