Ask Anything Wednesday - Physics, Astronomy, Earth and Planetary Science

Submitted by AutoModerator t3_zf37c4 in askscience

Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Physics, Astronomy, Earth and Planetary Science

Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical /r/AskScience post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...".

Asking Questions:

Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit /r/AskScienceDiscussion , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists.

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Past AskAnythingWednesday posts can be found here. Ask away!

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dog_superiority t1_iz9v99c wrote

I understand that if I get in a ship and travel 90% the speed of light, time slows down for me and I come back to everybody else being old as hell.

Yet what about the fact that Earth moving away from me at 90% the speed of light? Wouldn't it theoretically be "returning" back to me, and therefore experience the same slowdown of time?

Or is it acceleration that is important? That since I felt acceleration and Earth did not, that is why my time dialates and the Earth does not?

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Weed_O_Whirler t1_iza1cer wrote

You're correct, it has to do with acceleration. This question has a name, the Twin Paradox and solving this requires a more complex application of relativity than is normally taught until grad school- but essentially, it all comes down the the acceleration.

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willardTheMighty t1_izb9akx wrote

Are there any moons in our solar system which we suspect (or know) have a molten core? Plate tectonics?

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nivlark t1_izc17z4 wrote

Io, the most volcanic body in the solar system. It has a close elliptical orbit around Jupiter, and the changing strength of gravity as it orbits stretches and squeezes the planet, with the resulting friction being able to keep the core molten.

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loki130 t1_izdw0pk wrote

Io has a molten interior but nothing like plate tectonics, magma pretty much just erupts straight upwards through the crust across the surface.

Several other moons like Europa, Enceladus, and maybe Titan are expect to have something like tectonic plates and maybe subduction in their icy crusts, but in detail it wouldn't be quite the same as what we see on Earth, in large part because it's occuring in ice and water rather than rock.

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N-Memphis-ExPat t1_iz9vcnh wrote

So, I understand that a spark, such as lightning or a spark plug spark, is visible because it excites the atoms of the gasses it passes through. Why is the emitted light predominately blue, or is that just my imagination?

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danthedarkness t1_izajelx wrote

The blue comes from the gases in the environment. For lightning and other common sparks, it almost certainly happens in air. The combination of nitrogen and oxygen gives you the blue purple tint. BUT you can see a great example of different colored ‘sparks’ in neon lights! They fill the glass tubes with different gases to get different colors!

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Yaver_Mbizi t1_izaz732 wrote

>neon lights

> different gases

Well... Can't be that different if they're all just neon, can they?..)

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danthedarkness t1_izb1uq3 wrote

So that has been a misnomer for a while now. They used to use neon, which gives off the orange color but has since use other gases to produce the myriad of colors you see.

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camplate t1_izc10p0 wrote

Is there a minimum size for a black hole?

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nivlark t1_izdpr3j wrote

In principle, no. If you can compress any amount of matter within its Schwarzschild radius, it will become a black hole.

In practice, the only confirmed mechanism for the creation of the black hole is the collapse of a massive star, which sets a lower limit of about eight times the mass of the Sun. A black hole of this mass would have a Schwarzschild radius of about 23km.

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DoctorWho984 t1_izg0lg8 wrote

Just adding a couple corrections:

> which sets a lower limit of about eight times the mass of the Sun.

While this is the lower limit for how massive a star must be to undergo a core collapse supernova, the remnant left behind is not the same mass as the entire star, but closer to the mass of the iron core, as the outer layers get ejected in the supernova explosion! Successful core collapse supernovae can explode and leave behind a ~1.4 solar mass neutron star. If the explosion is asymmetric, some of the mass can remain bound to the neutron star and fall back onto it. If enough fall back accretes, the neutron star will no longer have enough pressure support to be able to resist collapse into a black hole. Otherwise, sometimes the supernova fails, leading to direct collapse. With these two routes combined, core collapse supernova potentially make black holes 2 - 100 solar masses.

> the only confirmed mechanism for the creation of the black hole is the collapse of a massive star

Additionally, I think it's safe to say core collapse is not the only confirmed mechanism of black hole formation. There are two other generally accepted black hole formation routes, although they are much less frequent: Accretion induced collapse and neutron star mergers.

In x-ray binaries, material from a non-compact star can accrete onto a neutron star and cause accretion induced collapse, much like the fall back mechanism.

Additionally, neutron star mergers can create black holes of ~2 to 4 solar masses, if the combined remnant from the two of them exceeds the maximum mass of a neutron star.

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slcdmw01 t1_izdgn1f wrote

Most stars are created in open clusters. Open clusters are created from the collapse of molecular clouds. But what creates molecular clouds? Why are molecular clouds often hanging around ready for collapse? Are they just relatively dense parts of the interstellar medium? If so, what makes those parts dense?

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DoctorWho984 t1_izentek wrote

Molecular clouds are thought to be made from overdensities, or filamentary structures, in the interstellar medium where lots of atomic hydrogen is collected. We don't know precisely how these filamentary structures themselves are created, but the leading theory includes contributions from:

  1. Spiral density waves (the same waves that form galactic spiral arms) and other global galactic gravitational instabilities

  2. "Supershells", basically the compression of the ISM by stellar winds, supernovae, and other ionizing radiation.

  3. Turbulent compression, the stochastic movement of the ISM

We don't know the relative importance of each of these processes, but that's the general idea.

[Big ol' review of Star Formation for the brave of heart] (https://arxiv.org/abs/0707.3514)

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slcdmw01 t1_izeuhe7 wrote

Thanks, DoctorWho984! As an amateur astronomer, I am fond of observing open clusters. I haven't found comprehensive answers to this question before -- I learned a lot. And thanks for the Star Formation link.

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ruamru123 t1_iz9vc4n wrote

What would the universe be like if the second law of thermodynamics was the opposite? (it being, somehow, more likely to entropy decreases than increases, a syntropic universe).

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EZ-PEAS t1_iza4krp wrote

Entropy isn't a physical thing, it's a computed quantity that informs us about the state of a system. A decreasing-entropy universe requires some interpretation of what decreasing entropy means in the specific contexts where we talk about entropy.

For example, entropy in thermodynamics means that heat spreads out rather than concentrates, gasses diffuse instead of concentrating, etc. Maybe your interpretation of negative-entropy means that fires suck heat out of the surrounding areas. Maybe it means that gasses concentrate naturally, so if you had a closed box and you left it alone then the atmospheric gas inside would separate into layers of oxygen, nitrogen, etc. by density. Maybe it means that if you shatter a teacup the pieces slowly glue themselves back together.

Entropy is just an observational quantity that describes what we see in the real world. It describes the physical behavior we see in the real world, and the "opposite" of real behavior is not well defined. There is only one realistic, correct behavior. There are infinitely many incorrect behaviors you can pick from.

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davidjara t1_izajt0c wrote

I strongly disagree. "physical things" are precisely "observational quantities" and entropy is just as real as temperature/pressure or whatever thermodynamical quantity.

Going back to OP's question. The only physical law that differentiates past from future is entropy, all other (fundamental) physical laws are time reversal invariants. Many people believe that the passing of time is how we experience a gradient of entropy (Hawking has a beautiful argument of why the only way we can remember something is by increasing entropy in his brief history of time, I can find the exact part if you are interested). From this perspective, it is not that it just so happens that entropy increases with time, it is that we can only remember stuff with less entropy and the stuff we remember is what we call the past.

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MrDownhillRacer t1_izbuq0a wrote

I would think that it isn't too hard to imagine what the universe would be like if all the fundamental dynamical laws were the same, except entropy decreased over time instead of increased.

It would look like our universe in reverse. It would begin from heat death and end in a Big Crunch. Puddles would form into ice cubes. A wave would converge from disparate sources and carry enough energy to eject a penny out of a fountain and into your hand.

I think the difficulty is: can we meaningfully distinguish that sort of universe from our own, or are we just describing the universe we already live in from a different angle? It might be like giving a description of a pencil that starts with its point and ends with its eraser, and then giving a description of an otherwise identical pencil that starts with its eraser and ends with its point. These could just be descriptions of the same pencil.

I suppose there is another ways that you could have a universe in which entropy always decreases. It could start in a state of low entropy instead of with a Big Bang, and just get even lower in entropy from there.

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Mortago_109 t1_iz9y1r7 wrote

When holes distort space time, does this mean they are creating pockets of "different" time? If so, what is it like for two pockets of different time touching each other? Is there a border, or is it a more fluid change?

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mfb- t1_iza7x0h wrote

> does this mean they are creating pockets of "different" time?

No. The rate at which time passes - if you compare different places - depends on the location. As an analogy, if someone in city A earns more money than someone in city B doing the same job then you can see how their accumulated money will differ more and more over time, but nothing dramatic happens if someone moves from city A to B or vice versa.

This is not unique to a black hole, on a smaller scale you have that every time gravity is involved. Even on Earth - GPS satellites take that into account.

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Mortago_109 t1_izaiwd4 wrote

Thanks! It's a fascinating thing to delve into black holes.

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PeanutSalsa t1_iz9ydcj wrote

How much space is there typically between plasma in outer space on average? What's the largest amount of space between plasma in outer space to be detected?

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mfb- t1_iza88ev wrote

There isn't really a "between" as you'll find some ions and electrons everywhere. You can look for the space between particles, or more typically the average density of particles, but that varies wildly.

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SacrificialGoose t1_iz9z9v5 wrote

Is there any chance that over massive time and distance scales the plants, stars, or even galaxies behave like atoms or quarks?

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mfb- t1_iza8gzc wrote

No. This is a very frequent question and you can find many dedicated threads about it. All quarks of a given type are exactly identical and this matters for their behavior. Similarly, we can prepare atoms that are all identical. That doesn't apply to macroscopic structures that are all different. They would not behave like subatomic particles or atoms at all.

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JiN88reddit t1_iza1a2k wrote

Is there such a thing as a universal minimum speed?

We know from Einstein special general relativity that the speed of light is the max speed achievable so I'm wondering if it works the opposite as well. And I don't mean when speed = 0, since that would imply the energy/mass simply does not exist.

The only other thing I can think of is 0 Kelvin, which the lowest possible of energy. 0 Kelvin is also, in fact, also impossible to achieve as well.

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mfb- t1_iza8kpy wrote

0 is the minimum speed. You always move at that minimum speed in your own reference frame.

> since that would imply the energy/mass simply does not exist.

No it does not imply that.

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Luenkel t1_iza6cqu wrote

A speed of 0 would not imply that the object doesn't exist. Where did you get that idea from? All speed except the speed of light is relative and an object is always stationary from its own perspective.

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--Darth-Bane-- t1_izaapvi wrote

Has anything that evolved to multicellular life devolved back to single celled life?

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JimJames7 t1_izabk85 wrote

I once read a comic book series called 'The Ballad of Halo Jones', and in it a war was taking place on a super-Earth called Moab, a planet so dense and massive, that time was severely dilated. (as in, if you were on the surface, a few minutes would last for months compared to somebody in orbit).

Even as a kid I thought this was unlikely, but now I want to ask how far off the mark was it? For instance, if you could somehow survive on the surface of a neutron star, would there be an appreciable difference in the rate of time's passage, compared to orbit?

Here's a pic of the introduction to war on Moab, for anyone interested. The story may have been a bit silly, but the artwork was great; https://1.bp.blogspot.com/-CqeiMUcl8RU/WTJKciJrWkI/AAAAAAAAHRE/w7uWc0s-wpkE1bXjSCX4n9VQNAW1f-HcwCLcB/s1600/halojones8.jpg

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danthedarkness t1_izbwzdc wrote

This happens all the time. It even happens on earth! In simple terms, general relativity describes how gravity curves spacetime, which leads to length contraction and time dilation.

Special relativity describes a similar effect but for fast moving objects.

This effect can be measured for satellites in earth! GPS has to correct for the gravity difference AND the speed difference. The fast speed means time tick slower but the distance from earth gravity means the time tick faster. The total of the two effects is measurable and constantly being corrected. But for earth, the effect is small. Like microseconds small.

But other wise, yes, this is a very possible effect.

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the-nick-of-time t1_izabo55 wrote

Are there any physical calculations that end up with non-integer powers on the units (e.g. square root meters). If so, what's the physical interpretation?

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CrustalTrudger t1_izb72ge wrote

Not sure if this is what you mean, but this ends up being pretty common for empirically derived dimensional constants within equations. As a random example from my field, if you look at Table 2 from this paper you'll see that they're reporting the values and units of a variety of constants for a set of equations to estimate how the rate of rock erosion within a river varies as a function of water discharge (among other things). In there, there are various constants with somewhat nonsensical units, e.g., k_e has units m^(2.5) s^(2) kg ^(-1.5), k_w has units m^(-0.65) s^(0.55), and k_t has units of m^(-7/3) s^(-4/3) kg.

So what does these physically mean? Not much really. These are empirical constants and the units are in effect almost like dummy values to ensure that actual physical values have meaningful units. Take the k_w value for example. This is a constant in the equation w_b = k_w * Q_b^(omega_b), which is relating the bankfull width of a river (w_b) to the banfull discharge (Q_b) as a powerlaw. You'd get the value of k_w and omega_b by fitting observed values of width (in meters) and discharge (in m^(3)/s) and thus the units on k_w will depend on the best fit power law exponent (omega_b) and be appropriate to make sure that when you raise discharge in m^(3)/s to that power and multiply by k_w, you get width in meters.

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dogCerebrus t1_izacr6o wrote

With Nasa making some strides in sending a "message" between 2 virtual wormholes it got me thinking again on Alcubierre and his famous paper. One of the biggest challenges to warping space-time is the enormous energy requirements and the use of exotic negative mass particles. A while ago however i believe a new paper was released that brought the necessary power requirements down to some significant percentage of the suns output.

My question is, if we could somehow generate the necessary energy tomorrow. Could we warp space-time even on a small scale? Do we know what the physics or engineering requirements are to warp space-time? Or is it just a matter of dumping enormous amounts of energy into something like a magnetic field

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Trouthunter65 t1_izajjjo wrote

What do we need to be able to control gravity here on earth? Do we need more information and understanding or a completely new element etc. Are people actually working on this or are we resigned to the idea that gravity is what it is and we need to live with it.

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loki130 t1_izdwcd6 wrote

There is at present no theoretical basis for the manipulation of gravity other than through the presence of mass-energy (i.e., how gravity usually works).

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Foxybabe21 t1_izakpyb wrote

I've listened to Peter Ward talk about the rare earth hypothesis before and have done some brief reading on the subject. With what we've learned since that book was published (2000) through the various new telescopes and other means, does that hypothesis seem closer to the truth or further away?

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loki130 t1_izdwoi8 wrote

We really don't have near enough information to have any uncertainty about it. Perhaps some more extreme claims about the occurence rate of roughly earth-mass planets in inner planetary systems have become implausible, but we know very little about what the surfaces of these planets are like or what conditions are necessary for life.

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Barreling_Burke t1_izalhkb wrote

My science question; how do we know the 3 UAP videos released by the pentagon in 2017 are legitimate or illegitimate? I’d like to be able to say with confidence that we have recorded objects defying our known laws of physics, but has hard data/proof been accepted by the scientific community in large?

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ieatdirt44 t1_izam4bn wrote

I've seen many depictions of black holes looking like a funnel, a heavy object on a trapoline or studied using water to create a vortex. All the depictions make it seem as if the event horizon is on a singular plane. How accurate could this be for actual black holes? I picture in my head, a central point or singularly being in one static position while the space around it is warped from every possible direction creating infinite vortices all being "stretched" (down?) Towards the singularity.

I guess my question is: Do we need to think in higher dimensions to be able to understand black holes and is it feasible that humans will ever one day be capable of imagining and comprehending anything but the 3 spacial dimensions we've been adapted to believe?

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opiateopiate t1_izbo520 wrote

Those depictions offer an analogy for how massive objects warp spacetime that's easier for us to picture than the reality, which is a four-dimensional manifold being squeezed, stretched, and warped by those objects' gravity. A sheet of fabric is two-dimensional, so showing it "stretched" into a third dimension demonstrates gravity's action. You're right in thinking that we would have to be able to think in five-dimensional terms to envision the action of gravity on spacetime in a similar way, since spacetime is four-dimensional.

Humans as a whole probably won't get better at getting intuitive feels for high-dimensional spaces and manifolds. 3D is "baked in" to our perception of the world and our internal model of how it works and how to move through it. Mathematicians often do get slightly more of an intuitive sense from working with them long enough.

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Ecl1psed t1_izatrna wrote

I am having trouble wrapping my head around how it's possible that there are no local hidden variables in quantum mechanics. I came up with this argument that seems to me to be solid, but it would contradict the nonexistence of local hidden variables. Could someone point out where the argument goes wrong?

Suppose Alice and Bob take two entangled particles very far from each other. For simplicity, assume they are 1 ly apart, and with a relative velocity of zero. Suppose the particles become entangled at year 0.0, and Alice and Bob take 5.0 years to reach the 1 ly mark.
When I talk about "before" and "after" in this argument, I am referring to the reference frame of a point exactly in between Alice and Bob, also with a relative velocity of zero.
Suppose that the particles are entangled in the Bell state, so that A's and B's measurements will always produce the same binary result of either 1 or -1.
Without loss of generality, let's say Alice gets a result of 1. Now, Bob is guaranteed to measure 1 as well. This is true matter how long he waits. He could wait until year 50.0 and he would still get a result of 1. Consider two scenarios:
(1) Alice mesaures at year 10.0, and Bob measures at year 10.5
(2) Alice mesaures at year 10.0, and Bob measures at year 9.5
From Alice's perspective, there is absolutely nothing different between the two scenarios. In either case the no-communication theorem prevents any information from being transmitted, since they measure only 0.5 years apart. Thus, she will measure 1 in either scenario.
Now, consider a third scenario:
(3) Alice mesaures at year 9.0, and Bob measures at year 9.5
From Bob's perspective, this scenario is identical to the second scenario (due to the no-communication theorem), so he (and by extension Alice) is still guaranteed to measure a 1 in this case.
Now, consider a fourth scenario:
(4) Alice mesaures at year 9.0, and Bob measures at year 8.5
Again, from Alice's perspective, this is completely identical to the third scenario, so she (and by extension Bob) will end up measuring 1.
You can probably see where I'm going with this. We can follow this logic all the way back to the creation of the entangled pair. The conclusion of the argument is that if Alice measures a 1, then it must have been the case that measuring the particles at any previous point (after they were entangled) would also have resulted in a 1.
This seems to me to force the existence of a local hidden variable. Apparently this isn't right, because we have recently ruled out local hidden variables from being consistent with observations, but I am at a loss to see what is wrong with this argument. Or is what I said correct, but there is another explanation for it without involving a local hidden variable?
Could someone explain what is the issue with this argument? And, could someone explain Bell's theorem/Bell's inequality in layman's terms, and how it's possible that QM can violate it?

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SonOfOnett t1_j22snxg wrote

The problem with your argument is you are saying Alice is going to measure a 1: that’s a hidden variable you are introducing into the thought experiment! In reality and experiment, regardless of who measures first, we don’t know what the outcome of that first measurement will be.

You need to stop after stating that Bob and Alice’s particles are entangled to have the same measurement. Given that, neither observer, no matter how close in time to the start of the entanglement will know what they are going to measure, just that their measurements will match.

Veritasium has a decent video on Bells Inequality that may be useful to you as well. It explains how we can tell the difference between a local hidden variable or not

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Ecl1psed t1_j24gd5s wrote

I assumed that Alice measures a 1 because the argument would be the same no matter what she measures. Just replace the 1 with -1 and the logic still works. (Basically, "without loss of generality"). Or, I could have some variable X that represents Alice's measurement. We don't know X until Alice actually performs the measurement, but I think the argument should still work if we just replace all instances of 1 with X. I'll have a look at that Veritasium video, thanks for mentioning it.

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alittlebitaspie t1_izava1z wrote

So in space around earth the sun heats everything to a ridiculously high temperature. How far away would you have to go from the sun for that temperature to be comfortable for humans (say about 90 F/32 C)?

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TwentyninthDigitOfPi t1_izb2jsz wrote

Would it be possible to harness dark energy to leave a black hole?

My understanding is that dark energy is the current "fill-in" to explain why the universe is expanding. Farthest away from us, that expansion is faster even than the speed of light, due to the cumulative effect. So, if we stipulate (a) that dark energy is indeed the cause for this expansion, and (b) that we can manipulate it to expand pockets of the universe at will, then would we be able to use that to essentially expand our way out of a black hole? I'm imagining a craft that could expand space behind it (closer to the singularity) and essentially ride that expansion to get out of the event horizon, without ever having to travel faster than light in its local patch of space.

I realize that "could we do this thing predicated on unknown physics" is a bit of an impossible answer; so I guess what I'm really interested in is whether the math of current theories would allow for such a thing, assuming the two stipulations above.

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davidjara t1_izbidwk wrote

Long story short, no. Dark energy is the energy of space itself. We cannot move it/compress it/manipulate it in anyway whatsoever. If I understood your idea correctly you want to put a lot of dark energy in a tiny space and see what happens. This is like asking if you can put a big chunk of space in a little space.

I want to stress that even though dark energy is code term for "weird energy of empty space we don't understand anything about" by its very nature, it cannot be manipulated and hence dark energy BH are simply not possible.

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TwentyninthDigitOfPi t1_izbk5jp wrote

How certain are we of that? Just from reading wikipedia, it looks like some models of dark energy are compatible with what you said (e.g. a cosmological constant), but other models seem to be more "normal" kinds of energy (like quintessence).

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davidjara t1_izbrmp2 wrote

Certain beyond reasonable doubt. Let me first say that the cosmological constant is not a model of dark energy. The cosmological constant is a low energy, effective description of whatever dark energy really is.

Dark energy is the term coined to describe the accelerated expansion of the universe, most people (myself included) believe that this is due to vacuum energy. The quintessence story is a way of explaining the expansion, not as vacuum energy, but as interactions with a field. This field violates basically every single reasonable expectation (that's why not many people like it) and (to my knowledge) it barely works even in the simplest situations. If the expansion of the universe is due to a field like in the quintessence story, then it's possible you could something with it. However, you will struggle to find a single researcher that believes the expansion of the universe is due to something different that vacuum energy.

So just to put a bit of salt on it. My answer was regarding the energy of empty space. I believe that beyond any reasonable doubt dark energy is the energy of empty space. If this is true, there is no way to make dale energy BH. On the other hand, if it turns out that the universe expansion is due to some matter fields then you could in principle build stuff with it (like BH).

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CovenOfLovin t1_izb9d6h wrote

Why do many believe a naked singularity would bridge the gap between relativity and quantum mechanics? What do we expect to find if this is plausible?

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willardTheMighty t1_izb9guc wrote

What is the scientific consensus on whether or not Mercury is tectonically active? Venus?

Are there any other bodies in our solar system that are tectonically active?

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clintontg t1_izb9gyk wrote

When it comes to field theory and high energy physics, is it accurate to consider quantum fields as fundamental and particles as energetic perturbations of those fields?

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davidjara t1_izbitv9 wrote

Yes. the maths is pretty straightforward, fields are the fundamental stuff and we see particles when these fields are excited.

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willardTheMighty t1_izb9jc9 wrote

What are your thoughts on the Planet 9 hypothesis?

If it were discovered, what would your vote be for its name?

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juanpontoon t1_izblhah wrote

Is it the case that a candle lit in zero gravity (like the space station, with Earth-like atmosphere) would have a briefly spherical flame which would then burn out from oxygen deprivation? Heat rises and without gravity, would it not expand spherically, and then there would be no adjacent oxygen? Thank you.

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Triabolical_ t1_izcz7lb wrote

Yes, assuming there are no air currents.

ISS has ventilation always running to keep the astronauts from building up carbon dioxide around themselves.

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juanpontoon t1_izfnou6 wrote

That is so cool! Thank you. I've asked this question for years, had my own hypothesis, and never a chance to test it.

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warrant2k t1_izbn2d6 wrote

What are the differences/concerns of a nuclear reactor operating on the moon vice on earth. Does the moon's exosphere require different technology of operation? Would the cold temperature be sufficient to cool the rods?

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nivlark t1_izc2ga8 wrote

No, you still need a fluid to carry the heat away. Assuming the point of the reactor is to produce electricity, water would still be a natural choice because it turns to steam which can then be used to drive a turbine.

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Triabolical_ t1_izcz3ny wrote

Cooling is very hard in space because you can't use conduction or convection, so all you can do is use radiation.

NASA has a project named KiloPowerthat is working to build reactors for the moon and mars.

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Be_Cool_Bro t1_izboo4e wrote

Probably several misinterpretation on my part, but here goes.

I keep hearing the faster something goes the faster time goes relative to its point of view. And I also keep hearing space and time are inextricably intertwined as spacetime.

So, where does the space part fit into that phenomenon? Does acceleration or lack-thereof of an object make it experience more or less space at any singular frame? Is my question completely nonsensical?

I only wondered this after seeing an explanation that says an object going at the speed of light wouldn't experience any time, so I wondered about the space part.

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nivlark t1_izc6htj wrote

An observer always measures their own time to be normal, but will see time running slower for a second observer who is in motion relative to the first. And this is reciprocal: for the second observer, their time is normal and the first observer's clock is running slow.

Space has to be involved because otherwise there are contradictions: consider observers A and B, where A is stationary on Earth and B is travelling at high speed to a distant planet. A will measure B's journey to take a certain amount of time, but because B's clock is running slower, they would conclude that the journey took less time.

If both observers were to agree on the distance B had travelled, then they would have to disagree on their speed. The solution is that they don't agree on the distance: not only does time run slower in moving reference frames, lengths are measured to be shorter. From B's perspective, the planet is approaching them and so the distance to it shrinks. Their clock measured fewer ticks, but the distance they travelled is also less, and so they can still agree with A about their speed.

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InfernalGriffon t1_izc59hj wrote

If a black hole composed of antimatter collided with a black hole made of matter what would happen next?

Also, could antimatter black holes be a possible answer for why there's so little observable antimatter in the universe?

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nivlark t1_izdqalj wrote

Nothing special: black holes are believed to obey something called the "no-hair theorem", which states they can be completely described by their mass, electric charge, and angular momentum. So there is no way to tell, at least from outside the event horizon, whether the black hole formed from matter or antimatter.

As to the second question, the mass in black holes that we know of is only a small fraction of the total mass. So there is no evidence for a large population of (ex-) antimatter black holes.

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JuliusHibbert t1_izcb3mc wrote

Dk anything about physics, prob a stupid question:

Is the universe many separate things, or one giant thing?

Like is space-time a separator, or everything connected by the fabric of space- time?

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ShacklefordVsSeagal t1_izcvh4d wrote

Why couldn’t we honor use a giant tube to harness the vacuum of space to create a interplanetary transport system for goods and travel? All logistics for the tube aside.

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loki130 t1_izdxhmq wrote

A tube to space isn't going to pull up objects any better than the vacuum of space pulls up objects anywhere else on the planet, if that's the idea here.

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brjgto t1_izd01gu wrote

I’ve wondered if ANYTHING man made, other than rockets have left earths grasp. I.E. Can a bullet be fired fast enough, or a jet with A/F mixture climb fast enough to leave earths gravity and never return? Why or why not is this possible? TY

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toxicpsychotic t1_izdtima wrote

Fritz Zwicky's "artificial meteors" might count. Though they were launched from a rocket, it wasn't a rocket capable of reaching orbit; the pellets were launched away from the rocket by an explosive after it reached the upper atmosphere.

It's believed that they escaped earth's gravity well and went into orbit around the sun. There's no real confirmation that they did, but it's certainly possible.

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4hexa t1_izd73l8 wrote

What are the types of enrichment methods of rare earth elements? I cannot find any general explainations but specific ones.

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ankitgusai t1_izd7rb7 wrote

If we were to figure out that a small fast moving black hole is passing by solar system (say closest approach will be 1 light year away) what would be some of the most interesting science we can do?

With limitations of current tech would we even be able to send a prob somewhat closer to the BH? Or we will be limited to distant observations only. Would a special telescope make sense? (dedicated 100% to the BH observations).

Thanks.

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tauofthemachine t1_izdh5qy wrote

I've always heard that black holes slowly "evaporate" in Hawking radiation over an astronomical long time, but I also heard that time slows down in gravitational fields.

So could a black holes slow hawking's radiation just be an explosion, which is "slowed down" by the black holes gravity, so from the outside it seems to be exploding "really really slowly"?

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