There are a couple of different potential outcomes, and there are examples of pretty much all of them in some places. If the ridge is roughly parallel to the subduction zone:

1. Option 1 is that the ridge doesn't actually subduct because subduction stops before the ridge gets there. Effectively the idea is that subduction is driven by the negative buoyancy of the subducted slab, which is a function of the age/temperature of the slab. The piece of lithosphere adjacent to an active ridge is pretty warm, young, and positively buoyant so it will resist subducting. Depending on the relative competition of forces what may happen is that subduction slows down as this young lithosphere approaches the ridge (resisting subduction) and then the slab rips off (i.e., it detaches) because the slab pull force overcomes the strength of the slab nearer the surface. This can effectively terminate subduction (no slab pull = no subduction). As to what happens from there, it will depend on the specific forces, but most likely the ridge might die and there will be a general reorganization. That reorganization might see a wholly different set of plate boundary kinematics or the subduction zone might "jump", keeping effectively similar broad scale kinematics but with the subduction zone in a different place. It might also jump and reverse polarity.
2. Option 2 is the ridge subducts and the slab detaches because there's nothing really connecting the other side of the ridge to the slab. The end result of this proceeds largely the same as above.

In terms of these geometries, the basic assumption was effectively option 2, but in detail, it's actually hard to get a ridge to subduct and option 1 is more favorable (e.g., Burkett & Billen, 2009). Semi-parallel ridge subduction does happen though, and for it to happen, usually some amount of complicated geometries and "3D effects" are required (e.g., Burkett & Billen, 2010).

If instead the ridge is very oblique or orthogonal to the subduction zone, the ridge will subduct and in many cases a "slab window" will open along the subducted segment of the ridge. You can picture the ridge effectively unzippering down the length of the subduction zone, kind of like this. This makes some specific predictions about what you would see in the upper plate, specifically a gap in normal arc volcanism and instead magmatism that is more indicative of direct mantle interaction with the upper plate rocks.

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I think you're confusing anti matter with dark matter.

But for dark matter you're pretty much right. For example, we can see things orbiting with some speed and can deduce the mass needed for such an orbit. The mass of stuff we see is mich smaller than the needed mass, so apparently there is some stuff that is "dark", i.e. doesn't shine or reflect light, also doesn't absorb. More like glass in this respect, or air. The light just doesn't care about it being present. So physicists started calling it "dark matter" as it doesn't shine, plus it fits well with the fact that we don't know yet what it is.

That's not anti matter. It's dark matter. And if it was anti matter then we wouldn't exist at all. And yes we don't know what it is.

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From either ship's perspective, the Earth is approaching (at the same speed an observer on Earth measures the ships to be travelling at), and the other ship is approaching at a slightly faster speed (which you can calculate with the relativistic velocity addition formula).

But from the ship's perspective, the distance from it to the Earth at any given time is smaller than the distance from the Earth to the other ship. The other ship is approaching faster, but it has more ground to cover. These effects cancel, and the two ships arrive at the same time.

> From each's perspective they should arrive at Earth first

What would happen if the winner grabbed a trophy (or whatever) on their way by? Relativity can break simultaneity, but not cause & effect. Thus "local" simultaneity must still be preserved in all reference frames. It's only distant events that different reference frames will disagree on.

> From each's perspective [..] the other would appear to not be moving at all

This would only be true if they're moving in the same direction. But in that case, they can't both be heading towards Earth.

There are a bunch of factors. One of those though would be the ocean, which does take longer to change temperature.

It's largely down to heat capacity, mostly that of water. Water requires a good bit of energy to heat up by a given amount, and it has to lose that same energy to cool down; so even though the amount of solar heating is lowest in December, the oceans and other bodies of water are still holding onto heat from summer, and will continue to cool until the rate of solar heating surpasses the rate of cooling at some point in spring.

Heat is distributed pretty widely in the atmosphere, the poles are a fair bit warmer than they would be without an atmosphere and oceans, but the transport still isn't perfect so there is a gradient (compare to somewhere like Venus, which has a thicker atmosphere of mostly greenhouse gasses and so very little temperature variation on the surface, other than that caused by altitude).

If you can make microscopic black holes then you can extract some energy (but nowhere close to a star). Otherwise the radiation is completely negligible. A black hole with 2 times the mass of the Sun (around the smallest black holes we know to exist) has a power of just 2*10^(-29) W.

To get a power of 1 MW you need a black hole with a mass of just ~10^10 tonnes (emissions would be gamma rays and electrons and positrons). These still live longer than the age of the universe so they might exist as primordial black holes but we have never found one.

A black hole with a luminosity similar to the Sun would evaporate in around a microsecond.

You can feed the black hole with matter and extract energy from the radiation emitted by the accretion disk. This is a very efficient process, better than fission or fusion, and you can use random waste as fuel.

This also has a lot to do with distance - relatively speaking Mars and our own Moon are very close to Earth. The moons of Jupiter and Saturn are incredibly far and the logistics of keeping people alive on those moons is beyond our current capabilities.

Even a Mars colony - a true one with humans constantly inhabiting it - would be incredibly difficult. If anything goes wrong, human lives will be lost without question. It is more likely that a Martian base would be first established as a research outpost, only housing humans on explicitly research-focused missions.

Source: I'm an astrobiology PhD (fifth year) at McMaster University.

First of all "seriously considering" just means " people are talking and writing about it" not anything concrete.

But even floating on Venus has advantages over gas giants. You have much higher gravity on gas giants. It is much harder to launch out of the atmosphere. The hydrogen helium mix is worse for bouyancy. The planets are much further away. And there is no altitude with decent pressure and temperature.

The energy to get to Mars and Venus is much, much less than it takes to get to the gas giant moons.

Can't speak to what you're talking about, but there are definitely well preserved examples of other organisms such as those from the Cambrian explosion in the Burgess Shales, or the fishes and archaeopteryx found in limestone. Crinoids, afaik, still exist and have existed for a long time. It is likely the ones you've seen are relatively young and we're preserved through other methods. 3D fossils typically form due to replacement of the original minerals by dissolution and then infilling by precipitation of dissolved minerals in water, or by sulphur-respiring bacteria that form pyrite in place of the original mineral.

It's been a while since I learned all of this so anyone who is up-to-date, feel free to correct me.

IANAP, but the way I heard it explained is that a black hole bends space-time so much that a straight line curves back into itself as a circle. Thus light fails to escape not because it lacks enough speed, but because there is no straight line it can follow that exits the black hole.

Theoretically, maybe? The biggest problem with that is that you can't physically get faster than that, even theoretically

To reach a speed faster than light relativity needs to be wrong. Asking what relativity predicts in situations where it doesn't apply is meaningless. You could ask the question in a completely different framework, e.g. in Newtonian physics (where motion faster than light is possible), but then you don't have black holes any more so you run into the same problem of the question having no answer.

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Its not really due to a speed requirement, but the curvature of spacetime. Black holes bend spacetime so much that any path sort of wraps around back to the singularity.

Our current understanding would technically allow something that goes faster than the speed of light to get out of the event horizon, as that exists due to the speed of light. However a lot of things will be broken in physics if such an object exists and we don't think they do.

No. The geometry of black holes is curved that every direction leads to the singularity. Unless that speed was ∞, no.

1: I think its better to say that the population explosion and climate change are both a result of the industrial revolution.

2: No. Populations dont have some innate ideal size that nature regulates for. But of course no population can grow forever, it will always be limited by some resource eventually. But there is nothing that ensures a population will collapse after reaching a limit, although it does happen sometimes.

\1. No, we know the the green revolution happened and there was lots more stable food, so population grew.

Climate change is due to increased use of fossil fuels. There are parts of the world that have low density population / high fuel use, such as the United States. Opposite, there are parts of the world with high population density / low fuel use, such as any poor country you can name. Overall: statement is both incorrect and too simple.

Why did the green revolution happen? Going deeper, higher population means local areas start to run out of available renewable fuels (e.g. you chop down your forest faster than it can grow.) The industrial revolution was mostly a search for more fuels. Then someone works out how to turn natural gas into fertilizer and all of a sudden anyone can grow more crops in a given area. More people = more fuel = more food = more people.

I am pretty sure the gravity of the expanded star overcomes the outward pressure caused by the fusion reaction and thus it collapses into a dwarf star that is heavily compressed. So no, it won't stabilise, but during and after its expansion, there would be new Goldilocks zones.

The rate at which the sun's luminosity will change will vary at different parts of the process, but it would never really be as stable as it is now. The habitable zone has some "width" so some of the outer planets might remain in it for something like hundreds of millions of years (depending on how exactly you define it), but nothing like the billions Earth has had.

In principle, yes. In practice that mirror would need absurd dimensions, and a black hole doesn't get sufficient light back to even see the Sun.

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Apparently it was junk they ejected. It will enter the atmosphere soon to burn up.

Historians and archaeologists work hard to make sure their dating methods are as accurate as possible.

A relatively simple way scientists date things is by using carbon dating. Now, this is only accurate a few hundred years either side, due to the nature of carbon dating. However, by any more than ~200 years is not really going to happen. We just have too much evidence.

The stonework has been proven to be actually pretty easy with the simple tools they built, it just took a lot of slaves to build it.

And it's unlikely, just due to the sheer amount of evidence we have, from a fossil record if you mean that much older, to built structures, or lack thereof.

Gas giants with a breathable atmosphere would look different from our current gas giants, but you can wear an oxygen mask. Wind would be a concern. Radiation is okay if you get sufficient shielding from the atmosphere. Temperature is a problem unless you are pretty deep in the atmosphere or have a good suit. Saturn's "surface" gravity is just a few percent larger than Earth's, that should be fine. On Jupiter you have 2.5 g however, that is a big problem.

It does. Any finitely-sized region of the universe today shrinks toward zero volume as you approach the Big Bang, but the universe as a whole can still be large, even infinitely so, at the moment of the Big Bang.

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For the thrust part : yes, the artificial gravity created in the ship would just be the floor pushing you towards the ship's up. This is why the designs of spaceships with artificial gravity all have a rotating part usually around the axis of the ship. There is a permanent centrifugal acceleration (as long as the rotation exists) in the part that is moving. The artificial gravity would be in this moving part there are some specificities to this type of artificial gravity because of the inertia and momentum in circular motion. There is a great Tom Scott video on this subject I'll try to find it.

For your biology question re gravity. There are actually a lot of interesting studies on this using the International Space Station. Sometimes when astronauts return to Earth they cannot stand at all due to their muscles degrading as they become disused. For bones I would think that without as much gravity they would be able to grow longer resulting in taller people. Indeed, when astronauts return from the ISS they are taller than when they left as their spine is less compressed.

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Both these possibilities are well explored in the Expanse series of books (and TV shows).

If a ship is always under thrust, people inside will experience the equivalent of gravity. Humans need gravity (as evidenced by issues of returning astronauts).

If you had a VERY efficient fuel source, you could remain under thrust throughout your journey except at the mid point where the ship must flip (i.e. accelerate at 1.0 g for half the trip and then decelerate for the second half and so have almost constant gravity). This uses a LOT of fuel though so is not practical with any known propulsion system.

Expanding is "a thing space can do" according to general relativity, but there is no corresponding theoretical explanation for how or why objects would shrink. It's also not clear how objects shrinking would reproduce observations like Hubble's law - why would objects further from us be shrinking faster?

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There is no "outside the universe" by definition.

Since your question assumes the multiverse existed, then the big bang in such a case was the universe borrowing some energy from the interuniversal distances. Now,this energy would be internuniversal, so there was no energy escaping.

The German chemical company Brabag was able to successfully make oil from coal in WW2 on the scale of a factory. Downside is it cost about 4x as much as simply extracting oil and refining it. Doesn't sound like much, but you could build 4 refineries for the price of that single one. Only makes sense when your nation has so much coal it's almost free and you are isolated from oil producing countries.

Then it depends on how close we need it to look to crude oil and what you need it to do.

To make a forgery to pass some legal case could be done, but it would be expensive to the price of maybe $10k - you would probably take an existing oil and add a few extra things to it.

To make a synthetic oil for lubrication is easy. We can even turn biomaterial into synthetic oils.

However, all of this is usually negated by the cost to be practical. You end up in silly situations where you have to burn half your oil to make the next batch.

There is a process to create jet fuel using the energy from a nuclear reactor and sea water (basically driving the burning reaction backwards) that has been developed for use by aircraft carriers. http://large.stanford.edu/courses/2012/ph240/klopfer1/

In simple terms "oil" is just a mix of hydrocarbons, all of which are easily synthesized in a lab but the energy required must come from somewhere.

Yes, this most famously happens in nuclear reactors where emitted electrons move through the water at speeds greater than light does. This creates the blue glow you might be familiar with through cherenkov radiation, a phenomenon analogous to a sonic boom.

Yes but the thing is we don't know the limit precisely. Eventually, as you add more and more protons and neutrons together, they stop being bound together. This is known as a Proton or Neutron dip. Idk how much 500 protons would even be like but it'd have a very very small lifetime. Micro if not nano or picoseconds.

According to one recent paper the Earth's core might have stopped moving relative to the surface, which is to say it's still rotating as fast as the surface is. From an outside perspective, essentially the core is going from rotating slightly faster than the surface to slightly slower. Per the paper, this happens pretty regularly and won't do much.

If the star is massive enough, wait, or add more material to increase its fusion rate so you have to wait less.

If the star is not massive enough, add more material and then see above. For most stars that means you'll have to multiply their mass by a factor 10-100 or so. At this point, do you still make the original star have a supernova? Or do you just throw the original star into a larger star which ends up in a supernova soon?

Depends. There's lots of reasons it shouldn't work yet it isn't forbidden by relativity. The main problem with it is that it requires negative pressure and we have no idea if it even exists. Negative pressure= negative energy=negative mass. Literally, -1 kg.

And even then, we would only be able to contract and expand spacetime to a finite extent before we run into the fact that it would require more negative pressure than the energy in the observable universe. That's impossible.

When we mean ‘falling’ we talk of being captured in a gravitational well and being forced to move around it if the body is rotating. And you can fall in accordance as long as you share a barycenter. So yes, we are technically falling in the Local Group's gravitational well.

>If everything is falling does the expansion of space mean there’s always room for everything to continuously fall?

Eh..... roughly yes.

Classical physics cannot describe quantum physics- but quantum physics can replicate classical. The main reason we don't use quantum physics in the classical realm is because it's far too mathematically challenging for large systems.

This Q&A might be helpful for a better understanding.

No. The math doesn't work out the same. You can use Classical Physics to explain things like Feynman Diagrams and you can't use QM to explain the universe at a large scale.

That's only their perspective. To us they move but to their perspective, distance doesn't exist at all as the time they were created and the time they were emitted are the same time. It's just a consequence of Relativity.

It's not quite right to say that "time stops at the speed of light." It's better to say "time becomes undefined at the speed of light." But what's interesting is, so does length due to length contraction. So using layman's terms, you could say time stops, but also, it doesn't have to go anywhere, because lengths are all zero.

Dark matter was originally theorized to explain discrepancies between scientific predictions and measurements. But it turns out, it has predictive power. When we estimate the amount of dark matter we think there must be in the universe, it actually explains the relative amounts of Hydrogen and Helium we see in the universe now.

The same amount of dark matter, with the same basic properties, can explain galaxy rotation curves, galaxy cluster dynamics, large scale structure, the CMB anisotropies, and the primordial abundances of chemical elements.

"Something is wrong with the measurements" has none of that predictive power, and even more quantitative ways of stating that (e.g. modified Newtonian dynamics) cannot explain the data as well as dark matter does.

No, the answer to the first question is "there's no reason to think those numbers should match". Asking the question in the first place requires some kind of misunderstanding about the big bang and/or observable universe, but it can be hard to pin down exactly what that misunderstanding is.

But if a question actually included the words "expands at the speed of light", it would be easy to identify that misconception, because that's not at all how expansion works. It doesn't have a speed. It's like increasing the scale factor of the universe, everything getting further apart from everything else, and a uniform dilation preserves distance ratios between things, which means the recession velocity of an object must increase with distance. Two objects can be expanding away from each other at any speed you want as long as they are far enough apart.

The distance at which things expand away from us faster than C is around 14.5 billion lightyears (the hubble radius). So the objects in the observable universe that are further than that have been expanding away from us faster than C ever since they passed that distance.

The observable universe is defined as containing everything we could have ever observed, not things that we could still receive a signal from if emitted "right now" in cosmic time. That is once again the hubble volume, which is just a sphere with r = the hubble radius.

> If QED says light travels in the path that minimizes the time of travel

It doesn't say that. Classical optics says that if diffraction is negligible.

> shouldn't all the light from an object become part of the mirage image in situations involving mirages?

No. Why would it?

> (I.e., why would there be a "real" image as well since that light takes longer to arrive at the observer.)

The direct image will take less time, but it's on a completely different path so that comparison doesn't matter. The shortest path statement only applies to adjacent paths.

Which model do you mean?

Orbital parameters in our Solar System change by more than 1 millimeter all the time and it doesn't matter at all. You could move any planet by thousands of kilometers and no one would care (besides the confusion how the thing suddenly went to a different place).

Time dilation applies to everything, doesn't matter if you use an atomic clock or a pregnancy to measure x months.

As seen by the ship nothing changes because the ship is at rest relative to the ship and only relative velocities matter.

Before calculus you probably took a class where you did lines (slope/intercept form, etc), right? Think about all the word problems where you wanted to know the slope of the line- when you wanted to know "rate of change" or "how much more it costs to build one more object" or anything like that. All of those types of problems require calculus if you want to do them for anything more complicated than a line.

As an example- perhaps you had a problem like this:

> A car is traveling down a race track in a straight line. At t=10 seconds it's 100 meters down the track, and at t = 20 seconds it's 150 meters down the track, how fast is it traveling? Where did it start on the track?"

So, you find the slope and intercept of the equation, and say "oh, it's traveling at 5 m/s, and it started 50 m down the track.

But if the car isn't traveling at a constant velocity, instead you say "at t = 0 seconds a car starts from rest and is 100 m down the track. At t = 10 seconds, he's 200 meters down the track, and he was accelerating the entire time. How fast is it traveling 2 seconds after it starts to accelerate?" well now you need to use calculus. You need to find the slope of the tangent line to the equation that describes his position. You hear physics terms a lot because in general, velocity is the derivative of position, and acceleration is the derivative of velocity (aka- the tangent line to the position graph is the velocity, and the tangent line to the velocity graph is the acceleration, just like the slope of a line in a linear graph is the velocity).

Obviously nonsense.

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