General Physics Thread

Well, I was thinking that some of their eggs managed to get transported to Earth somehow — like, perhaps members of some other alien race were taking the eggs or even a live specimen to another system for study but had an unexpected accident that caused their ship to crash in a relatively remote area on Earth (in the middle of a big meteorite shower, coupled with solar flare-induced EM interference that messed with radars, radio telescopes and other such devices enough to obfuscate the crashing ship's signature as just another meteorite), with the eggs/specimen surviving the crash and proceeding to start a hive that eventually escalates to a world-threatening Horde of Alien Locusts disaster.

Or maybe the other aliens are using them as Bioweapons to wipe out the dominant civilizations of entire planets without firing a single shot themselves (well, beyond planting the initial specimens), a la one classic interpretation of the Xenomorphs.

But that's off-topic, isn't it? This is the General Physics Thread, and I came here to ask some physics-related questions for my scenario.

Edited by MarqFJA on Aug 2nd 2018 at 7:09:12 PM

Fiat iustitia, et pereat mundus.

Can anyone thing of the practical uses for a pair of magnet like devices that could strongly attract each other from a distance of ten metres but would not affect surrounding metal?

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Maybe if they are used to crush whatever's in the middle?

Are they electromagnets that require a power source to function? Or is it just a natural property of theirs? How strong is the pulling force, and over what range is it effective? I can think of a lot of uses for two objects that are only attracted toward each other. Navigation devices, perpetual motion energy generators, and the like.

Are we getting creative with physics and inventing new forces that don't currently exist? We have lots of fun with that over in the World Building subforum.

OTC is really meant for more grounded conversations.

Edited by Fighteer on Jul 30th 2019 at 4:47:29 AM

"It's Occam's Shuriken! If the answer is elusive, never rule out ninjas!"

I'll post this is world building, but to answer your questions. Only one of the pair requires power, like an electromagnet, the effective range is 2 metres and they range in power the strongest being able to move around 2 tonnes.

Edited by MCE on Aug 5th 2019 at 8:43:07 AM

My latest Trope page: Shapeshifting Failure

What's the reason why the fastest possible speed is light in a vacuum?

Well if you're asking for the reason why the speed of light in a vacumn is what it is... it's due to the magnetic permiability and electric permitivity of a vacumn (or probably more accurately said properties of the underlying space-time... but properly describing that would require a more complete union of general relativity and quantum electro-dynamics. Have fun with that).

As for why... it's how the math for general and special relativity falls out and given that they've been fairly well proven experimentally until someone figures out how to make artifcial wormholes or we actually discover there is some sort of hyperspace or subspace that co-exists alongside normal spacetime where the rules are slightly different we're stuck with them

Edited by KnightofLsama on Sep 7th 2019 at 2:12:09 AM

How much could the cosmic speed limit be modified before it makes life as we know it impossible. Mainly seeing if a universe where superheroes casually go across galaxies in seconds is even remotely feasible to also have life in it

On their own... very little. Changing one or both has knock on effect that would change life as we know it. On the other hand if you change certain other physical constants to counter-act those effect the possibilities become infinite but at which point you need to change everything.

AFAIK there's nothing except what we observe that prevents physics from being classical. Though it would change some things (e.g. black holes would not exist).

Worldbuilding is fun, writing is a chore

Afaik for most natural constants changing them by more than a few percentage points would make the universe uninhabitable. I have not seen any analysis for the speed of light but I think that changing it might destabilize the structure of atoms and perhaps make nuclear fusion overly easy or overly hard.

"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." - Richard Feynman

A lot of those analyses focus on what happens if you change only one or two constants, I've seen larger, more complex simulations that suggest that if you change some variables in other ways to compensate you can bring things back to be similar to our observable universe but you pretty much have to change everything to do so.

These studies are a lot rarer of cousre because you're dealing with a whole lot more variables.

I'll recommend this PBS Space Time video about why the speed of light is what it is. Put simply, the speed of light is the speed of causality. It is the speed at which cause and effect propagate through spacetime.

Light happens to travel at this speed because light is massless. Any massless particle (or force) will always travel at the maximum speed possible and will experience zero time on its own clock. Any particle with mass must travel slower than light, and therefore experiences time. The reasons for this are fascinating and well beyond the scope of a forum post: watch the video for the details.

^note Some particles, like electrons and neutrinos, exchange energy with the Higgs field, which slows them down very slightly, like a form of drag. They experience change, ergo they experience time, ergo they cannot move at the speed of light. Others have mass because they are composites of massless particles with energy bonds that confine them, and the changing configurations of these systems experience time, unlike their individual components.

If the speed of light were infinite (as physicists thought at first), then all things would happen at the same instant. There would be no time at all, and thus no matter could exist.

If the speed of light were faster or slower, then the effect would depend on whether other physical constants that depend on the speed of light also changed. If they kept the same proportions, our universe might be exactly the same. Indeed, in natural units, the speed of light can be expressed as a constant 1, and all other speeds and distances as a ratio of that value. All that matters is those ratios, not the absolute values, if that idea can even have a meaning.

^note Let's say the speed of light were half what it is, and everything else dependent on the speed of light were also half (or whatever they need to be to maintain proportionality). We would be unable to tell the difference, since our measurement systems all depend on these ratios, not on the absolute numbers.

It is hypothesized that there are innumerable universes, each with its own different values for the physical constants. String theory postulates up to 10^500 such possible universes, only an infinitesimal fraction of which would be capable of organizing themselves into something that could support matter, never mind life. This is an idea that we will probably be forever unable to test.

^note  It's also a violation of the Copernican Principle, which states that we should be typical examples of life on a typical planet in a typical galaxy in a typical universe. If there are 10^500 possible universes and literally only one of them could give rise to us, it means we are special, which is illogical.

Edited by Fighteer on Sep 10th 2019 at 10:10:00 AM

"It's Occam's Shuriken! If the answer is elusive, never rule out ninjas!"

Crossposting from the Space Thread:

Ars Technica: Fresh analysis of LIGO data supports “no hair” theorem for black holes

So, how to break this down simply? Black holes are among the most awesome objects in the universe, not least because they prove Einstein's theory of General Relativity to be correct, and further proof came in 2015 when we detected gravitational waves from merging black holes for the first time. They are also fearsomely problematic for quantum mechanics, as GR states that they should destroy quantum information by removing it from the universe.

The "no hair" theorem states that a black hole can be perfectly described with exactly three properties: mass, charge, and spin. Any information about the matter or energy that falls past the event horizon is lost from our universe and can never be recovered, violating a crucial principle of quantum mechanics. Steven Hawking and others attempted to reconcile this problem, resulting in the concept of Hawking radiation and the idea that all of the information about infalling particles remains imprinted on the event horizon and slowly released over the lifetime of the black hole.

The new analysis of public LIGO data from that first black hole merger seems to support the idea that they are beasts of pure general relativity with, indeed, "no hair". This would, if verified (the data are still too uncertain to be taken as absolute proof), be a setback to the potential unification of GR and QM. I'm curious to see where it leads in the future.

"It's Occam's Shuriken! If the answer is elusive, never rule out ninjas!"

A little correction: It's not the absorption of matter by a black hole in general relativity that is problematic from a quantum mechanical perspective.

It's the decay of a black hole by Hawking radiation where the problems begin, since Hawking's original formulation was not compatible with quantum mechanical theorems.

"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." - Richard Feynman

Right, sorry. I oversimplified. The original idea held that Hawking radiation would be a perfect black-body spectrum. This is what would violate quantum mechanics, since the radiation would include none of the quantum information supposedly held in the black hole, and so it would eventually radiate away to nothing, completely destroying that information in the process.

Attempts to explain this resulted in the development of the holographic principle, showing that you could encode all of the information in a black hole on its event horizon, and indeed that the surface of any volume of space can completely describe everything inside. If there is indeed "no hair" on a black hole, then this hypothesis is called into question and we are farther away from a theoretical unification of GR and QM.

Edited by Fighteer on Sep 17th 2019 at 10:05:44 AM

"It's Occam's Shuriken! If the answer is elusive, never rule out ninjas!"

Something to think about: Black body radiation is photonic radiation. But AFAIK there is no physical reason for Hawking radiation to be solely photonic. If it includes neutrinos, protons, electrons etc. that would solve some quantum mechanical problems. OTOH that would create thermodynamic issues relating to conservation of energy and entropy...

"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." - Richard Feynman

The power output in Hawking radiation of a black hole isn't nearly high enough to generate anything other than photons until it hits the very last few seconds of its life.

"It's Occam's Shuriken! If the answer is elusive, never rule out ninjas!"

There are things smaller, weirder and harder to pin down than photons, however... And, we're still running into surprises with the squirrelly photon as it is.

It's black holes: the answer is likely to be both much simpler (and weirder) than we expect, and a bigger, all-new headache to wrap our heads around.

I'm going to contest one thing you said: photons have no size. They are massless, zero-dimensional particles. It is literally impossible for something to be smaller than one. But they are also waves, and every photon can be described by its wavelength, giving it a "size" corresponding to the probability of it existing at any particular location in its waveform. These things are a little fuzzy when you get to the quantum mechanics level.

Speaking of really small things, (Ars Technica) physicists have cut the upper limit on neutrinos' rest mass in half, thanks to new data from the "Karlsruhe Tritium Neutrino experiment (KATRIN)" in Germany. I'm not even going to try to go into the details; read for yourself if you want them.

Put simply, neutrinos are among the hardest particles to detect (and therefore measure) because they are so light and so weakly interacting that they pass through almost all matter like it isn't even there. Billions pass through you every second without affecting you at all. We've known the lower bound of their mass for a while: 0.02 eV, but KATRIN has now given an upper limit of 1 eV, 1/500,000th of the mass of the electron. That's small, yo.

Edited by Fighteer on Sep 19th 2019 at 6:59:38 AM

"It's Occam's Shuriken! If the answer is elusive, never rule out ninjas!"

Something does weird things to photons. Either it's 1) photons be weird like that, 2) there's something smaller than photons or 3) blame other universes for messing with our rules.

You can kind of assign them effective masses in photonic crystals, but they remain quasi-particles at most by virtue of not actually occupying space.

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AFAIK there is no "lower bound" on neutrino masses as such, except for the notion that they should have a positive rest mass. Some theories assign them an exact mass, but these (theory and estimates) are not proven.

"For a successful technology, reality must take precedence over public relations, for Nature cannot be fooled." - Richard Feynman

Of course they're fuzzy, the limits on you're knowledge of their details is bound by the uncertainty principle.

Oh, how I wish I was joking instead of being a smartass.