Ender wrote: ↑2019-02-10 09:17am
Sky Captain wrote: ↑2019-02-10 05:38am
Not sure I understand, Why would there be so large difference to make 1 kt explosion at target you need to pump out of your energy gun 14 Gt of energy. I know some energy would go into material to flash it to plasma, but at those scales energy to flash few thousand tons of rock to plasma would be relatively minor fraction. When real world nuke explode it also flashes surrounding material into plasma to generate shockwave, warhead itself provide very little material itself. Wouldn't megaton and higher yield energy weapons cause broadly similar effect to a comparable yield nuke when used in atmosphere against ground targets?
Please read the link I included in the post. Most of the energy involved comes in getting the target material up to temperature to mirror the detonation pressure of TNT. High detonation pressure correlates with high detonation velocity, not necessarily with the explosive's total energy, and nuclear reactions have a detonation velocity orders of magnitude greater than chemical explosives.
On reflection, Mike's explanation, while great if you have some basic grounding, isn't the most layman friendly, and I think my connections between my points 1, 2, and 3 is not as clear as it could be
so, basic idea here - how different weapons do things are mediated by immensely different physics depending on the exact weapon, giving them a very different result. The obvious example is a bullet vs a heat ray - the bullet puts a hole in things through momentum and collision physics, the heat ray by calorimetrics. Momentum, energy, power, radiation, heat, pressure, substance, all have a big role to play.
This "things are different" applies even to things that are superficially the same - just because you have two bombs with the same energy does not mean they will have the same results. Before Hiroshima, there had been multiple explosions with similar or greater energy release when ammo ships or armory depots went up. What made the nuclear bomb so shocking and at first unbelievable is that one bomb that small had done that level of devastation.
The way 1 kiloton of TNT, or energetically equivalent amounts of black powder or enriched uranium explode will similarly be very different. This is the designation that makes something a "high explosive", that the detonation velocity and detonation pressure of something like RDX are very high and good for fragmenting the target. For a nuclear bomb, consider the extremely high velocities of neutrons and the very small distance they need to go to react; the effective velocity for comparing them to a chemical reaction is absurdly high. And as I said in 4, overpressure is the most useful for bombardment so it is not surprising that SW energy weapons mirror such explosives in the real world.
Moving to the meta discussion, we are looking to match the visuals as I said in point 2. This gets a bit tricky, as CGI visuals are pretty infamous for not mirroring reality. The example that leaps to mind from the old vs days is that DS9 episode where the Kingons and Romulans bombard the fake Dominion planet, and the shockwaves ripple across the planet at completely the wrong speed. I haven't looked at Rogue 1, but I'd put easy money on the shockwave from the Death Star blast being wrong as well.
Fortunately, we have the non CGI examples to use, some from Rogue 1 but definitely from when the were doing practical effects in the OT and when they were copy-pasting explosions over greenscreen in some of the PT shots. There we know the explosions follow certain consistent physics. IIRC at Hoth the standard SFX explosions was a quarter stick of dynamite with the larger one being a few ounces of TNT (if Wayne is still around I believe he can confirm since that was his wheelhouse back in the day).
So back to the point, this means that we can handwave and say that the properties of SW energy weapons approximate the blast effects of TNT both because it makes sense and because that's what their visuals were, and do some work backwards to get a baseline for the weapon that matches those visuals. Plus if we are talking how they should be, yeah, from what we know having them mirror TNT are pretty effective. Lord knows we've killed enough folks that way.
Keep in mind it won't be a perfect match, and certainly not for all situations. Best we can do is model as many examples as possible and try to figure out a trend line through them, fudging where we must.
There are still some problems with the model - for one we are guessing at the target and fudging some of the inputs because they would be empirically derived and no one to my knowledge has tried to get some of those figures (eg heat of vaporization for granite). On top of that, at high temperatures and pressures these equations break down, and we are doing our best to set a lower limit or order of magnitude estimate. Finally, we don't know key elements, like the application time of the weapons. If a TL needs to apply 6e19 joules of energy in 0.000756 seconds to have a power of 8e22 watts to mirror a 1 kt explosion, but applies over 1 second instead, we need to ramp up the energy applied on the front end. Conversely, if the TL applies at a vastly faster rate than TNT (which wouldn't match visuals but whatever) the energy can somewhat lower.
Modeling orbital bombardment is hard.