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Author: Subject: Why does Fusion work?
chief
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Theres one interesting thing about the sun:
The total gravitational energy for disassembling the mass of the sun into infinity, i.e. the potential gravitational energy of it's mass
--> is said to be larger than the entire radiational energy which it emits during it's 10-15 billion estimated years of total lifetime ...

There are some MIT-physics-courses on youtube, and the Prof. calculated this in either this or one of the neighbouring videos:

======================

bbartlog
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Doesn't sound right to me...

Escape velocity for the sun = 6.3 x 10^5 m/s
Energy per kilo to remove is then ~ 2 x 10^11 Joules
Multiplying by the Sun's mass of 2x10^30 kg you then get 4 x 10^41 J to disassemble the sun
The actual figure is lower because you really want to integrate over the curve as removal gets easier (remember that the Sun's gravity grows less as you remove the mass piecewise)

Meanwhile the Sun emits 4 x 10^26 J/sec in energy, or about 1.25 * 10^34 J per year, so it would only take on the order of 10^7 or ten million years in order for the Sun to throw off enough energy to match the cost of its own disassembly.

I should probably actually look at the video. But there are two other factoids that make this idea seem implausible. One is that the radiation we see in the heavens is dominated by that generated by nuclear reactions. If the kind of gravitational or kinetic energy effects you describe were predominant we would expect more of the light we see to be generated by falling matter or the blackbody radiation from formation of new stars. Second, we already know that stars (even those much larger than Sol, with per-mass-unit energy costs for disassembly orders of magnitude larger) can blow themselves quite to pieces in a matter of hours from the energy of nuclear fusion.
IrC
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 Quote: Originally posted by 12AX7 Do you have proof that it is 7000 years old? Is that a testable hypothesis? Oddly, I can test that the universe is more than 0 seconds old, but how much older remains to be seen. I can at least tell with certainty that it is not -1 seconds old! Tim

I have to add something not discussed here. In fact in these type discussions the points in my mind are never looked at.

Olbers paradox for one. Why are we not all melting? Even at night. The best answer is the universe is too young still, it will be hotter later when all that light reaches us. So we see a dark night sky. If from this fact we assume the universe is not infinite in age (and likely not static) but we can make measurements of what light there is and do many calculations which if correct should all come together and they do resulting in we have a good handle on factoids about the universe. From this and knowing by other means details of the universe like : ~14 billion years of age, approximate size, number of stars and average density and knowing other factors such as the total combined light from various sources we get a clear picture of the facts. In essence we may not know everything but these facts we are clear on, leave no room for consideration of ideas to quote Gump "as stupid as stupid gets".

Consideration of the brightness of the night sky includes red shifting from expansion, dust, apparent brightness of stars (remember the squares cancel meaning distant stars are very bright for the distance) and adding the afterglow, and so on. We can assume the expansion will always keep the night sky dark since as the light finally reaches us and adds together so much red shifting has occurred. Good then that as time goes by we can still use our telescopes at night.

The point I am making is this means the universe could be much older than we think yet from many measured parameters we can be sure it is not younger than around a billion years plus the age of the oldest globular cluster. Amazingly enough we arrive at ~ 14 billion years.

Another point: take the number of stars, surface brightness, angular area, and so on. Consider all stars as old as the sun. If the universe was 7000 years old and had no real expansion time all the light from all stars we see has had time to get here with little red shift loss. The light would vaporize titanium on the surface of the earth. Even at night. If we assume magically it is 7000 years old and the light just started from the known distances the sky would be very much darker and this also we can measure. Not to mention having to say the universe is younger than the things in it. To get the oil we burn and the fossils we see it takes little effort to show therefore the universe is also much younger that the earth if you can buy that one.

Without all the details as to why I might add if we are close on the Hubble constant then we know the maximum is around 20 billion years so again I believe we all have a good handle on the age.

From another view. Clearly the universe must be at least as old as the oldest object in it. We have such good data on the most distant globular clusters we know they are around 12 or 13 billion years old. This provides good evidence we are correct in our 14 billion year estimate. Now add this. We know enough about stars to know a lifetime is maybe 10 billion years maximum. Where did the matter we are made of come from. From supernovas. So at least one and a half stellar cycles must have occurred for us to be made of elements other than H and He and be living under a second generation (minimum) star already halfway through its life. Likely at least two supernovas are needed to account for all of the heavier elements in just our solar system. I believe all the facts we now know with great certainty gives us a good idea the universe is at least 10 billion years plus the suns age old at the very minimum.

[Edited on 2-24-2010 by IrC]

"Science is the belief in the ignorance of the experts" Richard Feynman
tom haggen
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fdsa

fdsaf

[Edited on 27-2-2010 by tom haggen]

[Edited on 28-2-2010 by Ramiel]

N/A
IrC
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I was hoping someone would be interested in discussing my points on Olbers Paradox, yet all I see is Tom the jerkweed using the site for free image hosting. No actual post just some cryptic letters and really do we need to see the damn spark plugs. Here is an idea Tomweed, start your own thread titled "my image hosting ripoff". Better yet pay for your own hosting instead of ripping off the people who are paying for this site.

Or irritating the people like me who could give a rats ass about your spark plugs in a picture annoyingly large.

"Science is the belief in the ignorance of the experts" Richard Feynman
hissingnoise
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I'm not irritated; I'm amused and perplexed - I like a bit of surrealism!
The reason it's here is kind of incidental?
But Olber's Paradox seems to point to The Big Bang and this reduces us and our universe to mere schrapnel.

[Edited on 28-2-2010 by hissingnoise]
hissingnoise
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Wow! Perfection just got better?

(Oops! Not Whimsy!)

[Edited on 28-2-2010 by hissingnoise]
IrC
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 Quote: Originally posted by hissingnoise I'm not irritated; I'm amused and perplexed - I like a bit of surrealism!

You may be right.

As to shrapnel I can live with this so long as the universe outlives me. Never liked the cycling crunch thing, I hate small spaces.

[Edited on 2-28-2010 by IrC]

"Science is the belief in the ignorance of the experts" Richard Feynman
hissingnoise
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I'd prefer the steady state myself; I find all change unsettling. . .
IrC
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 Quote: Originally posted by hissingnoise I'd prefer the steady state myself; I find all change unsettling. . .

I guess with nothing new or useful added by now no one is going to discuss Olbers on proving the age so I'll move on to more interesting things (or threads). Would not have bothered to make this post except I wanted to comment on your S.S. preference. That is, if it were static we would be flash frying now or soon since the red shift from expansion would not exist. So give me shrapnel for creation and moderate weather. After 25 years in the Arizona desert I have no further need for excess heat.

[Edited on 3-2-2010 by IrC]

"Science is the belief in the ignorance of the experts" Richard Feynman
Rosco Bodine
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My theory is that everything we see and think we know and everything we experience is sort of like that movie the Matrix .....a contrived illusion which
operates according to what we estimate are the "laws of nature" .....but we only know a fractional part of all that is .....and by design or inherent limitiation of the form of being which we are....a fraction of the knowing it all is our operational ceiling.
IrC
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I think the string and brane theories are getting close to what is real and dimensions likely do number up to 11 or so. From this and knowing we cannot perceive even a half dozen of these dimensions creation could be very different in whole than what we know. Yet you can carry this too far. If for example our belief of the universe consisted of only what is in our visual range in the sky above we might conclude it is all nothing more than an illusion created by some deity and has no solid reality. Later when a meteor comes through the roof and levels the house would we alter the belief system. Of course if none of it was really real we would wonder where the heat of the sun is coming from.

Or a 1930's physicist sees a positron and an electron (yes lets assume he can see it for now) coming from the collision of two photons of more than .511 Mev energy. He concludes there are two particles. A 21st century physicist looks at this and concludes there is only one particle the bulk of which exists in dimensions outside of our perception today and the particles seen in the 30's are merely extensions in our "lower" dimensions of this single entity and decides this is the source of quantum connectivity between the opposite particles. Who is right one wonders.

Better yet is anyone going to bring the cause of fusion back up or has the thread forever disintegrated into philosophy.

"Science is the belief in the ignorance of the experts" Richard Feynman
Rosco Bodine
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Philosophy is but a shadow of the dimensions of the religion it once was,
and fusion is but entropy in retreat toward singularity, fleeing from an
"expanding universe" where its place was no longer found ....
but relatively speaking, while "travelling" towards its destination it goes
"away" from its previous "remainder universe"
still apparently expanding ......looking in the rear view mirror at a view which just became every other direction than straight ahead! What dimension is this
"straight ahead" when you can never go "back home" anymore ?
IrC
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You win, you have me too confused to reply.

Edit to add: oddly there seems to be some logic in this.

[Edited on 3-2-2010 by IrC]

"Science is the belief in the ignorance of the experts" Richard Feynman
Rosco Bodine
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I can't answer my own question really ....but visualizing it , it has a shape and it is spherical.
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 Sciencemadness Discussion Board » Fundamentals » Miscellaneous » Why does Fusion work? Select A Forum Fundamentals   » Chemistry in General   » Organic Chemistry   » Beginnings   » Responsible Practices   » Miscellaneous Engineering and Equipment   » Reagents and Apparatus Acquisition   » Electronics   » Process Engineering   » Materials and Metallurgy Special Topics   » Analytical Chemistry   » Electrochemistry   » Energetic Materials   » Biochemistry   » Radiochemistry   » Computational Models and Techniques Literature and Documentation   » Sciencemadness Wiki   » Prepublication Non-science   » Forum Matters   » Legal and Societal Issues