61–70 of 73 posts
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Why not launch a probe and point its sensors at earth?
We hardly resolve any individual stars in other galaxies (maybe some giant stars inside Andromeda?), so our idea of chemical composition of other galaxies is very... averaged. We barely can resolve largest and closest exoplanets into a few pixels.
For now...
> There are certain rules that even the most extreme objects in the universe must obey. A strange way to put it. The more object is extreme the harder it would be for it to disobey laws. If we try to imagine what forces are involved, all we'll find is that our imagination has it's limits. I'd be less surprised if some quark disobeyed laws, because it small, forces are minuscule and... who is to notice? Maybe they dis…
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I believe that LHC has no chance ever to harvest enough energy to create a sensible-sized black hole. It’s still mc-squared (give or take an order of magnitude and my layman mistakes), so 1g BH takes about 1e14 joules or 5 minutes of average EU electricity output. Also, there is no sea nearby to cool it off afterwards. Also, a planck-sized BH weighs 1e-5 g. A mass similar to Mount Everest[13][note 1] has a Schwarzsch…
In theory, it might have made a black hole. It would have lasted a ridiculously small period of time, but be quite recognizable by the energy it gave off. Instead of the usual decay patterns, it would give off a spray just of photons, like a black body at a recognizable (and very high) temperature. We didn't see that, and in fact theory predicted that it was insanely unlikely that we would. But there's nothing wrong…
The difficulty in producing a black hole is getting the energy density high enough. We have no known mechanism to get an energy density that's even close the right order of magnitude.
Maybe you meant that in theory quantum fluctuations might do it? Unfortunately, this is really a non-answer. The probability is so ridiculously low that it's not practicably distinguishable from zero. (It's _vastly_ more likely that every measurement ever taken and that _will_ be ever taken is wrong, than that the event actually happened).
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They _do_ evaporate, but they also absorb CMB, and right now CMB > evaporation. Later, when CMB fully dissipated they can evaporate in practice.
> Later, when CMB fully dissipated That's one of the most understated uses of "later" I've heard.
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It _will_ happen, but first dark energy needs to be strong enough to expand the universe fast enough (faster than light) so that CMB wouldn't be able to reach anything.
Well there are already portions of space that are expanding faster than the speed of light relative to our position. (see cosmic horizon). The CMB is not just a glowing heat somewhere far away, it's everywhere in the universe in every volume of space. The moment when every point in space (on a Planck-lenght-scale i guess) will be expanding faster than the speed of light relative to one another, than space-time itself…
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> Later, when CMB fully dissipated That's one of the most understated uses of "later" I've heard.
Hehe, true.
Also, I have a hard time reading that page without a sense of existential dread.
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how can the temperature of a black hole make sense? Is it the temperature of the singularity point? Is it the temperature of the space inside the event horizon (but it can't be, as that space is empty)?
My understanding is it's the temperature of the event horizon: because it doesn't emit any blackbody radiation, other than the tiny amount from Hawking radiation, any heat measurement from it would be approximately 0k.
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Yes, black holes shrink because of Hawking radiation, but in reality this doesn't really happen because black holes are much colder than their surrounding space. Actually they are the coldest objects in nature. Stellar black holes have a temperature of a few Nanokelvins and the average temperature of space is 2.7 K so there's a net gain of energy/mass from absorbed photons from CMB radiation vs emitted photons via Ha…
It _will_ happen, but first dark energy needs to be strong enough to expand the universe fast enough (faster than light) so that CMB wouldn't be able to reach anything.
The temperature of the CMB just needs to drop below the temperature of the black hole.
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We hardly resolve any individual stars in other galaxies (maybe some giant stars inside Andromeda?), so our idea of chemical composition of other galaxies is very... averaged. We barely can resolve largest and closest exoplanets into a few pixels.
>We barely can resolve largest and closest exoplanets into a few pixels For now... https://arxiv.org/abs/1802.08421 https://www.youtube.com/watch?v=NQFqDKRAROI
This also requires a helluva lot of delta-V from the telescope to realign with another planet.
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In theory, it might have made a black hole. It would have lasted a ridiculously small period of time, but be quite recognizable by the energy it gave off. Instead of the usual decay patterns, it would give off a spray just of photons, like a black body at a recognizable (and very high) temperature. We didn't see that, and in fact theory predicted that it was insanely unlikely that we would. But there's nothing wrong…
Do you know what theory that might be? The difficulty in producing a black hole is getting the energy density high enough. We have no known mechanism to get an energy density that's even close the right order of magnitude. Maybe you meant that in theory quantum fluctuations might do it? Unfortunately, this is really a non-answer. The probability is so ridiculously low that it's not practicably distinguishable from ze…
It's just that it's "merely" orders of magnitude. The odds were ludicrously low, but with a whole lot of particles being collided. So maybe, ridiculous outside chance, they might see one event out of the 10^20 events to be observed.
But almost certainly not. So it was never worth talking about. But people loved to talk about black holes, so the math got done.