Score
Title
97
AskScience Panel of Scientists XVIII
553
AskScience AMA Series: I am Melinda Krahenbuhl and I am the director of the Reed Research Reactor, the only nuclear reactor operated primarily by undergraduate students. AMA!
10109
What elements are at genuine risk of running out and what are the implications of them running out?
278
Can you break sound barrier under water or any other material?
4029
What’s the largest star system in number of planets?
9
Does knowledge have mass? If so, how much does it weigh?
4
Does smoking THC extract or plant-based marijuana have long-term effects on memory?
5
We can see galaxies and some other objects that are millions or even billions of light years away, some of them might not exist anymore. How can we know or estimate if a star or a galaxy still exists?
18
Why does plastic turn white at the creases when folded/bent?
6
Are people taking immunosuppressant drugs, for example transplant recipients, less susceptible to autoimmune diseases?
3
How does radiation poisoning work?
6
When throwing stuff, does our brain actually try to calculate how hard it has to throw for the item to land at the desired point? Or does it just estimate based on experience?
5
How does thermal imaging work?
3
Could we make an artificial cell?
21
Do microwaves leave residual changes to molecules after heating?
3
Does the temperature have any (noticable) effect on air resistance?
3
What makes a given smell/taste "bad" or "good". Why do we interpret them one way or the other?
0
How do matches work? (The matches that generate fire obviously)
1
What happens to the jaw after permanent teeth grow in?
2
How is the height of the mountain measured?
0
How does mold grow inside ice machines?
4
Can a setup of hall engines provide enough thrust to keep a satellite stationary above earth?
3
What causes clothes to shrink in the dryer?
0
Is it possible for something underwater to catch on fire?
3
Why do mirages (ie. on a highway or desert) appear as specular reflections when the rough material they reflect off of should only produce diffuse reflections?
1
Why do joints like the wrists and ankles have a whole ton of bones, but joints like the shoulders only have two?
9
How does a memristor work?
3
When I move my phone left to right in a dark room while looking at this image, the text appears to jiggle back and forth like jello, or almost like a parallax. Why?
5
Do other species, animals, etc. experience the placebo effect?
2
What are the neurological or psychological differences between the auditory hallucinations of voices, e.g., as in schizophrenia, and a persistent negative internal monologue in one's own inner voice?
3
How do you measure the effectiveness of vaccines without a controlled experiment?
1
What makes the felid species "Neofelis" so distinct from others and a member of Pantherinae?
3831
What is the effect, positive or negative, of receiving multiple immunizations at the same time; such as when the military goes through "shot lines" to receive all deployment related vaccines?
1
Why did the “the Black Plague” and similar plague like events occur, some with massive impact, and why did they end?
2
I've read that when Betelgeuse explodes, it will create high levels of light at night for several days, but would a supernova on the "day side" of Earth even be visible at all?
2
Does listening to music or videos through headphones/earphones affect actual hearing after extended periods of use?
1
By what cycle do potholes develop?
4
If a planet had a radius that was equal to the altitude of Earth’s geosynchronous orbit, but had the same mass and rotational period as the Earth now, would there be reduced or zero gravity on the surface?
1
Does sound travel slower the deeper you are in water?
1
What is lost and what is preserved in a particle collider?
8
Why does snow melt in the sunlight, even when the temperature outside is below freezing?
14
Mar's summer temperature can be 20 celsius. Could a human survive with just an oxygen mask?
4 stuck_in_box_world The reality is electrons have a probabilistic nature, which is born of their wave-like nature. There is no transitory period between energy level transitions. Your case about multiple electrons decaying simultaneously to the same spot is interesting. Your best resource is the Pauli exclusion principle, where two electrons have can't occupy the same state and spin. But the idea that one transition interrupts the other by "beating it " in a race to the lower energy level is looking too far into things because in an X Ray tube K and L transitions are happening all the time and their intensities are based on probability but with a VERY high sample size. So I don't think that this event, if it exists, would make any significant affect on a characteristic spectrum. Understanding wavefunctions may help eliminate your concern over this. Hope this was helpful. I'm a graduate student studying this stuff but am in no way an expert haha
5 xenneract Answering the title question, electronic transitions do take time on the order of hundreds of attoseconds (a billionth of a billionth of a second). These are the kinds of things that [can be measured with pulsed X-Ray lasers](https://phys.org/news/2014-12-attosecond-laser-movie-fast-electrons.html). For most physical and chemical purposes, this is as good as instantaneous.
6 My-Revised-Identity This question is ripe with classicalities so it's best to indirectly answer the question by explaining how we talk about QM. First: we do not talk about trajectories in QM. Saying the particle had a trajectory that would allow us to describe a transition being interrupted is intractable in the language of QM. We have a couple of analogous concepts such as time uncertainty and lifetime of the transition but these are distinct from the duration of the transition. Second: if two distinct but identical particles were to 'compete' to decay into one lower state we cannot talk about which particle actually did decay. The two particle excited state is a superposition state where both particles have probability to be in either state but we cannot know which is which, there is no way to label them. More exactly, any label we apply to the system gives us an observable that would disturb the system and invalidate what we were attempting to measure in the first place. For the issue of the X-ray tube I think you are concerned about a cascaded decay. This can happen in a few ways in atomic systems. For a cascaded decay the electron decays to a lower unstable or metastable state then again to (likely) the ground state. This will produce two photons that will likely be of different wavelengths and hence distinguishable in a fine grained measurements. And potentially a measurable time delay depending on the lifetime of the intermediate state. In other systems, particularly crystals such as KTP and BBO you can have nonlinear optical effects but the one we're interested in here is uniquely quantum and that's Spontaneous Parametric Down conversion or SPDC. Here you send in a laser of frequency 2f and get out two identical (and possibly entangled) photons each of frequency f to some uncertainty. Of course none of the last two paragraphs matter because your second point doesn't conserve energy but it should give you perspective. Those decay paths produce photons of different energies and are distinguishable so you don't have to worry about interference assuming you measure the photons energies.
5 0 stuck_in_box_world The reality is electrons have a probabilistic nature, which is born of their wave-like nature. There is no transitory period between energy level transitions. Your case about multiple electrons decaying simultaneously to the same spot is interesting. Your best resource is the Pauli exclusion principle, where two electrons have can't occupy the same state and spin. But the idea that one transition interrupts the other by "beating it " in a race to the lower energy level is looking too far into things because in an X Ray tube K and L transitions are happening all the time and their intensities are based on probability but with a VERY high sample size. So I don't think that this event, if it exists, would make any significant affect on a characteristic spectrum. Understanding wavefunctions may help eliminate your concern over this. Hope this was helpful. I'm a graduate student studying this stuff but am in no way an expert haha
5 0 xenneract Answering the title question, electronic transitions do take time on the order of hundreds of attoseconds (a billionth of a billionth of a second). These are the kinds of things that [can be measured with pulsed X-Ray lasers](https://phys.org/news/2014-12-attosecond-laser-movie-fast-electrons.html). For most physical and chemical purposes, this is as good as instantaneous.
7 0 My-Revised-Identity This question is ripe with classicalities so it's best to indirectly answer the question by explaining how we talk about QM. First: we do not talk about trajectories in QM. Saying the particle had a trajectory that would allow us to describe a transition being interrupted is intractable in the language of QM. We have a couple of analogous concepts such as time uncertainty and lifetime of the transition but these are distinct from the duration of the transition. Second: if two distinct but identical particles were to 'compete' to decay into one lower state we cannot talk about which particle actually did decay. The two particle excited state is a superposition state where both particles have probability to be in either state but we cannot know which is which, there is no way to label them. More exactly, any label we apply to the system gives us an observable that would disturb the system and invalidate what we were attempting to measure in the first place. For the issue of the X-ray tube I think you are concerned about a cascaded decay. This can happen in a few ways in atomic systems. For a cascaded decay the electron decays to a lower unstable or metastable state then again to (likely) the ground state. This will produce two photons that will likely be of different wavelengths and hence distinguishable in a fine grained measurements. And potentially a measurable time delay depending on the lifetime of the intermediate state. In other systems, particularly crystals such as KTP and BBO you can have nonlinear optical effects but the one we're interested in here is uniquely quantum and that's Spontaneous Parametric Down conversion or SPDC. Here you send in a laser of frequency 2f and get out two identical (and possibly entangled) photons each of frequency f to some uncertainty. Of course none of the last two paragraphs matter because your second point doesn't conserve energy but it should give you perspective. Those decay paths produce photons of different energies and are distinguishable so you don't have to worry about interference assuming you measure the photons energies.