Viewing a single comment thread. View all comments

Spiritual_Jaguar4685 t1_iy9gzp6 wrote

To help you understand exactly what happens, you need 4 hydrogens to smash together with tremendous energy, typically due a massive amount of gravity pulling them together.

Each hydrogen atom has 1 proton, but when you smash 4 of them together 2 of the protons "morph" into neutrons. Neutrons are slightly more massive than protons, so all things being equal you can understand why 1 helium should have slightly more mass than 4 hydrogens.

What's also happening is part of that energy in the first place that fused the hydrogens in helium got "solidified" into mass of helium, like energy gets stored in a battery. That energy can be pulled back out if you get the helium atom to decay, this is literally how nuclear energy and nuclear bombs work.

Not sure where you are getting the "more energy" bit from. Either you're thinking about how we can use hydrogen as fuel and not helium (which comes down to electron configurations, hydrogen is "unhappy" and that unhappiness creates a desire to participate in chemistry, hence boom.) Or your thinking of the original energy required to fuse the hydrogens in the first place, and that usually comes from gravity.

3

Lewri t1_iy9q2js wrote

> Neutrons are > slightly > more massive than protons, so all things being equal you can understand why 1 helium should have > slightly > more mass than 4 hydrogens.

Actually, the helium produced in the proton-proton chain has less mass than the constituent hydrogens. The difference is about 23 MeV, which goes into the mass and energy of the byproducts (neutrinos and gamma radiation).

2

TheLapisBee OP t1_iy9izrw wrote

So fusion basically uses gravity to turn mass into energy?

1

Spiritual_Jaguar4685 t1_iy9mcxw wrote

You have it backwards - radioactive decay turn mass into energy. (that's literally what E=mC^(2) means). The conversion multipler of mass to energy is C^(2) so a huge amount of energy makes a teeensy tiiny bit of mass, or a tiny bit of mass makes a HUGE amount energy.

Fusion in stars is complicated, is uses not-ELI5 type things like the "weak nuclear force", and yes, gravity, to convert energy into mass and energy into different mass and energy. The trick in the Sun is it has a tremendous amount of Gravity which kick-starts the process and creates a large net-output of energy (sunlight and other radiation). In something a fusion powerplant the problem is you don't have that gravity source so you need a large energy input in the form of heat in the place of gravity. Currently, it takes more energy for us to create fusion that we get out so it's not a sustaining reaction like the Sun is.

3