Posts by HDE 226868
The simple answer is a no. We've gotten some pretty good constraints from the Planck satellite; their final results indicated a dark energy density of $\rho\approx6\times10^{-30}\text{ g cm}^{-3}$....
Orbit, rotation, mass and other properties not directly related to life A planet is a rotating mass (larger than ~500km in diameter) in orbit around the star of normal material becomes an oblate s...
The question: What characteristics are necessary for a planet to be habitable for humans? What should the generic star and planet be like? The life forms are human, so they Need to have access ...
Age: The time a star spends on the main sequence is roughly inversely proportional to the luminosity, as given by the formula $$T \approx \ 10^{10} \text{years} \cdot \left[ \frac{M}{M_{\bigodot}...
The question: What characteristics are necessary for a planet to be habitable for humans? What should the generic star and planet be like? The life forms are human, so they Need to have access ...
Directly? No. Indirectly? Yes. As Renan indicated in their answer, material that enters a black hole cannot leave; the only way around this is through evaporation. Even then, the Hawking radiation...
The Copernican principle As L.Dutch pointed out, this would violate the Copernican principle, which essentially states that there's nothing special about observing the universe from any one place....
This is actually a really interesting question. While there are many stars with orbits outside the galactic plane ("halo stars"), these tend to be old and metal-poor, as star formation in the halo ...
The Alcubierre drive not only allows but actually necessitates the production of event horizons at superluminal speeds - but not necessarily the sort you're looking for. It's been shown (Finazzi e...
The Alcubierre drive works by distorting space around a bubble: expanding space behind it and contracting space in front of it. It's a nice way to get faster-than-light travel without, well, techni...
The big problem with using radar in outer space is simply range. The received flux of a radar signal falls off as $1/r^4$ instead of the $1/r^2$dependence we're used to getting for signals emitted ...
This answer is meant as a supplement to notovny's. I agree with their conclusions (the scenario is impossible because of the instability of this Lagrange point, and the fact that the Hill sphere is...
This wouldn't work. The big issue is that stars make up only a few percent of the Milky Way's total mass - estimates vary by a bit, but I've heard numbers in the 3-5% range. For instance, McMillan...
Simulations of the dynamics of planets close to massive stars during a supernova (Veras et al. 2011) indicate that a planet in a reasonably tight orbit ($\sim2\text{ AU}$) around all but the lowest...
I agree largely with Matthew's answer; this is intended to put everything on a more quantitative footing. The answer to your question primarily depends on three things: the mass of molecules in th...
Sort of. A structure similar to the one you describe can in fact form. Triple-stranded DNA can be stable under certain conditions. Two bases bond via slightly different structures, and a third bas...
Sure. Not a whole lot, but you'll get a decent number. Beer et al. 2004 present a formula for calculating the mean time before a star passes within a distance $b_{\text{min}}$ of another star: $$...
Just reduce the rate at which you lose entanglement (The paper, for anyone wanting to read it, is Humphreys et al. 2018.) The hey problem here isn't entangling particles, per se - the problem is ...
Based on the current state of thinking, somewhere in the vicinity of a couple hundred kilometers. This particular formation theory (Zhang & Lin 2020) is a variant of an idea that's been kicked...
A decent proxy for habitability and long-term colonizability is the effective temperature of the planet - essentially the surface temperature. A planet's effective temperature scales as $T\propto (...
Try microlensing other evaporating black holes Folks have suggested Hawking radiation; I don't think that's a particularly good idea. If you run the numbers, a black hole would need to have a mass...
It would be uniform. The crust of the Moon is, on average, about 50 km thick. There is indeed some stratification in its composition, with upper layers composed largely of feldspar and a lower lay...
A cosmic void. Your best bet would be in a cosmic void. While not entirely empty - they do contain small numbers of galaxies and clouds of gas - they are substantially rarefied compared to your av...
The best tools for this job, I think, are perturbation theory and Laplace's planetary equations. You might know that the orbit of a planet can be described by six osculating elements $(a,e,i,\omega...
At least on Earth, astronomical instruments are extremely precise and sensitive compared to the innate biological abilities of an astronomer! Sure, I can look up at the sky and see that Betelgeuse ...
