Almost always yes, but there can be exceptions.

For a bright source the level of detail you can see using an optical instrument is limited by whichever is "worse" of two factors. Firstly, the inherent resolution of the instrument because light is a wave and it diffracts around edges. A perfect point light source produces a blurred image at the focal plane, known as the Airy disc. For a telescope the resolution depends on the diameter of the main mirror/lens (the aperture) and the wavelength. (I don't know for microscopes).

Secondly, the visual acuity of the eye multiplied by the magnification in use.

In general when using "low" magnification for a given instrument the second factor is the limit, while with "high" or "too much" magnification the first factor becomes the limit.

2x is low magnification for almost anything, but if you had a telescope with an exceptionally small objective lens it could be limited by diffraction.

This doesn't seem right, not in all cases anyway.

In most clinical trials the patient knows that it's a clinical trial, what condition is being treated, and that they will be randomly given either the treatment or a placebo. It would be unethical for the participants to not know that.

You seem to be thinking of psychology studies, where it is commonplace to tell subjects and workers a study is about one thing when really it's about another.

This is known as orbit determination.

https://en.wikipedia.org/wiki/Orbit_determination

A telescope can observe what direction something is in, but cannot directly measure the distance. But because an object's motion depends on its distance from other masses (mainly the sun), three observations at different times are sufficient to determine the orbit. Newton worked that out for the special case of a parabolic trajectory and later scientists refined the mathematics and extended it to all orbits.

The observations have error bars, which means the orbit determination also has error bars. Observations over a short period of time tend to result in less precise orbital information than observations spaced further apart, and extra observations are good to have. (And in some cases, we actually have radar distance measurements.) The error bars on the orbital information mean that a prediction of the future position of the comet is less precise the further into the future it is, and if the comet will pass a planet close that amplifies the errors. For small bodies like comets and asteroids non-gravitational effects, mainly relating to solar radiation, can perturb the orbit and they are hard to predict. All these factors mean don't usually know for certain that an asteroid or comet will hit or miss Earth, but instead you read things like a "1 in 100 chance of impact in 20xx".

Even if you completely covered every other part of the body, if you look at the sky, about 20% of the thermal radiation from your eyeballs escapes into space.

The Local Group is what's known as a galaxy group, with a few dozen galaxies, in contrast to larger galaxy clusters with hundreds or thousands of galaxies. So yes, it's sparse compared to the giant clusters, but not exceptionally sparse. The more massive clusters are much rarer than the small groups.

https://www.mpe.mpg.de/2040034/clusters_and_groups_of_galaxies

What seem particularly rare are isolated "void galaxies", but there are a few known. https://esahubble.org/images/potw1545a/

There are a few plants in the Antarctic Peninsula, yes https://en.wikipedia.org/wiki/Antarctica#Biodiversity

But as far as we know, there was never a long-lasting human presence on Antarctica until industrial times. There still has never been an economically self-supporting settlement on the Antarctic mainland, only bases reliant on continue funding to operate.

The world's climate was a bit warmer in the last interglacial about 115,000 years ago, but there's no evidence for humans doing any long ocean voyages back then. Sailing long distances over the open ocean is difficult and the pattern of human migration was to spread over the continents. Most of the Pacific islands, with much more favourable climate than Antarctica, were only settled by humans within the last 2000 years.

You don’t need a prism. A directional light source produces a recoil force. For a near-perfect beam like a laser you need 300 megawatts per Newton.

Acute radiation sickness. Specifically from neutron radiation. Even that is in a sense indirect - the neutrons knock nuclei about or get captured by the nuclear forces, but it's secondary emission of ionising radiation that does the real damage and that's electromagnetically.

Yes, by conservation of momentum if light is refracted in a way that's not symmetric, momentum must be imparted to the lens. It doesn't even need to be a single pulse - a prism will refract light asymmetrically, and an off-axis section of a spherical-surfaced lens will do it.

The “atmosphere” of the moon is a surface boundary exosphere. This means molecules are ejected from the surface (by various processes), fly on a ballistic arc, then hit the surface again with almost no chance of encountering another molecule on the way.

Without interaction between molecules, the atmosphere does not behave as a fluid and cannot form winds.

Any object with enough gravity that ejected molecules have a decent chance of falling back, but no denser atmosphere, will form a surface boundary exosphere.

This might be the case for some electric cookers but not all.

I ran a short experiment on mine. A Beko model D 532, solid plate electric hob. Power consumption was measured with a home smart meter. Each time the ring was set to a given power setting, the power consumption reported by the meter changed within a few seconds then stayed stable over the course of a minute with variations of only +/- 10W at most. The maximum power measured of 1950 W reasonably agrees with the manual which lists a max 2000 for that ring.

Any "bang-bang" control would have to switch on and off on a timescale of seconds or shorter while making no audible noise.

Without disassembling the cooker I cannot say how the control is done, but how it could be done is with multiple heating coils within the solid plate and only some are used at lower power settings. The control "clicks" between numbers with in-between setting not possible, which would be expected with such a control method.

The oven, on the other hand, has a continuously adjustable control. It uses bang-bang control with a thermostat, which is a common approach for thermostatically-controlled heaters. The oven is aiming to maintain a certain air temperature, by contrast the hob settings are for a certain heat output.

Full numbers. All rounded to 10 W with errors of about +/- 10 W.

0: 300 W (Edit: This is the consumption of the other electrical appliances in the house, so needs subtracting from the other figures to get the power used by just the cooker. I checked during the middle of testing and again at the end and it remained consistent.)

1: 500 W

2: 540 W

3: 610 W

4: 1150 W

5: 1440 W

6: 2250 W

I don’t know any specific term. A lake like you describe is a rare thing. They might occur in karst terrain, but the size of any such lakes are fairly small. The largest cenotes (flooded sinkholes) are a few hundred metres across and won’t necessarily have a below the waterline undercut.

I agree with other answers that puncturing the balloon and letting the payload fall to a lower altitude for capture would be the way to go. I don't think it would be reliable though because the balloon does not have a designed grab point like various re-entering space capsules have had.

That said, the Lockheed U-2 is still in service and has a service ceiling of 80,000 feet or more. There are some high-altitude drones that get into the 70,000 feet range, such as the Airbus Zephyy. Although I don't know what such an aircraft could actually do about a balloon. Trailing a grappling hook seems a bit too Looney Tunes to work.

Ice has less thermal energy than water at the same temperature, which more than offsets the slight increase in gravitational potential energy due to ice Ih (the stable form at STP) being less dense.

On a molecular level, when the water molecules have slowed enough with cooling they can form permanent (ish) hydrogen bonds with each other and the shape of the molecules creates the ice crystal structure, even though this means pushing the molecules apart a bit more.

The University of British Columbia uses a long distance pneumatic tube. The video doesn't mention Technetium, but they use it for C-11 with a half life of 20 minutes.

https://www.youtube.com/watch?v=eMTZvA8iFgI

That's unusual; road transport is more common. The production, from a particle accelerator, is quite common for certain isotopes though.

All materials have structural limits. A column, made of a certain material in a certain gravitational field, will either crush or buckle under its own weight if it is too high. This still applies if the gravitational field is the self-gravity of the structure itself.

Dynamic support might be used. One concept is you make a sort of long skinny particle accelerator and the particles going back and forth exert a reaction force on the endpoints supporting the far end. But even with that, the bottom end loop has to be able to support the load.

Based on known materials, even a solid Dyson sphere is impossible without dynamic support. A realistic Dyson sphere would instead be simply a swarm of satellites so dense it can absorb nearly all its star's light.

The ultimate limit is that the volume of a region of space scales with radius cubed, but the critical mass above which a black hole is formed scales linearly with radius. Thus the larger a structure is, the less dense it must be to stay below that critical mass. (Which in any case could only be approached by transporting matter in from other galaxies, since the starting galaxy was obviously not a black hole.)

Once you're at the point that the "structure" is a thin mesh of wires or tubes stretching over interstellar distances, well, why have the structure at all instead of just a bunch of free-floating spacecraft that can share power and data with lasers or something?

Spectroscopy.

The surface temperature can be determined by the relative intensity of different spectral lines (the letter and number in the spectral class) or by the colour index (bluer is hotter).

If the distance is known independently, then given the apparent magnitude, distance, and surface temperature, the radius can be determined.

The width of the absorption lines in the star's spectrum (the Roman numberals in the spectral class) allows to infer the surface gravity of a star. And if you know the radius and the surface gravity you can calculate the mass.

https://en.wikipedia.org/wiki/Stellar_classification

I don't know about the microscale. There is variation in muscle tissue, such as "fast twitch" vs "slow twitch" fibres, but I don't know of any studies correlating (or not) such variation with sex.

Men on average have more muscle mass and lower body fat percentage. As well as that there is a difference in muscle distribution. Compared to women, men have a significant advantage in upper body strength but a more modest advantage in lower body strength. I've seen varying figures from different sources but the difference clearly exists. Upper body strength is important for punching, throwing objects, and wielding weapons - all abilities required to fight and to hunt.

Even if they're the same height and weight and have the same skill and general fitness, that upper body strength gives the man an advantage in a fight, which is likely to be one reason why combat sports usually separate men and women in competition even though they also have weight classes.

> Evolutionary Design: Men are built to hunt and protect, while woman play the major role in reproduction and care taking of the next generation.

I don't think this stands up to scrutiny. Firstly the idea that hunting was a male activity in forager societies has been called into question by archeological evidence such as https://www.science.org/doi/10.1126/sciadv.abd0310

Secondly, the same sexual dimorphism exists in the other Hominidae (great apes) to a varying extent, with no correlation to how much hunting the species does. In particular gorillas do virtually no hunting but have males much larger than females. An evolutionary explanation for sexual dimorphism that's applicable to all great apes is simpler than appealing to a different explanation for each species.

I agree with other answers that fighting is a more probable driver of sexual dimorphism in great apes than hunting. If, in human forager societies, more hunting was done by men this could be as much the result as the cause of the sexual dimorphism.

In classical mechanics, if the stiffness (ie the relevant elastic moduli for the wave type) tends to infinity or the density tends to zero then the speed of sound tends to infinity. Am I correct to think that when you apply special relativity, the speed of sound would tend to c and not infinity in those limits?

Iron can fuse but the fusion absorbs energy instead of releasing it. So it only accelerates the collapse of the core.

You can get similar reactions with chlorine, fluorine, and some compounds of them such chlorine triflouride. Indeed ClF3 will combust with oxides such as sand and asbestos.

You can get combustion with various oxygen-containing compounds too, such as nitrous oxide.

The late fusion stages in a high mass star, say 25 solar masses, are brief indeed. The overall life of such a star is only about 3 million years, but in the dying stages:

Carbon burning - 600 years.

Neon burning - 1 year.

Oxygen burning - 6 months.

Silicon burning - 1 day (!).

And then the iron core collapses, in most cases triggering a supernova. (Some ranges of stellar mass and metallicity result in collapse to black hole without a supernova.)

http://abyss.uoregon.edu/~js/ast122/lectures/lec18.html

The Doppler shift in the frequency from a satellite transceiver is measurable and needs to be taken into account. In ham radio use this means adjusting the frequency on the ground transceiver during the satellite pass. Commercial systems will automate such corrections.

https://n1aae.com/visualizing-satellite-doppler-shift/

https://upcommons.upc.edu/handle/2117/123510

What will help is something in the signal that the receiver can "lock on" to in order to tolerate slight mistuning. With analogue modulation that's a "carrier" frequency which has no data but provides a frequency reference the receiver can "lock on" to. AM, FM, and analogue TV include such a carrier. By contrast single sideband with no carrier, popular in ham radio, will give the receiver an audible pitch shift if they are not precisely tuned. For digital modulation things are more complicated but there are still ways to handle that mistune, and indeed devices don't give the user control over the precise frequency.

https://en.wikipedia.org/wiki/Carrier_wave

Yes.

https://ntrs.nasa.gov/api/citations/19730006364/downloads/19730006364.pdf

Page 178. Reports a tolerance of 16 g with immersion in water.

https://www.esa.int/gsp/ACT/doc/BNG/ACT-RPR-BNG-2007-09-SuperAstronaut-IAC.pdf

Page 8. Mentions 24 g.

The limit is from the air filled lungs. Studies in mice show triple the g tolerance and for a much longer time period if the lungs are emptied of air. I believe they hooked the mice up to a heart lung machine; doing that for humans purely to achieve higher g tolerance would almost surely not be considered worth the risk.

Liquid breathing is discussed in the second paper I linked but I don't think it has been demonstrated in active humans. It's been used for medical treatment but that's in the context of stuff like inducing therapeutic hypothermia. Anyway the liquid used is much denser than water so that's a problem for the g tolerance idea.