Wikipedia:Reference desk/Archives/Science/2019 June 7

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June 7

Breakthrough Starshot Query

An extract from your article on Breakthrough Starshot reads; The Starshot concept envisions launching a "mothership" carrying about a thousand tiny spacecraft (on the scale of centimeters) to a high-altitude Earth orbit and then deploying them. A phased array of ground-based lasers would then focus a light beam on the crafts' sails to accelerate them one by one to the target speed within 10 minutes, with an average acceleration on the order of 100 km/s² (10,000 ɡ).

Many scientific minds have been involved in the development of this idea, but I just can't understand how a ground-based laser could remain in the ideal position for 10 minutes to accelerate one of these "Star chips" exactly towards a galaxy 4.37 light years away. Surely the rotation of the earth would move the laser "sideways" off target in a matter of seconds? Any enlightenment on this would be most welcome! 49.197.104.112 (talk) 06:32, 7 June 2019 (UTC)

I confess not understanding it all, but the problem you envision seems no problem to me. Taking care of the rotation of the earth is one of the job of a telescope mount. Gem fr (talk) 06:47, 7 June 2019 (UTC)

In science fiction everything is easy ;). But yes you'd steer the beams to compensate for the earth's rotation and also for atmospheric turbulence. Or you could bypass the latter problem by putting the lasers in space or on the moon. 100GW though? And getting that gossamer sail to survive 10,000g of acceleration? Good luck with that ;). 173.228.123.207 (talk) 06:53, 7 June 2019 (UTC)

(OP) Thanks, but keeping the beams pointing at the Starchips as the Earth rotates doesn't accelerate them towards their target49.197.104.112 (talk) 07:34, 7 June 2019 (UTC)

Laser propulsion is the article explaining how a laser could give the desired acceleration (see also: solar sail) Gem fr (talk) 08:07, 7 June 2019 (UTC)

Enough light to accelerate something at 10,000 g, sustained for 10 minutes? I don't think I appreciated the scale of the project. That is a big honkin' space gun. Also the sail, to avoid being vaporized, must reflect the light nearly perfectly, which I think means that if you make it flat enough, that is a big honkin' space gun that could be reflected and aimed back at targets on Earth. I think I begin to see the reason for the idea's popularity. Wnt (talk) 09:04, 7 June 2019 (UTC)

considering the mass m of the thing to be accelerated (cm size -> gram mass; pretty much the same as a bullet) we are talking of force=a/m of a ten to hundred Newton magnitude, and power=F.v 100.60,000,000 ~ 1-10 GW range. (unless I made some mistake). So, yes, this is the magnitude of laser weapons currently developed. Gem fr (talk) 19:58, 7 June 2019 (UTC)

Breakthrough Starshot is the article in question. Could the angle of the sails be adjusted to compensate for the slight change in the angle of the incoming laser beam ? But either a laser in Earth orbit or on the Moon would seem to make more sense. Both have the advantage of no atmosphere to deal with, while Earth orbit has the advantage of being easiest to reach, with the right orbit being able to eliminate the Earth's rotation as an issue. The Moon has about 1/28th the Earth's rotation, but has the advantage of slight gravity, making working on the laser simpler (no tools and screws and astronauts floating away), and you don't have to worry about orbital station-keeping, and sensitive equipment (power source, spare parts, etc.) can be placed underground to protect it from gamma rays, etc. If this laser is to be a long-term investment, then the Moon may be a better option, especially if a nuclear reactor is to power it all, which we really wouldn't want in Earth orbit. That way, the nuclear waste could just be left on the Moon. SinisterLefty (talk) 12:12, 7 June 2019 (UTC)

The whole point of the system is to have the power source on earth, so you don't need to put it on orbit Gem fr (talk) 19:58, 7 June 2019 (UTC)

Dealing with the atmosphere alone seems to make this impractical. SinisterLefty (talk) 20:01, 7 June 2019 (UTC)

Surely atmosphere is a problem, but current telescope technology seems to have solved most of the issues by using proper location and ... lasers. Gem fr (talk) 08:49, 8 June 2019 (UTC)

Adaptive optics can somewhat reduce the problem, but not solve it entirely. Otherwise, there wouldn't be any point in space telescopes like Hubble. And if the cost was less, we would presumably have far more space telescopes. But, in the future, we can predict that the cost of space launches will come down, now that we are starting to see the commercialization of space launches, with SpaceX and such. SinisterLefty (talk) 22:49, 8 June 2019 (UTC)

for the point of a space telescope, see Hubble_Space_Telescope#Successors. Many reasons wont apply to a laser, and you have to consider the problem of the huge power source Gem fr (talk) 23:07, 8 June 2019 (UTC)

If we were talking about making this today, then yes, a much larger Earth-based laser would make sense. But as the rest of the technology for this project seems decades away, when the cost of space launches will be far lower, that logic will no longer apply. I can also predict a time when Earth-based telescopes will be considered obsolete, except for hobbyists, with serious science all using space-based or Moon-based telescopes. Manufacture of the mirrors, lenses, etc., in space would also eliminate any distortions introduced by gravity. SinisterLefty (talk) 03:39, 9 June 2019 (UTC)

(OP) Would a laser of that power output have an "opposite and equal reaction" ?? ie if you put it at a Lagrange point, would the reaction from the power output force it back in the opposite direction? Also I think that a sail restrained only around the edges could never stay flat enough under that incoming power to reflect a coherent beam back to earth.49.197.104.112 (talk) 00:09, 8 June 2019 (UTC)

Yes on the equal and opposite reaction, but if the laser unit has a mass a billion times that of the target, it would only be subject to a billionth the acceleration of the target, assuming 100% efficiency. Still, some orbital station-keeping would eventually be required, hence the advantage of placing it on the Moon. The L1, L2, and L3 Lagrange points are stable in one direction (towards the line connecting the Earth and Sun), so will tend to fall back towards that line, but are unstable in the other direction, towards or away from the Sun and Earth. So, if you could arrange it so the push was in the right direction, it's possible that the laser unit might find a way back to the Lagrange point by itself. But this turning out to be the push direction you want would require quite a coincidence. SinisterLefty (talk) 08:35, 8 June 2019 (UTC)

Unruh effect - simulation or confirmation?

Any commentary on [1] would be welcome. Our article on Unruh effect says it "may" have been observed in 2017; this article says it hasn't been, but now it's been simulated in a Bose-Einstein condensate with magnets. Are the magnets accelerating the atoms or not? The coherence means it's quantum, what does that mean? Etc. Wnt (talk) 14:29, 7 June 2019 (UTC)

This is, of course, a simulation, not a confirmation. Ruslik_Zero 15:54, 7 June 2019 (UTC)

Alright, let's go to [2]. It says "By modulating the magnetic field at frequency ω near a Feshbach resonance, a jet-like two-dimensional emission of atoms with momentum k_f = √mω/h observed few milliseconds after the modulation, where m is the atomic mass. Such emission forms a fluctuating bosonic field, also called “Bose fireworks”, and is a result of bosonic stimulation." That sounds sort of like real acceleration to me, which is one of the many reasons why I'm confused. Wnt (talk) 18:51, 7 June 2019 (UTC)

Vocal range in human (speech, not singing)

What is the (realistic) vocal range in women for ordinary speech? I understand there are some very rare exceptions, but what is more or less reasonable to assume?

I came across the claim in the Elizabeth Holmes article: ″During most of her public appearances, she spoke in an unusually deep baritone voice, although a former Theranos colleague later revealed that her natural voice was actually a few octaves higher.[15]″ - Is it realistic that a woman has a vocal (speech) range containing a few octaves and still sound more or less natural in her low- (baritone) and her high-pitched speech? I've only found the articles on vocal range and voice classification in non-classical music so far, which seem to be restricted to singing. Am I overlooking a more relevant article? --Ibn Battuta (talk) 22:05, 7 June 2019 (UTC)

The article is nonsense so far as evidence goes. Even if we take a low value for 'a few' as 2 then the difference of 2 octaves uses up a signficant pert of your range. I could maybe believe half an octave. Greglocock (talk) 22:27, 7 June 2019 (UTC)

The article editor(s) should try to find some clips of Tallulah Bankhead. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:51, 8 June 2019 (UTC)

I've heard some high-pitched women speakers who I think routinely speak in an upper register that I thought til just now was falsetto, but the falsetto article says the actual falsetto mechanism is different from what I thought. Anyway that register can easily be an octave or more above the lower part of the modal register. The vocal fry article has an interesting paragraph:

Some evidence exists of vocal fry becoming more common in the speech of young female speakers of American English in the early 21st century,[4][5][6][7][8] but its frequency's extent and significance are disputed.[9][10] Researcher Ikuko Patricia Yuasa suggests that the tendency is a product of young women trying to infuse their speech with gravitas by means of reaching for the male register and found that "college-age Americans [...] perceive female creaky voice as hesitant, nonaggressive, and informal but also educated, urban-oriented, and upwardly mobile."[4]

So maybe that's what Holmes was doing. 173.228.123.207 (talk) 08:21, 8 June 2019 (UTC)

• Well, the link would be Falsetto#Use_in_speech, but the article does not look in great shape.

Basically, the articles about singing apply, since one can speak at any pitch that one can comfortably sing, as long as one is used to it. I would imagine EH decided that speaking with a lower pitch would project gravitas and was worth training.

Assuming [3] is a representative excerpt, she does not use vocal fry. It is probably the lower end of her modal range (still much higher than a baritone voice in terms of frequency even if the voice "sounds" similar). My OR from practicing classical singing (which, in addition to being OR, is likely to be a biaised sample since it covers trained singers) is that almost all men (90%+?) speak at pitches very close to the lower end of their tessitura (a couple of tones above it at most), but there is more variation in women (maybe because of the easier falsetto transition?). Tigraan^{Click here to contact me} 08:06, 10 June 2019 (UTC)

It is a fact that after the birth of their first child the pitch of some women's voices goes down. 2A02:C7F:A42:AD00:6D9E:CD5D:662E:5310 (talk) 17:09, 14 June 2019 (UTC)

Audio anplifier

How much louder is a 300w amp than a 100w amp?. And why do amp manufacturers emphasise the wattage above anything else? 86.8.201.182 (talk) 22:49, 7 June 2019 (UTC)

I mean, could I detect the difference,? 86.8.201.182 (talk) 22:51, 7 June 2019 (UTC)

About 4 or 5dB. Depends a lot on the definition of "Watt" and how relatively honest each manufacturer is. Also a larger amplifier into the same speakers will be less effective (electrical power to loudness tends to be more efficient at lower levels for the same speaker).

3 dB is a doubling of power, and is considered to be the increment that's easily discernible to the listener. So yes, you'll hear it.

Watts are easier to measure. They're also an attribute of the amplifier alone, not the amplifier and speaker combination. Andy Dingley (talk) 22:57, 7 June 2019 (UTC)

Also, if the speakers can't handle 300 watts, there would be some rather noticeable distortion and possibly blown speakers. SinisterLefty (talk) 23:42, 7 June 2019 (UTC)