Does anyone have a list of long-term effects that may arise from periods of severe dehydration in childhood, particularly how this might affect overall health in adulthood?

"Stronger" hearts typically have a resting pump rate lower than that of weaker or less healthy ones. A healthy, athletic male might have a resting BPM of 60, while an otherwise healthy but post-partem female could be closer to 90.

Would both of these hearts expend the same energy pumping 120 BPM? Would the healthier heart be theoretically expending more as it is acting in double-time, or would the weaker one be working harder as it is already inefficient at pumping blood?

Seems like it should and the result should be one. Does mathematics agree with me on that?

As in, are there some parts of physics that aren't as clear-cut as they usually are? If so, what are they?

I know it can be a hot topic. I have long wondered what the real isolation timelines were for East Asia, India, Africa, and Europe. I'm most curious about the first two as they seem so divergent. Like a group had to be mobile enough to relocate, but then stay within a region for a (?) long time with little influx.

It is a shame that this seems to be such a loaded topic. Hopefully I have framed the question with something of a social filter. I am not interested in the sociopolitical or pseudo science nonsense.

I understand how lucky imaging gets the results it gets, but I'm wondering specifically how the 10% of frames are chosen.

They're not picked based on clarity/blur, because the problem is one of distorted images not blurry images, causing issues when averaging the stack.

Searching online gives me lots of answers about how lucky imaging produces clearer images, but not how the lucky frames are chosen.

Anyone know how lucky frames get chosen?

I mean, why evolution selected dinosaurs to become that huge?

More of a classification question, but I'm really curious about what the metric would look like if we try to be systematic about it.

For context, there's several countries that are more or less famous for being geographically discontinuous. Top of the mind nowadays is Azerbaijan, whose sizeable territory of Nakhchivan has no land connections with the rest of the country. There's also Equatorial Guinea, whose capital city is on island which is smaller than the continental territory. That's the same for Denmark, although we seem to think of it less, because of the much smaller distances and significantly more connectivity. Then you have Indonesia which I currently think might be the most discontinuous country, with territory spanning across at least 4 major landmasses but which are shared with other countries.

But then you have countries such as Greece, Japan, or even Sweden, which are more or less archipelagic countries but do not stand out in the way Indonesia or Azerbaijan does.

How can we define a measure of geographic discontinuity that gives us a reasonable ranking? I would imagine we start with some measure that looks how much of the whole territory is in one contagious unit (less prominent main landmass = more discontinuity) but perhaps we also introduce average distance between units.

Just a thought, if an event happened well beyond the observable universe that caused entire galaxies to be destroyed radiating from a point source event, what would it look like from our perspective and how close could it get on our observable horizon while still being unable to reach us due to expansion of the universe?

Obviously, the ability to "observe" in this context is extremely relative to the time scale, and far longer than even our species is likely to remain in recognizable form. I want to conjure a mental picture an era where a substantial portion of the distant night sky is a marching black void, and no one is entirely sure if it will halt from expansion or end everything in a flash one day.

Think "you wake up in the woods naked," Dr. Stone-style tech reset. How could humans acquire a 1-gram weight, a centimeter ruler, an HH:MM:SS timekeeping device, etc. starting with natural resources?

My best guess was something involving calibrating a mercury thermometer (after spending years developing glassblowing and finding mercury, lol) using boiling water at sea level to mark 100 ° C and then maybe Fahrenheit's dumb ice ammonium chloride brine to mark -17.7778 ° C, then figuring out how far apart they should be in millimeters on the thermometer (er, somehow). I can already think of several confounding variables with that though, most notably atmospheric pressure.

I feel like the most important thing to get would be a length measurement since you can then get a 1 gram mass from a cubic centimeter of distilled water.

That's as far as I got with this thought experiment before deciding to ask the internet. I actually asked on Reddit a while back but never got any responses.

I am seeking a scientific explanation behind this phenomenon which is unprecedented to me.

I was performing a piece on a music keyboard. I was filming it with my phone's camera as well as recording the sound via the keyboard's built-in tool.

After reviewing the recordings, the film and the keyboard's recording simultaneously stop emitting sound at the same exact millisecond.

This infuriated me quite a lot, but now it intrigues me. What happened there? I am willing ro provide more information if needed.

I was dealing with a problem which stated that two objects were moving with same velocity v and one was a car with mass m and another a truck with mass M, such that M > m. They collided and came to a halt. Their collision lasted for 1 second. Which experienced a greater force of impact?

After searching a little bit everyone seems to have a different equation for force of Impact. What's really force of impact and how is it different from force and Impulse? Thanks!

It is said that ACs are counterproductive in fight against global warming, in that while they may make the local environment temporarily livable, the greenhouse gases produced while making the electricity needed to operate them heat up the rest of the Earth by much more than the relief from the AC itself. By how much exactly is that? Note that here I am interested in the global impact of greenhouse gases specifically, not in the local heat island effect (given how ACs do not destroy heat but only move it from inside to outside, and add extra heat from running the compressor itself). Let's also assume all electricity comes from fossil fuels (ACs might become a viable solution if 100% of AC electricity came from renewable solar, which is actually a reasonable goal to strive for given how both AC and solar are most active during the day, but at the moment most of electricity delivered to me specifically, for example, comes from natural gas.)

Here's my estimate. Let me know if it is reasonable! Methane has energy density of 891 kJ/mol, burnt into CO2 at 1 mol : 1 mol. Gas turbines have efficiency up to 60%. The radiative forcing of CO2 can be calculated as: ln(new ppm/old ppm)/ln(2)*3.7 W/m**2. For example the 131 ppm increase in CO2 since 1750 up to 411 ppm has a radiative forcing of 2.05 W/m**2 (is that across the entire Earth's surface? or only its crosssection?), and CO2 has persistence in atmosphere for at least 1000 years. The atmosphere composition is 78% nitrogen 21% oxygen 0.9% argon so its molar mass is:

.78 * 28 g/mol + .21*32 g/mol + .009*18 g/mol = 28.7 g/mol 

And total atmospheric mass:

4*3.14*(6.37e6 m)**2 * ~10000 kg/m**2 * 1000 g/kg / (28.7 g/mol) = 1.78e20 mol

Suppose 8 billion people each run 1kW AC for 1 year, with electricity from natural gas. (That's similar to our total current global energy consumption of 20TW, though of course we use power for things other than just AC or electricity, but also most energy comes from coal and gasoline not just gas, and 80% comes from fossil fuels not renewables.)

8e9 people * 1000 W/person * 60*60*24*365 s / (891e3 J/mol * 0.6) = 472e12 mol

That's 472 teramols of CO2 (20.8 gigatons) added to the atmosphere each year, or 472e12 / 1.78e20 * 1e6 = 2.65 ppm (parts per million). It is believable that having done so for a hundred years we have raised CO2 concentration from pre-industrial levels up to 411 ppm. The radiative forcing is:

ln((411 ppm + 2.65 ppm)/(411 ppm)) / ln(2) * 3.7 W/m**2 = 0.0343 W/m**2

Or for the whole earth:

4*3.14*(6.37e6 m)**2 * 0.0343 W/m**2 = 17.5 TW

What is my individual contribution for 1 hour?

17.5e12 W / 8e9 / (24*365) = 0.25 W

That is, if I run my 1kW air conditioner for 1 hour, the entire Earth will be solar heated by an extra 0.25 W for the next 1000 years. That doesn't sound like much, but it adds up over time: I spent one kilowatt-hour in one hour on cooling, but the rest of the Earth will be heated by an extra 0.25 W * 24*365 hours = 2.2 kilowatt-hours in the next year, and again every year thereafter. Multiply that by 8 billion people or a hundred years and it adds up a lot, even considering the heat is distributed across entire planet surface not just areas where people live.

So my answer is 1 kWh of cooling = 2.2 kWh of heating per year for the next 1000 years. By same calculation in terms of mass, 1 kg of CO2 = 7.4 kWh of heating for every year thereafter. Is this accurate?

I let people rate how much they like different things on a scale of 1-10. How do I actually tell if people like one thing more than another thing if the sample sizes are different? This is not about any real scientific study, more like a personal test :)

For example, if one thing got voted on 10 times and has an average value of 6.5, and another thing got voted on 6 times and has a 6.1, is the 6.5 thing actually more liked? Or is this small sample size still so random that it could with a high chance go both ways?

I've never done anything like this, if someone could explain it or direct me to the correct key words/links, that would be hugely appreciated :)

I've read up a bit on p-value determination, but I'm not sure what my "null hypothesis" is here actually, numerically. If I'd put it in words I guess my hypothesis would be "this thing is more liked than the other thing", but honestly, it seems like my specific case would be much simpler than all the stuff I'm reading here :D

Feels like a shower thought, but I seriously want to know if there are any implications, because it seems like identical twins are able to sense, understand, and almost be extensions of each other - finish each other's sentences/thoughts. Some even claim to be able to sense their twin when they're separate. Hard to believe, but at all possible?

I am talking about gadgets we see in science fiction movies that obey the laws of physics of our universe and could theoretically be constructed, barring the limitations of materials, energy and time faced by our civilization at the moment.

Does anyone know where I could find a reasonably priced photon pair generator online?

Let's say the quantum uncertainty which is currently quite small and doesn't affect our life on macroscopic scale suddenly increased. Magically we are still living in this weird rule of physics. How would we see daily stuff? like how would I see a ball rolling in my sight?

As the title asks, what is the average mass of each kind of cloud? Ignoring things like overcast days, and only considering clouds large enough to identify. Or maybe rather than "average" it'd be better to say "what is the mass of an archiypical cloud of each type?" Eg an archiypical cumulus, cirrus, cumulonimbus, etc.

There's a good many gravity theories, some that don't even try to explain the why, only the how and other's that involve some particle like the graviton. But anyone know if there's any based on the energetic vibrations of our known particles with mass (those within protons and neutrons)? In other words, gravity's space warp is a result of all the heavy work done by powerful particles; the more mass at work (density), the more space warps.

I found this one, and I recall someone trying to do a current version of it but can't seem to locate it (perhaps being developed outside of English language).

Thanks for any insight.

Where does the sound go to when you’re in a spaceship in space?

The sound hits the hull, and then has nowhere to go, does it get converted into another type of energy?

I know that if an electron collides with its antiparticle, the positron, they annihilate each other and energy is released. But what happens if an electron collides with other antimatter that is not its antiparticle, like an antiproton or an antineutron? Do they annihilate each other too?