6 ms·
>Such proximity in mass makes the decay "difficult," resulting in a longer lifetime of the particle, and indeed Tcc+, is the longest-lived exotic hadron found t
by danslo 5y ago
>Such proximity in mass makes the decay "difficult," resulting in a longer lifetime of the particle, and indeed Tcc+, is the longest-lived exotic hadron found to date.
So... how long does it live?
- whatshisface 5y agoThe resonance width is inversely proportional to the lifetime, and if the resonance width is about 400keV, the particle would live for about 10^-21 seconds. For comparison, neutrons decay via the weak force in about 800 seconds, and delta baryons, a randomly chosen strong force decay, live for 10^-24 seconds. That makes this tetraquark long-lived for a strong decay, but that's way, way faster than a weak decay. https://en.wikipedia.org/wiki/Resonance_(particle_physics) https://en.wikipedia.org/wiki/Resonance_(particle_physics)
- Gravityloss 5y agoSo not usable as spaceship fuel
- whatshisface 5y agoIf you're allowed to use something produced in an accelerator as your fuel you can't beat antimatter, which is as stable as normal matter until Kirk orders warp one.
- Gravityloss 5y agoThere's always many considerations. Energy density, stability, what kind of energy can you convert it to, can it be directed easily, how hard is it to store etc...
- whatshisface 5y agoAntimatter's reputation for being incredibly difficult to store comes from the fact that it's produced as individual particles. A superconducting antimatter hockey puck would be much easier to store than a cloud of antiprotons of the same mass. And yeah, you'll need a way to build gamma ray mirrors before antimatter reactions will push you in any direction (the energy comes flying out isotropically and we can't presently do anything to stop or direct it), but we can cross that parsec when we come to it. :-)
- ashtonkem 5y agoGamma ray mirrors sound like they’d be extremely useful for nuclear power too.
- 8note 5y agoSuperconductors pretty notoriously need to be kept cold, which adds another difficulty of cooling the antimatter without touching it
- whatshisface 5y agoIf it was surrounded by a cold mass that it could radiate photons to across a vacuum, its equilibrium temperature would be that of its container.
- kadoban 5y agoFor now. By the time anyone could even possibly create enough antimatter to matter (heh), critical temperatures should be much higher. The record is broken fairly commonly.
- human 5y agoI would be so nervous to be in the middle of space with an hockey puck of antimatter.
- yccs27 5y agoI guess I'd be just as nervous in space with thousands of tonnes of explosive propellant. Spaceflight always operates on the very edge of what's possible, not of what's safe.
- adrianN 5y agoI like black holes because once you have one you don't need an accelerator for refueling. https://arxiv.org/abs/0908.1803 https://arxiv.org/abs/0908.1803
- hnuser123456 5y agoHuh, "black holes move when you push them" is interesting. I suppose you could feed it with a beam, but focusing a beam down to attometer-size beamwidth seems like the hardest part, ignoring making a subatomic black hole in the first place. But sure, I suppose capturing the radiation and redirecting most of it back into the black hole to push it and maintain its size, and just enough spare to push the ship itself at the same speed is feasible. Feels like a "free energy" invention but I don't see where it fails, especially if you could capture the majority of the radiation and feed it back into the black hole directionally, minus whatever used to accelerate the rest of the ship. I see, after more thinking, redirecting the radiation into the black hole would push the ship backwards with equal energy, so half the energy needs to be reflected back into the black hole at the correct direction, and the other half needs to shoot out the back as exhaust, and you'd need additional mass to prevent the black hole from shrinking and getting hotter. They seem to conceptualize a ~100-year black hole which balances semi-feasible mass, power output, and lifespan, which is radius 2.7 attometers, 1.8 million tons, and 17 petawatts (!) of power. Looks like the saturn V was about 50 GW of power, so having ~500,000x the power, with only less than 1000x the mass (2900 tons vs 1.8m), means this thing would propel at hundreds of G's of acceleration, unless the ship itself was another 500 million tons? It looks like the WTC towers were "only" about 500,000 tons, so if you wanted to drop the acceleration to something survivable by humans, you would either need a much larger, colder black hole, or a ship of proportions of 1,000 WTCs. The 10-attometer black hole, with "only" 1 petawatt of power and mass 6.7 million tons and lifetime 5,000 years, seems more reasonable, you'd want a ship with mass 58 million tons to have Saturn V levels of acceleration, only 100 WTCs and the black hole is still only about 10% the mass of the ship. Still, this is only about 6x the width of a proton where we're trying to beam on the order of a petawatt. We would probably need a lot of lasers packed densely together near the back of the ship to focus together on this point to avoid the beam itself being near capable of creating black holes, all coming from the same direction where we need to exhaust equally (or more) as much power to get the ship to keep up with the black hole. Next step would be to figure out how big of a net we'd need to collect enough mass to maintain the black hole but I've spent enough time on this already. Alcubierre drives almost seem more reasonable than this, almost. Oh, and the temperature of this thing would be around a trillion degrees, pretty sure most of that radiation would be gamma rays. Need to figure out how to reflect gamma rays with efficiency. This is apparently around the temperature of a SMBH's accretion disk, the temperature of a new neutron star, and the temperature where matter doubles in mass due to relativistic effects. All this being said, if we can balance the mass of the black hole with that of the ship, with a black hole with lifetime 5000 years, and we achieve 1g constant acceleration, we can cross the galaxy in 24 years and park it for up to a few thousand years before needing to feed it to prevent it from getting too small/hot. https://en.wikipedia.org/wiki/Space_travel_using_constant_acceleration https://en.wikipedia.org/wiki/Space_travel_using_constant_ac... Imagine if you could see the other side of the galaxy and make it back to Earth before you turn 50 (though Earth will have experienced 200,000 years), or, since once you're already at such relativistic speed, see Andromeda and come back before you're 60. Apparently we could round trip to the edge of the (Earth's?) visible universe in right around 100 years. Of course, by time you made it back, Earth would be 26 billion years older, the sun will have exploded, etc. Of course, if these are drone ships, we don't need to worry about human-survivable acceleration, and we could retrieve data much faster, but then no biological lifeform would have been there.
- BurningFrog 5y agoNeeds to be a very short trip.
- phkahler 5y agoAre these decays equivalent to drops to a lower energy state where that energy is mass?
- whatshisface 5y agoThe term "lower energy state" is a funny one, because isn't energy conserved? What's happening is a drop to a more spread out state, where you have several particles making great time flying away from each other instead of one high-energy-density locus in the center. Edit: Just to clarify, the time-variant system exception does not apply in this case. It really is an entropy thing, moreso than an energy thing (which is constant in every particle decay that happens on Earth.)
- MengerSponge 5y agoFun fact: in the most general case, energy is not a conserved quantity. https://www.preposterousuniverse.com/blog/2010/02/22/energy-is-not-conserved/ https://www.preposterousuniverse.com/blog/2010/02/22/energy-...
- debrice 5y agoIsn’t information a better unit?
- thechao 5y agoMengerSponge's article is raising an extremely subtle point about how we translate modern physical theories into English: we do it poorly. Conservation laws (Noether's theorem) are dependent on the way the physics is voiced, mathematically. Saying "energy is conserved" is the moral equivalent of looking at Newton's laws and just ignoring GR. GR tells us new, precise, and amazing things about conservation laws. It's just that, unfortunately, they're a little hard to translate into English.
- whatshisface 5y ago
- im3w1l 5y agoDespite free neutrons decaying in 800s, there are many stable elements containing neutrons. Would it be possible to imagine a tetraquark as an ingredient of a stable particle?
- dukwon 5y agoNo. The presence of a valence antiquark guarantees it will decay at some point.
- evanb 5y agoThat’s not the full explanation; the antiproton is stable (or, is as stable as the proton). It’s that the net baryon number is 0 and that the flavor ‘quantum numbers’ aren’t conserved by the weak force. If you could turn off the weak force, this cc ubar dbar tetraquark would be absolutely stable.
- BurningFrog 5y agoThen I wonder if this "particle" is just some components that takes 10^-21 seconds to bounce away from each other after colliding?
- ShinyRice 5y agoThey don't just "bounce away", some of its quarks turn into different ones through interactions, and that is enough to class that process as a decay. Also, quarks can't bounce away from each other. Lone quarks do not and cannot exist in nature, as far as we know.
- kmm 5y agoFun fact, the reason strange quarks are named strange is because when we discovered the first hadrons containing those quarks, they were strangely long-lived. Long-lived here meaning 10^-10 seconds, instead of 10^-20 seconds. A whole tenth of a nanosecond!
- ansible 5y agoThat is actually quite a long time at the quantum scale.