Disclaimer: I’m not a physicist, but I am a scientist. Science as a whole is usually taught in school as though we already know everything there is to know. That’s not really accurate.
Science is really sort of a black box system. We know that if you do this particular thing at this particular time, then we get this particular response. Why does that response happen? Nobody really knows. There’s a lot of “vague” or unknown things in all of science, physics included. And to be clear, that’s not invalidating science. Most of the time, just knowing that we’ll get a consistent response is enough for us to build cool technologies.
One of the strangest things I’ve heard about in physics is the quantum eraser experiment, and as far as I’m aware, to this day nobody really knows why it happens. PBS Spacetime did a cool video on it: youtu.be/8ORLN_KwAgs?si=XqjFEjDfmnZX31Mn
If you repeat the setup/performance, does it stop again? If it was plugged into the mains like your keyboard, A transient voltage anomaly might be to blame?
The keyboard stops recording after 4 minutes. So now, the trickier part is to explain the correlation between the keyboard and the phone. The abrupt stop of the keyboard’s recorder affects, in a yet inexplicable way, the phone’s camera.
Studies of gene flow are probably more what you’re looking for, rather than phenotype. I’m 10 minutes from heading out the door so I don’t have time go hunting for links, but if you search for information about haplogroups, molecular clocks, and mitochondrial DNA you’ll be able to find a lot of information about the history of gene flow in humans.
That is absolutely correct. The atmosphere is held in place, so to speak, by gravity. It is also spinning along with the earth. Some of the atmosphere is lost to outer space at a regular rate and again replenished by natural processes that are beyond the scope of your question.
What’s more interesting is the atmosphere is pressurized at a decreasing gradient the closer it gets to outer space thereby relinquishing the idea that a container is necessary to house all of our atmosphere. (I watch a lot of flat earth videos for funzies.)
I think someone urgently needs to come up with one of these solutions:
The foot-operated lid;
The toilet with flush and suction;
The Jedi throne (a Jedi-style toilet lid activated by hand movements) and lastly
The Terminator (a time-activated flames of hell) solution. The time-activated mechanism locks the toilet door after the user leaves and burns the entire compartment at solar flare temperatures.
Jim’s a clever guy. We could even seek inspiration in some trash cans that have embraced the pedal idea. Can you believe we’re in the 21st century, surround by ai systems, risking extinction for various reasons, and unable to solve the toilet seat conundrum?
In France they have public toilets that basically do number 4. The toilet gets completely cleaned automatically with hot water and detergent after you used it. It works by locking up after you unlocked the door after using it. If you hold the door for someone, they get the cleaning treatment.
Unfortunately, I’ve never been to France, but nothing beats a spotless clean public toilet. And, thanks for the tip: if someone holds the door for you, kindly step back. That alone should be highlighted in all tourist guides.
It’s written quite clearly on the door, but last time I used one I saved a tourist who would have had an unfortunate shower. She grabbed the door when I went out and was going in, I had to warn her and tell her to first let the door close so that the wash cycle would do its job.
You know what they say: you have to rush when Mother Nature calls. Under those circumstances, it can be difficult to read the instructions first. Good to know you saved the poor tourist a free chemical bath.
At that point in Earth’s history, the atmosphere was a lot more oxygen rich than it is now! This allowed all sorts of creatures to grow to immense sizes, like trees, insects and dinosaurs. Dinos like Brontosaurus probably grew large for the same reasons Giraffes did too. The best greenery is the one no one else can get to!
grew large for the same reasons Giraffes did too. The best greenery is the one no one else can get to!
Recent evidence in the fossil record regarding giraffids suggests their necks did not evolve to be long for feeding purposes, but rather sexual selection / fighting for dominance with their necks and heads.
Not sure you got the oxygen part right. But I can say that since trees and animal breath each others exhaust, they won’t both thrive due to atmospheric oxygen concentration.
Observation cannot travel faster than the speed of light. No matter what it is you’re using to observe: Photons (light and radiation), measuring gravity, heat, anything. No matter if the phenomenon’s expansion were traveling at the speed of light, the changes to the universe being made as well as our ability to observe them are also traveling at the speed of light.
If the phenomenon were very far away, we would not be able to observe anything it was causing until its leading edge caught up to us. Then we would be destroyed at exactly the same time. This is because in your example it is expanding at exactly the same rate as the universal speed-of-light constraint allows us to receive any indication of its presence. Any evidence of, e.g. a far away star being destroyed would take X amount of time to reach us by its light no longer arriving. However, in that time the edge of the space-destroying phenomenon will also hit us, because it will also take exactly X amount of time to reach us, at the speed of light, from the point where the star was when it was destroyed. The distance is the same, the speed is the same. We would continue to receive light from that star in the meantime, as we already do. (The light from the stars you see in the sky now is already tens/hundreds/thousands/millions/etc. years old depending on the distance to the star in question.)
If the phenomenon were so far away that it is outside of our observable field of the universe, it will never reach us and we will never have any indication of its presence. That’s what “observable universe” means. Anything can happen anywhere outside of the observable universe and it is objectively meaningless to us, because we will never ever be able to reach it, record it, have it influence us in any way. This is, however, predicated on the theory of the perpetually expanding universe being true (which it probably is).
If you want to actually see the stars in your sky winking out over the millennia, I suggest building your universal destruction bomb such that its shockwave travels at, say, half the speed of light or some other suitable fraction.
Thanks, I was having trouble intuitively on that tipping point of expansion moving objects faster than the speed of light and how that is observed without more than lunch napkin level thought. Makes sense. We would never know about or see “the bubble” if it stopped short due to expansion.
The best we can achieve in this thought experiment is to see through a telescope some faraway alien set up a bomb with a countdown timer that will surely blow up at a specific time in the future and destroy the universe, but which we’ll never see count down to zero or explode. If we saw it reach zero it would of course kill us in the same instant as we see it, because by the rules of the thought experiment the explosion travels at the speed of light. But if the alien is far away and the countdown is long enough, the accelerating expansion of the universe due to dark energy will carry it outside of our cosmic event horizon before it explodes.
Using the cosmic comoving distance definition and the cosmology calculator, the last scattering surface of the Cosmic Microwave Background for example is 45.5 GLy away. Its light was emitted 13.7 GY ago (400kY after the Big Bang) at redshift 1100z. I was told that due to accelerating expansion, we will never see galaxies further than 63 GLy away (we don’t see them yet, the matter that we’ll see form them is beyond the CMB sphere for us at present), and if we hopped onto a lightspeed spaceship right now, we can never reach galaxies beyond 17 GLy comoving distance.
So for example if we looked at a galaxy at redshift 3z which is 21 GLy away, and whose light took 11.5 GY to reach us, and saw the alien set up the bomb timer to 11.49 GY, we know that the bomb must have surely exploded by now, but also know that we are safe because it’s far enough away and we’ll never see it explode, even in the infinite future.
Similarly, we can relish the tiny shred of joy in the knowledge that if we did fuck up something really major, like creating a false vacuum bubble in the LHC or whatever, we can never destroy more of the universe than the 17 GLy bubble around us.
An explosion wouldn’t change the gravity situation though. Gravitational waves are not relevant here. The danger of an explosion would be the physical matter stripping the atmosphere, and radiation. I think it would take quite a bit longer before Earths gravity is affected significantly based on the drag from traveling through the debris. A gravity well is about the total mass in the center. So wouldn’t a significant amount of material need to make it past the orbit of earth before the orbit is directly altered? The expansion would impact the rotation of matter from the stellar body, but that is not coupled to an orbiting body in a vacuum.
You are right! People often say “what if the sun blew up” in the context of gravity speed vs. light speed thought experiments, but what they really mean is shorthand for what if the entire sun was somehow deleted in a single instant with no trace. But in reality, “blowing up” the sun is much different than “deleting” it and leaves its entire mass behind, just spread around more.
There is even a theorem in general relativity that proves that massenergy cannot be deleted, invalidating a whole swath of such thought experiments. Forgot what it’s called though.
“I suppose the surprising thing is why the atmosphere doesn’t all fall immediately to the Earth’s surface to form a thin dense layer of air molecules.
The reason this doesn’t happen is that air molecules are all whizzing around at surprisingly high speeds - typically hundreds of metres per second depending on the temperature.
The air molecules bash into each other and knock each other around, and the air molecules near the ground bash into the air molecules above them and stop them falling down.”
If it were zero then all the air would indeed just fall down to the ground (actually, this is a simplification I’ll address later).
As you increase the temperature the atoms of the ground will start to wiggle more and they’ll start to kick the air molecules giving them non-zero average height.
So the atmosphere would move a little off the ground. The bigger the temperature is the higher the atmosphere will reach.
Note: there are number of assumptions above that simplify the picture. They are not that important but I want to provide a complete picture:
1, Even at the zero temperature the molecules would wiggle a little because of quantum mechanics
2, The atmosphere would freeze at some point (like 50K) so under that temperature it would just lie on the ground
3, I assumed that the ground and the atmosphere have the same temperature because they are in the thermal equilibrium; in reality their temperatures can differ a little because of additional slow heat-transfer processes.”
This is the way! It helps me to imagine what would it look like if the atmosphere consisted of a single nitrogen molecule. You place it on the ground but the ground has temperature (is warm) so your one molecule gets launched up into the vacuum on a parabolic trajectory at 500 m/son average. If it launched at 45° it would reach 6km up and fall down, at 90° - 12km up - and that’s on average. Some would get launched faster and higher (following the long tail of the Boltzmann distribution), and hydrogen and helium even faster still because they are lighter. A few hydrogen molecules would be launched at speed above 11km/s, which is above Earth’s escape velocity, so they would escape and never fall down.
When you have many air molecules, they hit each other on the way up (and down), but because their collisions must be perfectly elastic, mathematically it works out that the overall velocities are preserved. So when your one nitrogen molecule gets launched up but on its way hits another identical molecule, you can think of them equivalently as passing through each other without colliding at all. (Yes, mathematically they can also scatter in some other random directions, but the important part is that your original molecule is equally likely to be boosted further upwards as opposed to impeded.)
The end result is that majority of the atmosphere stays below 12km, density goes down as you go up though never quite reaching zero, and hydrogen and helium continuously escape to space to the point none are left.
It does, but as more air drops down, the pressure increases. This pressure then starts to push back against the air above it. Which is why we have atmospheric pressure at the surface, but that goes down to pretty much 0 in space.
Even in low earth orbit there are still some particles, which causes satellites and such to slow down, requiring them to fire some thrusters every once in a while.
So, I’m not a virologist, so I can’t answer about viruses. But I am a bacterial microbiologist, so I can talk a bit about pathogenic bacteria. Short answer: yes. Long answer: yes, kind of.
It really depends on what the vaccine is targeting and what the pathogen is. My favorite pathogen is Streptococcus pneumoniae, the leading cause of pneumonia. So let’s look at it from that perspective. There are vaccines for S. pneumo, but the vaccines only target certain stains of S. pneumo. And every 5 or so years, we make a new version of the vaccine because the types of S. pneumo that are causing disease keeps shifting. If the vaccine accounts for type A, then type B starts to cause more disease. If the vaccine accounts for types A and B, then type C starts to cause more disease. If the vaccine amounts for types A through C, then type D starts to cause more disease. Repeat ad nauseum.
So yes, we can cause shifts in pathogen populations through vaccines. This is evolution, in its strictest definition. That being said, there’s a lot of caveats. First, that doesn’t mean that vaccines are bad. Maybe we want to shift the population (for instance, toward a milder form of the disease). Or maybe it doesn’t strictly matter if the shift occurs (if we can just keep making new vaccine versions, a la S. pneumo).
Second, even though vaccines may be shifting the population, that doesn’t mean that it doesn’t work. The S. pneumo vaccine significantly decreased infection and mortality from pneumonia. And while a lot of people still die from pneumonia today, it’s nothing compared to the mortality before modern medical science.
Third, it really depends on the vaccine. Specifically, how hard is it for the pathogen to mutate that portion that the vaccine is attempting to mimic? There are certain proteins that are more difficult to mutate than others. For instance, there are certain proteins that are involved in binding to and attacking the host. These proteins tend to be somewhat difficult to mutate, since mutating those proteins tend to also make the pathogen less efficient at attacking the host. If the vaccine trains the immune system to recognize these proteins, it can be really difficult for pathogens to evolve away from these proteins. Not to say that it’s impossible for pathogens to evolve anyways (pathogens are surprisingly tricky), but a well-designed vaccine, along with good adoption in the population, can significantly hinder a disease.
Reading between the lines, my bet is that it is looking for photos with less atmospheric blurring. Since it sets reference points, it can measure the delta from a good shot, add the values to detainee how close to ideal a particular photo is, then choose the overall “luckiest” photos and stack them.
I read that article, and it’s very good! But it didn’t explain how detect atmospheric blurring, since it’s not actually blurring, it’s distortion. To quote that article
even if the sharpest image is very clear, it may still be distorted in varying degrees around the frame So you can’t just score the frames by sharpness.
Assuming all images are compared to a reference shot as you suggested, how is the reference shot selected?
I’ve actually got my own ideas about how it could be done, but this is coming from a background in computer science, not from astronomy, so I don’t trust my solution.
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