Anyway, in a recent thread about antimatter weaponry, Astro* noted that:
:eek:
(Actually, that’s about 500 megatons, by my figuring, so a matter-antimatter reaction would be twice that. But still…)
However, I’ve run the 1 Gigaton number through a couple of calculators (The Nuclear Weapon Effects Calculator, Solar System Collsions and the lovely Earth Impact Effects Calculator) and none of them are predicting an Extinction Level Event. However, the first is for estimating the effects of a nuclear weapon, not an antimatter explosion—the effects of which I don’t know if would differ dramatically than a nuclear fusion explosion of the same yield—and the last two (even the Impact Effects Calculator, which provides a LOT of welcome details), were based around the estimating the effects of an iron asteroid impacting the Earth, not an airburst at an altitude to maximize destruction.
And, y’know, they’re all free web calculators, so it’s not like this is information from a Cray at Lawrence Livermore.
So, I’m asking…just what, roughly, would a 1000 megaton matter-antimatter explosion do to the Earth? Planet-killing catastrophe, or just a really big “bang”?
*By the way, Astro, I reeeally hope you don’t mind my quoting you, here.
As was noted in the previous thread, a 1000 MT H-bomb would be larger than anything ever tested, but it isn’t massively larger than the Tsar Bomba that the Soviets exploded in 1961. This had a design yield of 100 MT, but was reduced to 50 MT for the test.
Setting off something 20 times larger may sound like a whole new ball game, but it actually isn’t, since the various types of damage from a nuclear explosion only scale as fractional exponents of the yield W. Thus, for example, the size of the fireball roughly scales as W[sup]0.4[/sup] and the pressures as W[sup]1/3[/sup]. So a 1000 MT bomb would only be about three times “larger” than the 1961 test.
The more delicate question is whether a 1000 MT nuclear weapon is the correct comparison for the hypothetical antimatter bomb.
Most of the energy in a nuclear weapon (either fission or fusion) is initially in the form of kinetic energy of the atoms, with only a relatively small amount being carried away as photons (or in the neutron radiation). That kinetic energy is then converted into the fireball and blast effects. That mainly happens by what’s effectively a high temperature gas radiating and that radiation driving these effects.
By contrast, our hypothetical antimatter weapon initially produces nothing but photons. However, these photons are actually of significantly lower energies than the energies involved in the fission and fusion reactions above. (Typically, a fission fragment starts by carrying roughly 100 MeV, while the photons in the antimatter bomb initially have 0.5 MeV. About the same as the prompt gamma rays in a fission weapon.) But this is comparable to the temperature of the radiation produced from the energy lost from the fission fragments.
The results are thus likely to be rather similar.
The “Megatonnage” is the explosion’s equivalent amount of TNT. So, a 1000 Megaton antimatter explosion would be exactly the same as a 1000 Megaton fission explosion or a a 1000 Megaton TNT explosion - you’d just need much smaller amounts of anitmatter to produce that explosion.
A billion tons of animatter annihilating with a similar amount of matter would produce a 10[sup]plenty[/sup] Megaton explosion which would undoubtedly blow the planet to bits.
Blast effects tend to scale with the inverse cube law, thermal effects with the inverse square law. In general, really big bombs (Tsar Bomba - 100 MT), are a waste of resources. You could cause far more destruction with 100 one megaton bombs.
For the hypothetical 1000 MT bomb, how much of that energy is going to just be radiated out into space in the form of thermal radiation?
Depends on the antimatter. If it’s an electron/positron bomb, your initial product is gamma radiation. As these rays are absorbed by the surrounding atomosphere, the air is super-heated, and you get a fireball. If you used a proton/antiproton bomb, most of the energy produces neutral and charged pions, the former decaying into gamma photons, the latter having a relatively messy decay cascade that would produce things like electrons and neutrinos. In fact, much of the energy would be “wasted” as neutrinos (which hardly do anything to surrounding matter), but hadrons pack a lot more matter/energy into a small space than leptons.
The Tsar Bomba, at full yield, would completely flatten everything for 20 miles around, and mostly flatten everything else about 8 miles beyond that. Whatever isn’t also flattened will be immolated out to almost 50 miles. Crazy.
According to this helpful site, you would need 1,300,000,000,000 metric tons of antimatter to destroy the Earth. Of course, this guy is talking about doing a thorough job, here … if you don’t mind the shattered fragments of the planet gradually coalescing into a new globe, you could probably make do with less.
