Wikipedia:Reference desk/Archives/Science/2016 April 30

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April 30

Can gum chewing remove necessity of ordinary food?

(I will not surely be back)49.135.2.215 (talk) 01:23, 30 April 2016 (UTC)Like sushi

No. Chewing gum instead of eating is like not eating at all (see Sham feeding). Ian.thomson (talk) 01:42, 30 April 2016 (UTC)

Well, gum could be infused with liquid nutrients, which would then be absorbed as you chew the gum. However:

1) You would need to chew a lot of gum (maybe 5 kg/11 lbs ?) a day to get the nutrients you need. Your jaw would get quite tired from that.

2) Some dietary requirements, like fiber, couldn't be delivered that way, so it wouldn't be very healthy.

3) I'm not sure if it would taste very good. Some nutrients, like iron, aren't palatable, so you really want them contained within something you swallow, like a chunk of meat, so you don't taste it. StuRat (talk) 15:51, 30 April 2016 (UTC)

Time Travelling

Will time travelling be really possible in future or is it impossible to happen? — Preceding unsigned comment added by Sahil shrestha (talk • contribs) 04:48, 30 April 2016 (UTC)

Time travel currently is happening in a few ways

• You are currently traveling through time at a rate of 1 second per second.
• All objects moving faster than you are are currently traveling through time slightly faster than that due to time dilation effects as explained through Albert Einstein's Special relativity theory.

Time travel thus can only take you into the future, and how fast you get into the future depends on how fast you are traveling through space (faster moving objects get to the future relatively faster than slower moving objects do).

Time travel into the past is probably impossible, the Grandfather paradox explains some of the problems with why you can't from a lay-person's perspective. Time travel into the past is not expressly forbidden by the various relativity theories (see Closed timelike curve for an explanation), but various physicists have come up with very good reasons why it can't happen, i.e. Novikov self-consistency principle; the main objection to time travel into the past is that it violates Causality. --Jayron32 05:07, 30 April 2016 (UTC)

Great answer!! Thanks Jayron32 — Preceding unsigned comment added by Sahil shrestha (talk • contribs) 05:23, 30 April 2016 (UTC)

Except that Einstein's theory of Special relativity doesn't quite say that. Time dilation based on relative speed is symmetric, and does not depend on some notion of absolute speed. That's the whole point of calling it "relativity". It's true that, according to General relativity, object in a stronger gravitational field will have time slowed, and it's also true that when a "speeding object" decelerates to match the speed of a "stationary" object, it will appear to have aged less, but if the "stationary object" is accelerated to match the speed of the "speeding object", then it is the "stationary object" that will have aged less. Dbfirs 11:51, 30 April 2016 (UTC)

Causality is more religion than science. Though in terms of elegance, I have heard it said that Feynman diagrams include models that seem to violate causality. The harmful effects on free will are as readily encountered by simple precognition as by literal time travel. Wnt (talk) 22:09, 30 April 2016 (UTC)

Whoever said precognition was real? Less thaums required sure but just as impossible (psychics would be cleaning up at the casino) Sagittarian Milky Way (talk) 22:22, 30 April 2016 (UTC)

Well, just as there is only one past, and only one present, there is only one future. And at a zero order of approximation, a person who remembers the future is highly likely to remember losing the lottery. Now there is a deviation from that in that winning the lottery is more memorable than losing it, and a person's actions in the past can influence his odds of winning in the future. A person cannot change the future, but he can be responsible for it. Even so, who remembers what the lottery was yesterday? Remembering the numbers from tomorrow naturally should be more difficult. And such practical uses must compete with far more readily accessible harmful phenomena that tend to shut down the experiment. Wnt (talk) 22:45, 30 April 2016 (UTC)

There is only one future, but it hasn't happened yet. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:07, 1 May 2016 (UTC)

Also see our article Time travel. Loraof (talk) 15:18, 30 April 2016 (UTC)

Nitrogen ice density

What is the density of nitrogen in solid form ("nitrogen ice")? It is expected to be more than 1.0 g/cm³ (see below).

Nitrogen lists 1.251 g/L in gas form and 0.808 g/cm³ in liquid form.

(This is to substantiate the claim "Because water ice is less dense than nitrogen-dominated ice" in Pluto’s Mysterious, Floating Hills. At first, it seems unlikely that an element would shrink 20% or more going from liquid to solid form).

--Mortense (talk) 07:24, 30 April 2016 (UTC)

I found the following sources that agree on a density of 1.026 (or rounded to 1.03) g/cm³ for solid nitrogen:

• This page from Schenectady Community College
• This page at a site called aqua-calc.com
• The book Nitrogen by Heather Hasan, accessed via Google Books.

On the other hand, this paper (written in rather bad English) appears to say that it is 0.85 g/cm³; I have no idea why such widely differing numbers would be found.

--69.159.61.172 (talk) 10:01, 30 April 2016 (UTC)

I have just created the Solid nitrogen page. This also says 0.85 for nitrogen frost. Frost would contain a lot of voids. However at lower temperatures and slightly higher pressure it becomes compact and denser than water ice. For the β higher temperature phase measurements are 0.97, and 1.15 with upto 1.4 under pressure. The α phase - low temperature has density 1.03. But anyway for any of these, water ice is less dense. reference at http://scitation.aip.org/content/aip/journal/jcp/52/12/10.1063/1.1672899 for β phase Graeme Bartlett (talk) 13:51, 30 April 2016 (UTC)

Pluto looks to be warm enough most of the time for the β pahse to be stable. The α phase would only be stable at the coldest times and places. Graeme Bartlett (talk) 13:53, 30 April 2016 (UTC)

Good work! --Mortense (talk) 18:14, 30 April 2016 (UTC)

Quark Flavour Change

In the article Quark, it states

'By absorbing or emitting a W boson, any up-type quark (up, charm, and top quarks) can change into any down-type quark (down, strange, and bottom quarks) and vice versa.'

It then goes on to talk about the chance of a down quark to turn into a top quark, which is 0.009. Despite this small probability, how does a down quark, with a mass of 4.8 MeV turn into a top quark, which according to earlier in the article has a mass of nearly a gold atom, which according to a quick calculation of mine, means its mass is multiplied effectively by over 38000 times. Where does all this mass come from? Thanks, JoshMuirWikipedia (talk) 08:00, 30 April 2016 (UTC)

Well it is not going to happen unless there is a big input of energy from somewhere, eg atom smasher, or Large Hadron Collider. Graeme Bartlett (talk) 13:22, 30 April 2016 (UTC)

The number in the CKM matrix is more like the square root of a probability, but not quite. It is used to compute probability amplitudes. Such probability amplitudes can be calculated with path integrals (other terms occuring in these path integrals will be at least a coupling constant and propagators). The path integral should give you 0 if the energy isn't conserved. Icek~enwiki (talk) 20:39, 30 April 2016 (UTC)

A slight correction: The propagator is rather the result of a certain path integral. When one knows the propagators, one can do "ordinary" integrals over the position of the vertices in Feynman diagrams. Icek~enwiki (talk) 20:44, 30 April 2016 (UTC)

Sector mass spectrometers

Why do sector mass spectrometer analyzers use continuous magnetic fields, instead of pulsed fields? Plasmic Physics (talk) 09:43, 30 April 2016 (UTC)

This question is rather like "Why don't cars have square wheels?" It would increase the complexity of the apparatus, introduce lots of unnecessary transients and mechanical stress, and not have any practical advantages. Tevildo (talk) 17:32, 1 May 2016 (UTC)

Im sure there is a very good answer to this Q. Unfortunately, I have, as yet, been unable to find it by a preliminary search on Google.--178.103.251.111 (talk) 22:19, 1 May 2016 (UTC)

Cars don't have square wheels, because square wheels require a larger torque to turn, hence more powerful engine, and would sure be unnecessarily inefficient. I don't believe that the answer is so clear-cut for my question, I would like to have a more specific answer. I can accept that the complexity of the design would increase, that is a given, however I need reasons for why you say that there are no practical advantages. For one, it seems to me that it is energetically wasteful to use a continuous field. It's not as though the ion stream will recombine after each pulse, or am I wrong. Plasmic Physics (talk) 23:45, 1 May 2016 (UTC)

A pulsed magnetic field would induce electric pulses in every conductor within range, see Faraday's law of induction. The burden of proof lies not in what the OP says they need, but in persuading designers of mass spectrometers that they should change technique and invite new Electromagnetic interference problems where none exist. AllBestFaith (talk) 09:08, 2 May 2016 (UTC)

Is the electric pulses an insurmountable problem, or does it nullify any possible advantage otherwise gained? Certainly the designers are more qualified than me to justify their decision not to use an obvious mode of operation? It would be presumptuous of me to attempt to advise them. Plasmic Physics (talk) 10:53, 2 May 2016 (UTC)

The thing is, it's not an obvious mode of operation. For any measuring instrument, we're interested in accuracy, resolution, and sensitivity. The sensitivity depends mainly on the detector, so we need to minimize the amount of noise and interference it has to deal with - using a static field is one obvious way of doing this. The accuracy and resolution depend more directly on the deflection apparatus, and are improved by keeping the field spatially uniform and of constant intensity; with a pulsed field, we'd need to ensure that each pulse was the same magnitude as the previous one to maintain accuracy, which makes the task even more challenging. Pulsed fields are useful if we need very high intensities that can't be delivered continuously, or if we're interested in the transient behaviour of the system - transients are something we want to avoid in a mass spectrometer, and if field strength is an issue, we can just change the size of the apparatus to give us adequate deflection. Tevildo (talk) 20:40, 2 May 2016 (UTC)

Thank you, that is precisely the type of sensible answer I'm looking for. So, except for the interference and noise, would a very high intensity pulsed field yield greater separation/resolution? Plasmic Physics (talk) 11:03, 3 May 2016 (UTC)

Separation, yes: resolution, not necessarily. To generate the spectrum, we either need to move the detector slit, or vary the field in a controlled manner. With a pulsed field, there will be both variation between pulses and over the length of a pulse, which will make the ion paths less well-defined. We're moving the peaks further apart on the spectrum, but increasing their width, so there's no guarantee that the resolution of the system as a whole will improve. That being said, there might be a situation where (a) physical size is important (otherwise we could just increase the sector size and use a weaker field), and (b) what we want to do is discriminate between two well-defined species with peaks very close together, where using a strong, pulsed field might have advantages. Whether a sector mass spectrometer is the ideal instrument to use in such a situation is another point to consider, though. Tevildo (talk) 21:15, 3 May 2016 (UTC)

The reason that I'm asking, is because I wonder if there is a way to improve calutron design by using modernised technology. Would calutrons be a suitable use for this modification? I'm also considering taking a time of flight approach, by using a switching gate that redirects the second fraction of the ion beam, in this case resolution can be traded with the number of iterations. What do you think? Plasmic Physics (talk) 09:20, 4 May 2016 (UTC)

Yes, the efficiency of a calutron could be dramatically improved with modern technology, but a standard superconducting magnet (as used in an MRI scanner) would be enough; there's no need to go to a pulsed field on top of that. A centrifuge is still a more efficient way of performing the separation, but there are political (as opposed to technological) reasons why it might be unsuitable. [NOTE to the Powers that Be - if North Korea order 200 MRI scanners tomorrow, I would advise further investigation.] Tevildo (talk) 19:08, 4 May 2016 (UTC)

Solar ionising radiation shielding

What atmospheric pressure or density at ground level is required to protect Mars from solar ionizing radiation to the same degree as what Earth is protected from. I am trying to compensate for the lack of a structured magnetic field on Mars. Furthermore, by 'degree' I mean the ratio of incident radiation to ground level radiation. Plasmic Physics (talk) 10:42, 30 April 2016 (UTC)

Don't forget that the composition of the atmosphere will also have a small effect.--Aspro (talk) 11:03, 30 April 2016 (UTC)

Exactly the same as the Earth's atmosphere pressure. Ruslik_Zero 13:36, 30 April 2016 (UTC)

It's further away, too, so the amount of radiation that interacts is reduced by the ratio of the square of the respective radii. I don't think the pressures need to be the same. --DHeyward (talk) 14:45, 30 April 2016 (UTC)

Remember pressure is weight. Pressure doesn't absorb radiation, mass does. Jim.henderson (talk) 15:28, 30 April 2016 (UTC)

True, but for a planet with a given surface area and gravitation field, the more mass of atmosphere you have, the higher the pressure will be at the surface. StuRat (talk) 15:37, 30 April 2016 (UTC)

Note that the thickness of the atmosphere and strength of the magnetic field are not independent. Mars has little atmosphere not only due to it's lower gravity, but also it's weak magnetic field, some 1/40th the strength of Earth's and oddly, confined to the Southern hemisphere. That is, both magnetic poles are in the Southern half of the planet: [1]. Venus, by contrast has a magnetic field about 1/10th of Earth's, but it's more evenly distributed, like Earth's, and can hence protect that planet's atmosphere from being blown away by the solar wind :[2]. StuRat (talk) 15:33, 30 April 2016 (UTC)

• The density of the atmosphere isn't exactly what matters. Harmful UV is screened out by nitrogen, oxygen, and ozone (each affecting different components) -- the densities of those three are what matter. In particular if the atmosphere lacked ozone, no plausible density would give adequate protection -- see ozone layer. Looie496 (talk) 22:01, 30 April 2016 (UTC)

I want to keep the same composition constant. Correct me if I'm wrong, but does exposure of oxygen to UV create ozone in any case, and so a denser/pressurized/massiver atmosphere yields more ozone? Plasmic Physics (talk) 23:20, 30 April 2016 (UTC)

I believe so, but keep in mind that free oxygen in the atmosphere is an unusual thing. We didn't have it on Earth until millions of years of plants giving it off as a waste product allowed it to accumulate. Without plants, that oxygen tends to be all bound to other atoms into different molecules, like bound to hydrogen in water, to carbon in carbon dioxide, to iron in iron oxide (rust), to silicon in silicon dioxide (quartz), etc. StuRat (talk) 23:40, 30 April 2016 (UTC)

OK, so do you or anyone know a best estimation for what would solve my query? Plasmic Physics (talk) 01:42, 1 May 2016 (UTC)

Spring stream in Georgia

A spring stream near Arakhveti, Road E117 / S3 (Georgian Military Highway) (Georgia (country)). Orange colour is caused possibly by iron. What is the nature of the black deposit ?

Etan J. Tal^(talk) 22:16, 30 April 2016 (UTC)

I have seen such orange waters in coal mining country, where black can be finely divided coal. But I don't know it isn't humus or something else just by looking. Wnt (talk) 22:48, 30 April 2016 (UTC)

There are forms of iron which are black, too. Perhaps it's one of those. StuRat (talk) 00:01, 1 May 2016 (UTC)

That looks to me like limestone, but I can't tell whether it has been built up by the stream or cut through by the stream. Looie496 (talk) 00:37, 1 May 2016 (UTC)

Looks like a deposit to me, noting how it's only at the edge of the stream. Further inland, the minerals are tan-colored. StuRat (talk) 00:45, 1 May 2016 (UTC)

Additional information: 1. Gaseous bubbles were seen. 2. The black deposit has asphalt-like consistency. Etan J. Tal^(talk)

Gaseous emissions and black margins to the water-course suggests tufa. The decomposing bio-life turns the associated carbonates black. Place some of the asphalt-like stuff in ordinary vinegar and see if you end up with just black stuff. If so, it is most probably organically derived carbon from plants, bacteria etc. Evaporate some of the water down and you'll then might find this is a spring that contains some carbonates as well. Collect some of the gas from the spring in an upturned jar of water and pass it through lime-water to test for carbon-dioxide. These are some things (that for once) you can try at home. Do not however, try to brew beer from it. It will taste awful due to the high iron content. --Aspro (talk) 21:00, 1 May 2016 (UTC)