The sun's fusion is powered by the gravitational attraction of ~10e30 Kg of matter. That is not even remotely an option on Earth, so there is no evidence of feasibility about the energy produced by the sun, aside from the fact that it demonstrates that fusion as a concept makes sense.
Does it tho? Star fusion produces the exact amount of pressure needed to counter the gravitational attraction which is why they don’t collapse or blow up while the fusion reaction is stable, when it’s not the result isn’t pretty.
So in essence stars aren’t energy possitvie (or if so only slightly relative to the energy of the reaction) they just convert one type of energy into another.
This argument makes no sense at all. "Pressure" and "power" don't even have the same units. They are entirely different things.
Let's try to rephrase things in a way that makes physical sense.
There is energy embodied in the Sun. This is the kinetic energy of the electrons and ions that make it up, the energy of the thermal radiation mixed with this plasma, and the (negative) gravitational potential energy.
As the sun formed, energy was liberated by gravitational collapse. This heated up the Sun's material and got things going.
We know (by the wonderful Virial Theorem) that the negative gravitational binding energy of the Sun is ~2 times the internal energy of its particles and radiation.
We can then ask: how does this energy compare to the rate that the Sun is radiating energy? This ratio would give a timescale over which the Sun would cool off, if there was no energy input.
This ratio is on the order of ten million years. But the sun is hundreds of times older than this. So, we can conclude the energy yield of the sun, the ratio of fusion energy output to the initial gravitation energy input that heated it up, is pretty darned good, on the order of hundreds.
The pressure caused by the sun’s ongoing fusion reaction is directly opposite to the force of gravity which constantly wants to contract it, these are exactly equal and opposite this isn’t an argument this is the basis for how stellar fusion works.
∆P · A = −GM(r)m This is the formula.
The sun isn’t powered by the initial gravitational force that heated it up but by the continuous gravitational attraction it experiences all the time.
A star is constantly in the balance between the forces of gravity and the outbound pressure from the fusion reaction this balance is what keeps it going.
So unless you somehow found a way to turn off gravity the sun and every other star in the universe experiences a constant “input” of energy due to gravity.
So the only thing that doesn’t makes sense here is your attempt at physics, hydrostatic equilibrium is what keeps stars going and it’s between the pressure of fusion (or degenerate pressure once fusion stops) and gravity.
> So unless you somehow found a way to turn off gravity the sun and every other star in the universe experiences a constant “input” of energy due to gravity.
The word you want here is "catalyst", not "input". The gravitational pressure has to be there, but it is not consumed.
"The sun isn’t powered by the initial gravitational force that heated it up but by the continuous gravitational attraction it experiences all the time."
This is nonsensical bullshit. Pressure in a static situation does not work, and produces no power.
Maybe you should take a course in freshman physics?
The fusion reaction of a main sequence star is a balancing act between the outward pressure of the fusion reaction (radiation and gas pressure primarily) and the inward force of gravity.
Like this isn't a conjecture we have a very good understanding of how stars work, stars achieve a hydrostatic equilibrium, if they wouldn't they would either explode, collapse or oscillate, the reason why the fusion reaction doesn't cool down is because gravity is constantly pushes the material inwards if it wouldn't the star would expand until the fusion reaction stops and would cool down.
The constant force of gravity is what constantly keeps the a star in a condition where fusion can happen, basically gravity is what is used to overcome the nuclear forces allowing protons to fuse.
"Gravitational collapse is the contraction of an astronomical object due to the influence of its own gravity, which tends to draw matter inward toward the center of gravity.[1] Gravitational collapse is a fundamental mechanism for structure formation in the universe. Over time an initial, relatively smooth distribution of matter will collapse to form pockets of higher density, typically creating a hierarchy of condensed structures such as clusters of galaxies, stellar groups, stars and planets.
A star is born through the gradual gravitational collapse of a cloud of interstellar matter. The compression caused by the collapse raises the temperature until thermonuclear fusion occurs at the center of the star, at which point the collapse gradually comes to a halt as the outward thermal pressure balances the gravitational forces. The star then exists in a state of dynamic equilibrium. Once all its energy sources are exhausted, a star will again collapse until it reaches a new equilibrium state."
Now in fusion experiments we supplement gravity with magnetic fields and pressure from high temperature plasma, but the same thing stands we need to apply constant pressure to allow for protons to fuse into neutrons in order to have hydrogen > helium fusion, not only that but we need to apply even more pressure when the reaction actually happens to keep it because now you have radiation pressure that wants to expand your plasma which would stop all fusion unless countered.
This is exactly why I asked if we have any models which are actually energy positive.
>Maybe you should take a course in freshman physics?
The only way the sun could be powered by gravity would be if it were gradually collapsing. If the radius of the Sun is constant, no gravitational energy would be released. In this situation the pressure in the Sun is not a source of power, any more than the pressure in the tires of your car could be a source of power.
This was actually the theory of how the Sun was powered, a century ago. This caused problems, since the maximum age of the Sun under this scenario is just tens of millions of years, and the Earth was clearly older than that.
We now know the Earth is 4.55 billion years old. The Sun cannot be powered by gravitational collapse, or it would have stopped shining long ago. The pressure and temperature of the core of the Sun set up the conditions in which fusion can occur, but they are not the source of energy that is powering the Sun.
Again do you understand what dynamic equilibrium is? We have awarded a Nobel prize for this, a star is powered by fusion which is maintained by gravitational collapse it collapses to the point where it achieved a hydrostatic equilibrium between the force of gravity and the outward pressure of the fusion reaction that wants to blow it up.
If the fusion reaction overcomes gravity it expands until fusion stops, if gravity overcomes fusion it collapses again until another equilibrium is reached by either fusing heavier elements or through degeneracy pressure, if that cannot be stopped then we get a black hole.
>The Sun cannot be powered by gravitational collapse, or it would have stopped shining long ago.
The Sun isn't powered by gravitational collapse, it's fusion reaction is maintained by it, just like we must maintain a fusion reaction by having the right pressure to allow for proton fusion in the first place and countering the radiation pressure from the fusion reaction which is why we need to constantly supply the reaction with energy to maintain it.
The fact that you still do not accept this is simply mind boggling, consider reading up on hydrostatic equilibrium and stellar nucleogenesis.
"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."
Ironically enough this is exactly with what you've tried to counter my initial post, gravity doesn't go away it is what is keeping the reaction going, if you turn off gravity the gas would cool down due to the expansion and all fusion reaction would stop, but as long as gravity is there the reaction will continue until there is no more fuel to fuse.
"So in essence stars aren’t energy possitvie (or if so only slightly relative to the energy of the reaction) they just convert one type of energy into another."
which is utter crap, at least in the case of a star like the Sun, as I demonstrated several messages back. They are massively energy positive. The fusion energy output is orders of magnitude higher than the gravitational energy that was liberated as the Sun formed.
What confines the fusion reaction and prevents the star to blow out due to the outward pressure from the gas pressure and the radiation pressure powered by the fusion reaction? Basically why isn't a star a giant thermonuclear bomb? This is gravity, yes no energy is technically extracted, but you can no more have fusion in stars without the constant pull of gravity which confines the fusion reaction in the same manner as magnetic confinement fields achieve the same effect on earth.
