Comment by dogma1138 | Hacker News Reader

Comment by dogma1138 | Hacker News Reader

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Again gravity is what maintains the reaction going, without it the gas would expand and the reaction would stop.

I understand how fusion works, what you neglect is that gravity is what allows you to counter the nuclear forces to cause protons to fuse in the first place, and what keeps the entire thing from blowing out.

Hence stars are in constant balance between gravitational collapse and their outward pressure caused by fusion.

“An interstellar cloud of gas will remain in hydrostatic equilibrium as long as the kinetic energy of the gas pressure is in balance with the potential energy of the internal gravitational force. Mathematically this is expressed using the virial theorem, which states that, to maintain equilibrium, the gravitational potential energy must equal twice the internal thermal energy.”

On earth we exchange gravitational potential with electromagnetism but we still need to apply the same force to counter the nuclear forces and the pressure from the reaction once it starts.

All I want to know is if we have a proven net positive model for this reaction because so far I haven’t been able to find one.

Because as far as I know the vital theroem stands so it doesn’t matter if it’s gravitational potential or any other force it still needs to be twice the thermal energy of the reaction.

But you can continue to downvote without actually addressing anything while ingoring everything we know about stellar fusion and the fact that is triggered and constantly maintained by gravitational collapse.

So no I don’t ignore the role of gunpowder in a gun, you ignore the energy needed to create the gunpowder and cartridge in the first place.

That's the best I can do for you. Good luck!

"...the fact that is triggered and constantly maintained by gravitational collapse."

What you have written is not a fact. Forces only do work when they act through a distance. Gravitational potential energy only comes into play during the ignition of a star. After equilibrium is reached, to the extent that the star's diameter is "static" potential energy calculations no longer come into play. No "potential energy" is being "converted" into fusion energy. It's just not a thing.

"...stars are in constant balance between gravitational collapse and their outward pressure caused by fusion."

Because of this balance, no work is being done by gravity. That is, no energy is being released by the force of gravity moving a mass through a distance.

"All I want to know is if we have a proven net positive model for this reaction because so far I haven’t been able to find one."

It's literally E = mc^2, but it's not "net positive." It's net zero. Matter is converted into energy. That's it.

"So no I don’t ignore the role of gunpowder in a gun,..."

It's an analogy, and it's straightforward enough that the onus is on you to work out the pieces a little better than you have. HINT: The "energy needed to create the gunpowder..." is the binding energy in the various nuclei.

>Because of this balance, no work is being done by gravity. That is, no energy is being released by the force of gravity moving a mass through a distance.

I didn’t say it extracts energy from gravity, gravity is constant and it is what keeps the reaction going.

This balance is dynamic equilibrium, gravity continues to counter the gas and radiation pressure of the star’s fusion reaction if you remove gravity from the equation fusion stops because the pressure would cause it to expand until the reaction stops.

If the reaction slows down then the collapse continues until fusion of heavier elements can happen, degenerate pressure can counter it or if neither of those happen you get a black hole.

>It's literally E = mc^2, but it's not "net positive." It's net zero. Matter is converted into energy. That's it.

I didn’t ask you how much energy any given unit of mass has, I asked you for a net positive model for a fusion reaction.

We need to invest energy to make fusion happen then we need to invest more energy to keep the reaction going.

So again I understand where the “excess” energy comes form when two protons fuse into a neutron, however proton fusion isn’t spontaneous and it requires you to expand energy to bring them close enough so they could fuse.

Now in say hydrogen plasma you need to overcome a lot of forces to do that, and more so when the reaction starts since the energy release wants to expand the plasma outwards what I want is to see a net positive model for this reaction.

So far I only hear crickets.

No energy is being continuously invested by gravity. It is not "keeping the reaction going" in that sense. It's simply freshman physics that tells us that forces only do work when they act through a distance. Because the star's surface is not moving inward, it is not doing work, i.e., giving energy, to the star. Furthermore, the Sun, for example, is probably slowly expanding right now. It will start to do so in time, at any rate. That is, the work done by gravity on the Sun will be negative during that time, and fusion will continue. You just aren't making any sense. You are either not trained in physics, or have failed to understand what you have learned. You could begin to piece together a better education in it by simply following up on my replies in this thread. Please, take it from me, you do not know what you are talking about, and your concerns are therefore not valid. I thought I could help, but you seem to be a tough case.

In short: Forces only do work by acting through a distance. Work is energy. If no work is being done, no energy is being produced. Therefore, gravity is not "energizing" the reaction, because the net motion of the star towards its center is zero when it is in equilibrium.

In shorter: No motion => no work. No work => no energy. No energy => no problem.

Again I understand that work (kinetic) is distance over time.

This ain’t what I’m talking about.

The Sun no more extracts energy form gravity to burn than you extract it when you walk but if you turn off gravity then you can’t do either.

The Sun and every other star aren’t static they are in constant balance between their outward pressure and the inner force of gravity, gravity doesn’t just stop when the ignition point is achieved, this is what confines the star and allows the fusion reaction to continue.

Stars have cycles of expansion and contraction and these are understood they are also entirelry governed by the ratio between gravity and their internal pressure fueled by the fusion reaction. So if the Sun expands it means it is generating more energy than what the current gravitational force confines it in, it would expand until a new balance is reached it cannot expand forever unless you turn off gravity and if it would it would very quickly stop fusing elements because it would expand until it cools beyond the temperature which allows for fusion.

Might as well ask where the energy comes from the burn wood - each oxidation has an activation energy which must be paid before the heat from burning is released.

However, as long as the released energy is greater than the activation energy (the reaction is net exothermic), some of the excess energy from each reaction (through heat) goes into powering future reactions. Which is why physicists talk about "ignition" - there's a very strong analogy to igniting a fire with an initial spark of energy.

> So far I only hear crickets.

So far I see lots of people spending a lot of time explaining high school physics to you. Do at least try to be polite while this is going on.

Again you seem miss understand I’m not saying that the Sun extracts energy from gravitational potential but you cannot have stellar fusion without gravity it’s not part of some initial condition that is then irrelevant it’s a constant factor.

A good analogy would be walking it’s very easy to do so on earth under constant gravity but it doesn’t mean that you extract energy form gravitational potential which is when you stand on the surface of the earth is for all intents and purposes zero. However if you switch gravity off you wouldn’t be able to walk.

If we want to simulate gravity in say space there will be an expense to that in terms of say rotating a drum which means we need to expand some energy to do so.

Now with fusion it’s exactly the same we need to bring in the elements into a condition in which fusion can happen and we need to sustain the reaction by not allowing it to expand and cool.

This requires energy so instead of trying to explain me high school physics you might want to answer my original question do we have a model which allows for the extraction of energy form a fusion reaction that does not cool it down until it stops. And does this model including the confinement energy is energy positive or not.

I didn’t asked where the energy released form the fusion comes form it’s a stupid question all energy in the universe came form a single source that is the Big Bang there is no more or less of it in the universe today than there was 15 billion years ago.

Must. Not. Pick. At. Scab...

> Do we even had a model for Fussion that is energy poasitive? The only Fusion reactors we know to work, work by converting gravitational potential energy into light/heat through fusion this is how stars operate.

> All fusion reactions so far require an external input of energy not only to start them but often to sustain them and even those which are self sustaining for a short period of time grind to a halt once you try to extract energy from the system.

That was your original question. It contains, as everyone is aware, your original statement that stars work by converting gravitational potential energy into light and/or heat through fusion. This claim is patently incorrect. It is false. It is misleading. It is a red herring, and a canard. You seem susceptible to it, for some reason. My only advice is to just set it down, over there, and don't play with it. The only winning move is not to play.

> And does this model including the confinement energy is energy positive or not.

Sigh. There is no "confinement energy." This is a physics-sounding phrase that you seem to have coined. Set "confinement energy" down over there next to your original question. It's poison.

> This requires energy so instead of trying to explain me high school physics...

Sigh, again. How much energy, quantified, in the mathematical language of physics and engineering? How much in comparison to the energy released quantified, in the mathematical language of physics and engineering? While these are technical questions, the answer, given by physicists and fusion researchers since well before ITER, is: "We get way more energy out. Full stop. Solved problem. Tokamaks work, with a lower size limited by magnet technology, but not by first law physics. (Implicitly, people who question this at length are cranks.)"

You simply have no basis to go around demanding "a model." If it hit you in the face, you wouldn't recognize it. You, personally, can't quantify this "require[d] energy." You, personally, therefore have no reason, other than obstinance, to think you have some relation between the amount of energy released from a fusion reaction and the energy necessary to create the conditions for fusion. None. No other reason. Pure mulishness. The question is dumb. You are dumber for having asked it, and I am dumber for having read it. It is contagiously, toxically dumb. Please stop. There is no longer any nice way to say any of this to you.

And the one thing you need more of is high school physics, not less.

> ...do we have a model which allows for the extraction of energy form [sic] a fusion reaction that does not cool it down until it stops[?]

Which fusion reaction? Where? So, you can set a solar panel up to do "extraction of energy" from the Sun. Experimentally, this has not shut down fusion in the Sun. So, yes? We have a model? Further, there's no way to not "extract energy" from a fusion reaction, whether or not that "extraction" shuts it down. You, and I, generally exist at a lower temperature than fusion reactions. Ergo, we are extracting energy via radiation from every fusion reaction in the Universe, via heat transfer.

> If we want to simulate gravity in say space there will be an expense to that in terms of say rotating a drum which means we need to expand some energy to do so.

There's a legitimately beautiful and elegant answer to all this energy nonsense in that thought experiment. The answer leads to even more beautiful math about energy, momentum, ground states, and stability. It would be wasted, here.

I'm going to go have a shower, and maybe a drink. This has been an awful waste of time.

>That was your original question. It contains, as everyone is aware, your original statement that stars work by converting gravitational potential energy into light and/or heat through fusion. This claim is patently incorrect. It is false. It is misleading. It is a red herring, and a canard. You seem susceptible to it, for some reason. My only advice is to just set it down, over there, and don't play with it. The only winning move is not to play.

That was a gross simplification but technically correct, without the constant force of gravity which confines the gas there is no sustainable fusion reaction in stars.

On earth we replace gravity with magnetic confinement.

>Sigh. There is no "confinement energy." This is a physics-sounding phrase that you seem to have coined. Set "confinement energy" down over there next to your original question. It's poison.

If I phrase it as the energy required to maintain the magnetic confinement field in a fusion reactor in order to maintain the fusion reaction would it be better? Because now you are arguing semantics.

>Which fusion reaction? Where? So, you can set a solar panel up to do "extraction of energy" from the Sun. Experimentally, this has not shut down fusion in the Sun. So, yes? We have a model? Further, there's no way to not "extract energy" from a fusion reaction, whether or not that "extraction" shuts it down. You, and I, generally exist at a lower temperature than fusion reactions. Ergo, we are extracting energy via radiation from every fusion reaction in the Universe, via heat transfer.

Which is exactly my point the, what confines the nuclear reaction in the sun is a complex process which involves the inward pull of gravity this is what prevents the sun from blowing out until it cools down, you constantly keep ignoring this fact.

On earth we use magnetic fields those magnetic fields require power now I agree that in a reaction that is an equilibrium there is no work between the field and the plasma as both of them are opposing and equal but we still need to power that field if we power it by the excess heat from the fusion reaction the question is then is there any other excess heat that can be used to generate electricity in addition to what is required to power the magnetic field, and this is with a hypothetical 100% efficient model.

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