Let me recommend the books by Greg Egan. Essentially, he takes some basic premise of our universe’s physics, twists it around, and then writes novels exploring what living in such a world would be like. Superb. You can check his website for an idea, but don’t be scared by it. He drops all the physics and math in there, but the novels shy away from that and use metaphors where absolutely needed.
Someone's already given an answer for a non-illuminated structure, but the necessary brightness of a light to be visible is also an interesting question.
We'll assume the light is located on the dark portion of the Moon. From experience, the dimmest stars clearly visible with the naked eye when right next to the Moon are around magnitude 1, which is about 3.6x10^9 photons/sec/m^2.
If we focus the light on the near hemisphere of the Earth (which has an area of 2.5x10^14 m^2) we need to produce 9x10^23 photons/sec. A green photon has an energy of around 3.7x10^-19 joules, so the total power output is 9x10^23 x 3.7x10^-19 = 333 kW.
For reference, this is roughly comparable to the wattage of the fastest electric car chargers. It's a lot of power, but well within the capability of a small lunar solar farm.
In this case, a very strong eruption ejects kids of super hot gas and rock upwards, like when you open a shaken bottle. After some time, pressure will decrease, and gravity will start dragging things down again.
Unlike a regular soda bottle, heat is significant. Hot gas rises in the atmosphere against gravity. During this rise, it loses energy ( so it cools down). When it reaches a high enough temperature where the lifting momentum is overcome by gravity, it starts falling again.
As the top starts to fall while there still is more material below in the column, the column gets compressed. As the center of the column is the hottest part, it still pushes material upwards. So the colder material falling from the top is pushed outwards, widening the column a bit. It also encounters the cold air outside and starts cooling even more itself, falling ever faster in the outside “ring” of the column. It still is only “cool” compared to the rising inner column, still thousands of degrees. Also, all the light glasses will have moved further up the atmosphere and either fall slower or not at all. This is where the long term effects such as your mentioned ash fall/ rain comes from. So most of the rapidly falling material that then form pyroclastic flows are actually fairly heavy liquids/solids and heavier-than-air gasses. They only seem so light and fast inside a pyroclastic flow because if their immense temperature and contained energy.
However, sooner or later the falling material encounters the ground, a solid obstacle. As the inner column is densely filled with super hot, probably still rising fresh material, the only possible way is outwards. And with continuous pressure from above from all the falling material, the material needs to move out of the way very rapidly. This is not dissimilar from how water behaves that flows from a bottle or faucet and hits solid ground. But a pyroclastic flow is a bit more viscous, and still very hot. While moving outwards, it quickly has to push away the cool, resting atmosphere. The only way for the air is to step aside upwards. Now, as the cold air likes to stay close to the ground and was compressed, it forms a seemingly paradoxical barrier layer of cold, dense air above the pyroclastic flow, pressing down on it, even squeezing it further outwards. This together with it’s own viscosity means there’s surprisingly little turbulence between the two layers, with the hot flow continuing to rush along below the cold barrier layer instead of mixing and rising through it upwards. If this interests you, look up inversion layers: they are a normal phenomenon in regular weather as well, especially winter time, and can sometimes even last many days.
Consider that ash columns reach many km in altitude, filled with many tons of material. It doesn’t all fall slowly at the same time. It’s literally rock falling from high atmosphere to the ground, carried by heavier-than-air gasses that also want to sit below the atmosphere.
yes you can do this, however notice: this is wasteful as you have to run pump and heat from steam condensing is not recovered. You can heat up incoming water with condensing steam - this is called vapour recompression distillation. alternatively you can use heat pump to move heat around
When we breath, we use the oxygen, but we do not use the nitrogen. The nitrogen can actually be replaced with another inert gas and the “air” is breathable. Thinking about diving specifically, nitrox is actually an oxygen rich (nitrogen poor) mixture. More extreme mixtures use helium in place of some nitrogen (and sometime oxygen depending on the depth).
In your body, the amount of oxygen in our blood is critical for survival. Having a lot of nitrogen is actually not good. Too much is what causes the “bends”, again related to diving.
When looking at exoplanet atmospheres, we look for oxygen rich because it likely indicates water. We believe that planets with a high amount of water are more likely to support life similar to ours. It is possible that another form of life exists that doesn’t need oxygen or water, but we know for certain that oxygen and water can support life.
I think its like peppers, they’re all the same specie but we’ve bred strains for different purposes, so you’ve got the whole range from bell peppers, to habaneroa, to shishitos.
It might work, I know there’s types of beer based on wild yeasts, but it probably takes special care and is going to take more effort to get the flavor your want from it.
I just learned about this whole God forsaken idea from this post, and it’s disgusting. However, one thing I know for certain is that the type of people who would buy vaginal yeast brewed beer(typing that almost made me gag) ain’t buying it for how it tastes.
Close enough I graduated last year 2023. I couldn’t get in to the college I wanted so I decided to try it a second time. There’s a countrywide exam that gives you a score. It’s called yks. I’m currently studying for that exam.
Rounding of constants always depends on what you are calculating. Getting a rocket into orbit is a case to use the actual local value of g with a bunch of digits (and the change with height, too). If you build a precision tool, some more digits of PI are no bad idea.
But to calculate the lenght of fence to buy to surround a round pond, I actually used 10/3 for “PI plus safety margin” once.
It depends on whether the light is within a medium or just in vacuum. Afaik light in vacuum behaves entirely linear (so waves of different frequencies don’t interact). But there are materials where light does indeed interact with light of different frequencies. One effect like this is so-called four-wave mixing. https://en.wikipedia.org/wiki/Four-wave_mixing?wprov=sfla1
In general you can take a look at non linear optics
I will! Thank you! Also, it’s super fun that there’s exceptions based on the medium; I had no idea. I was picturing air or vacuum when I conceived of the original question, so now I have other things to look into!
I second the other poster’s suggestion to look into nonlinear optics. A really common application is frequency doubling, also known as second harmonic generation, which doubles the energy of the photons. So an 800 nm laser (red) can be converted to 400 nm (green) with this method.
Another optics-based phenomenon that I think maybe strays too far from the intent of your initial question, but is too cool not to share, is laser Wakefield acceleration. A very high power laser pulse will push electrons out of its path in plasma or materials via the ponderomotive force. This charge separation creates electric field gradients on the order of billions of volts per centimeter, which can accelerate electrons or other charged particles to relativistic energies. So you can start with a green laser pulse and wind up producing gamma-ray beams, either by slamming the electrons into a stopping material or by Compton scattering other low energy photons off the relativistic electrons.
I really appreciate the extra info! It’s fascinating.
I’m recently an ex-fundie, so learning about all the cool stuff happening in science is like finding out your childhood house has a million secret rooms you never knew about.
No, because frequency is a fundamental quality of a wave. Things that are affected by one frequency could also be affected by another in certain cases (such as when two frequencies are integer multiples), but the waves themselves will never affect each other.
As an analogy, imagine playing a specific note on a flute. It doesn’t matter how many other notes you play, that original note will always be there alongside the others.
Thanks for the analogy! It’s pretty easy to understand how that works. I think I was imagining that EM waves shared some qualities with mechanical waves like sound, but I suppose that’s not the case!
well i’d say that trees grow in both ways: the stem grows on the outside because it’s acting more like our bones, but the bark acts like our skin and indeed grows in the same way, new matter being created at the base and pushed outwards, hence why a lot of bark has tons of cracks in them from the stretching.
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