Wikipedia:Reference desk/Archives/Science/2015 May 14

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May 14

The nature of empty space

In the latest issue of Astronomy magazine (June 2015) on page 30 there is an article with the above title. On page 33 the author expands into the issue of vacuum energy. I think the piece is poorly written and this is why I am here. In the section "The power of nothing" he mentions the Casimir effect: "...Casimir showed that closely spaced metal plates become powerfully (!) pressed together, presumably by the waves of vacuum energy outside them." And this is the major point: "Calculations of how much vacuum energy lurks everywhere vary greatly (in fact, the 100 orders of magnitude difference between theoretical predictions and measured values is known as vacuum catastrophe), but it is substantial. By the larger estimate, if this energy could be extracted and utilized, each empty mayonnaise jar of space contains enough power to boil off the Pacific Ocean in one second." My questions:

1. According to the author, what is larger: experimental or theoretical estimate by 100 orders of magnitude?
2. How is experimental vacuum energy measured?
3. Why is the vacuum energy measured by the volume?
4. Energy, vacuum or not, is in fact mass. So, one can collect some hypothetical mass into a mayonnaise jar and blow up the Pacific Ocean?
5. What do you think about the paragraph above?

Thanks, - --AboutFace 22 (talk) 02:03, 14 May 2015 (UTC)

Just to correct one thing for you as a misconception in your thinking. Mass (and energy) is not a substance. It is a property of a substance. You cannot collect "mass" in a jar anymore than you can collect blue in a jar or collect sour in a jar or collect temperature in a jar. Properties of objects are not substances unto themselves. They are properties. Mass is not stuff. Matter is stuff, but mass/energy is but one property of that stuff. --Jayron32 02:30, 14 May 2015 (UTC)

• First, theoretical calculations of the vacuum energy usually assume an approximation to a black-body spectrum, which would be a huge amount of energy compared even to the calculations of dark energy based on observation. Second, vacuum energy is relative to volume, since vacuum is spatial by definition. Third, the problem with black-body estimations is that the energy would indeed be enough to equal mass at the E=mc^2 conversion rate to stop and reverse the expansion of the universe. Instead, this expansion is apparently accelerating. This is my lay understanding as a bachelor in biology with about 35 years of reading on the subject, so don't take what I have implied as worth more than the links I have provided. Finally, "what do you think about the paragraph above" is not a question we answer here, see the page guidelines at the top on opinion and debate.

μηδείς (talk) 03:26, 14 May 2015 (UTC)

We have an article on the Casimir effect. It's a QED problem similar to how black holes can radiate due to virtual particles formed at the event horizon. Metal plates separated by a vacuum but very close together can interfere with the creation of virtual particles creating forces that otherwise would not be there. --DHeyward (talk) 06:16, 14 May 2015 (UTC)

Well, the usual explanation of the Casimir effect is basically bunk; it's not wrong as such, but you can explain anything in QED that way. See hep-th/0503158 (which is linked in the article, but not nearly as prominently as it should be). -- BenRG (talk) 10:33, 14 May 2015 (UTC)

A very crude estimate of the energy needed to boil the Pacific Ocean is 710,000,000 km³ × 1 g/cm³ × 1 cal/g°C × 100°C ≈ 3×10²⁶ J = 300 YJ. To boil it in one second you'd need a power of 300 YW. This is suspiciously close to the total output of the Sun, so I wonder if the author got his examples confused. Applied to the vacuum energy, it's way off: the naive theoretical prediction according to this page is around 10⁹⁶ kg/m³, or 10¹¹⁰ joules per liter, so a 500 ml mayonnaise jar of it would boil 10⁸³ Pacific oceans. (But you can't really do that; it just shows how wrong the theoretical prediction is.) -- BenRG (talk) 10:33, 14 May 2015 (UTC)

Thanks for the answers which convinced me that there is still a rather sketchy understanding what the vacuum energy is. Of course I cannot delve in Quantum Chromodynamics to understand it. Still I want to know: How is the vacuum energy measured experimentally? --AboutFace 22 (talk) 17:18, 16 May 2015 (UTC)

The height of Everest

I don't see this in our article and searching for this is difficult considering the terms. Did the height of Everest change after the recent earthquake in Nepal? Dismas|^(talk) 03:53, 14 May 2015 (UTC)

It's mentioned in Mount Everest#2015 avalanches. DMacks (talk) 04:31, 14 May 2015 (UTC)

Everest lost an inch in height due to plate shift.[1] μηδείς (talk) 00:40, 15 May 2015 (UTC)

There has been a major aftershock closer to Everest since that measurement. Rmhermen (talk) 06:13, 15 May 2015 (UTC)

Yes, but such pre-and aftershocks are NOT countershocks. Else they would so be noted in the press. μηδείς (talk) 07:03, 15 May 2015 (UTC)

Thanks, DMacks! Dismas|^(talk) 00:48, 16 May 2015 (UTC)

Resolved

Relative regularity of clocks?

These are two naive questions I am sure have been answered many times so bear with me. By a clock I simply mean a device that measures time.

1. How would you determine experimentally that one clock is more regular than another, i.e. that the phenomenon on which one is based is more strictly periodic that the other? It seems to me it can't be done. As far as I can tell you'd just have to assume your chosen fundamental clock is the most regular you can get, and work out your physics going from there, using the well known back and forth between observation/experiment and prediction. But is that correct?

2. Let's assume I am correct about the first question. Now suppose you take two clocks and build two alternate physics using those two clocks. Will a more regular clock lead you to a simpler (or less complicated) physics than a less regular clock?

Thank you for any answer.

Contact Basemetal here 13:47, 14 May 2015 (UTC)

For 1. you choose a physical phenomena which is known to occur on a strictly regular pattern. For example, a Crystal oscillator uses a form of piezoelectric oscillation to act as a timing regulator. You could also use other forms of harmonic oscillation, including things like tuning forks or pendulum (which is how old-timey clocks did it) or even light waves (which is how the official second is defined). --Jayron32 14:16, 14 May 2015 (UTC)

But how do you know it occurs on a strictly regular pattern? It seems to me you'd already need to have a physical theory to tell you that, and to construct that physical theory you'd already have to have a way to measure time. Looks to me like a vicious circle. Contact Basemetal here 14:57, 14 May 2015 (UTC)

I believe Huygens, Newton, Hook et al. would use their pulses as a crude form of time measurement. But once you get the idea that the motion of a pendulum might be regular, you don't need clock to perform the analysis that says that the period of an idealized pendulum is constant. See pendulum_(mathematics), and simple harmonic motion. This was known to Huygens (and is also known as "Huygens' law"), though he most likely did not use the exact same notation and methodology that are presented in our articles. I understand the apparent circularity, but I think the issue can be resolved without resorting to the modern physics invoked below. In principle, one can analytically determine regular periodic behavior of certain dynamical systems, without ever needing to have a good clock. In practice, a physicist might measure the accuracy of a quartz watch against an atomic clock - but in that case, the latter is known to be more accurate theoretically, and there is no strong need for purely empirical comparisons of which clock is more accurate. Still, if handed two mechanical watches and not allowed access to any other known clocks, it is an interesting and challenging thought experiment to devise a purely empirical way to determine which is more accurate... at the moment, the best I can come up with is to compare the time at sunset of the watches over a few weeks' time, and use what we can tell about sunset times from first principles. But I don't think that would work for distinguishing which of two modern quartz watches is more accurate. SemanticMantis (talk) 17:43, 14 May 2015 (UTC)

You may be interested in this article and this one. Count Iblis (talk) 15:03, 14 May 2015 (UTC)

Two fairly recent papers (2008, 2009) by cosmologists Andreas Albrecht and Alberto Iglesias (UC Davis) where a concept called "clock ambiguity" seems to play a central role. Thanks, but... whew! Is there a way you could give an idea of what that "clock ambiguity" thing is? There's nothing in WP regarding "clock ambiguity", while a Google search gives as the two top results precisely the two papers you suggested. In any case the concept, if it was not defined by Andreas Albrecht, seems at least to be firmly attached to his name. Oh, and while you're at it, is there a way you could summarize for dummies the basic ideas of those papers? Incidentally I'm surprised how recent those papers are. One would have expected such questions would have been settled long ago. Contact Basemetal here 15:57, 14 May 2015 (UTC)

I think your two questions answer each other. If you get more easily explainable experimental results using clock A as your standard than clock B, that's reason enough to prefer clock A as the standard of time. It's the only reason to prefer clock A, in fact; there's nothing else that "more regular" could mean independently of that. If the two clocks were the only things you could observe, there would be no way to decide which was better (and it would be meaningless anyway), but in reality there is a huge number of interrelated observations that we can make, and it's enough to form a consensus. In principle it would be possible to have no single consensus, e.g., to have two time standards that are each more accurate than the other with respect to many physical phenomena, but in practice that hasn't happened. Maybe it's true in a way of atomic versus solar time, but that's rather one-sided since we can explain the variation of the solar day in terms of the more fundamental atomic time. -- BenRG (talk) 18:05, 14 May 2015 (UTC)

Simplified answer to question 1:

• To check whether a phenomenon is regular, one can build multiple clocks built upon that phenomenon and compare them to each other . Thus it is easy to empirically show that human heart rate < pendulum swings < quartz crystal oscillation < electron transition frequency in regularity.
• Now, the question arises as to how we know that atmic clocks are truly measuring "time". It is possible that they are actually (whatever that means) varying randomly all over the place but because everything else in the world, for some reason, varies by the same rate too, we never notice or can even know that. Here I think we appeal to Occam's razor and. just like early 20th century physicists, argue that since such purported random variations are an unobservable phenomenon, we can safely ignore them in our theories of the world. Compare from, the debates that led to the rejection of luminiferous aether as the medium for the propagation of light.

PS: One could make the semantic argument that "transition between the two hyperfine levels of the ground state of the caesium 133 atom." are regular by definition, but that would be begging the question. Abecedare (talk) 18:19, 14 May 2015 (UTC)

Do you mean comparing multiple hearts, multiple pendulums, etc. by measuring them by one another? A more regular phenomenon would give more consistent results when you compare multiple clocks based on the same phenomenon? (Or you could take that as a definition of what "more regular" means?) Contact Basemetal here 19:07, 14 May 2015 (UTC)

Do you mean comparing multiple hearts, multiple pendulums, etc. by measuring them by one another? Exactly. See Table 17.4 for such comparisons. They are likely deriving their numbers by comparing the various instruments to the best available standard, but comparing each time measurement device to another one of its own kind will produce numbers in the same ball-park (off by a factor of approx ${\sqrt {2}}$ essentially). Abecedare (talk) 19:21, 14 May 2015 (UTC)

Many thanks to all who responded. The work of Andreas Albrecht, mentioned by Count Iblis, deals with conditions that are more exotic (early universe etc.) than what I had in mind. If however you're curious about that "clock ambiguity" thing you can either read the two papers mentioned above (which, after reading their abstracts, I wouldn't even dream of trying) or you can try to get some sort of qualitative feeling for the ideas involved by reading this, or this, or watching his video in this series or this video. In the latter you can watch him break stuff on purpose while first pretending it was an accident. Abecedare first observed that "one needs to make some assumptions about physical laws being space and time-invariant but I am assuming that your question is aimed towards the practical end, and not aimed at the purely philosophical level" but later decided to delete that in order to keep things simple. He was right. The reason I'm quoting that deleted remark is that I thought I'd collect here, just for the record, two situations which would complicate the answer to my question. Since I mentioned Andreas Albrecht's "clock ambiguity" I thought I'd also mention what Abecedare referred to and later deleted. I hope that was OK. Contact Basemetal here 11:57, 15 May 2015 (UTC)

Resolved

Progress 59

Several days ago, RosCosmos announced that a technical report on Progress 59 would be released on May 13. I cannot find any news, any updates on NASA's International Space Station website, or anything on RosCosmos' website. Has anybody found this report, or a news story about it? I'm willing to slog through a translation, but an English language source would be appreciated. Nimur (talk) 14:11, 14 May 2015 (UTC)

Anatoly Zak's Russian Space Web article mentions some May 12 preliminary conclusions and states that investigations will continue at manufacturing sites starting on May 13 toward expected final conclusions on May 22. I assume that RosCosmos' May 12 release supersedes the May 8 announcement you linked. -- ToE 17:20, 14 May 2015 (UTC)

Do the depolarization or repolarization represent systole / diastole?

Can we say that the depolarization represent systole and repolarization represent diastole? For any answer, I'd like to see a source. Thank you. 149.78.38.232 (talk) 14:44, 14 May 2015 (UTC)

No, one refers to the change in electrical properties of the heart, as measured by electrocardiogram, while one refers to pressure differences caused by the beating of the heart, as measured by a Sphygmomanometer. Two different measurements of two different properties by two different devices. --Jayron32 15:25, 14 May 2015 (UTC)

Of course, but the question was about the the representation of them. The question is if in the normal person, when there is depolarization then occurs the systole. 149.78.38.232 (talk) 18:58, 14 May 2015 (UTC)

"Yes" is the answer to your question. See Cardiac action potential for our (fairly technical) article on the subject. Excitation–contraction coupling explains the process in a simpler way. Depolarization might also be useful. Tevildo (talk) 21:57, 14 May 2015 (UTC)

Pleasure

Serios Q not a trolly. What pleasure does a woman get by administering prostate massage?--86.171.5.155 (talk) 15:50, 14 May 2015 (UTC)

About $125. μηδείς (talk) 19:24, 14 May 2015 (UTC)

We do have Human sexual activity#Motivations which states, "a person may engage in a sexual activity solely for the sexual pleasure of their partner", but generally speaking, Wikipedia isn't really a good resource for subjective information regarding sexual acts and the nature of participants' pleasure. If you have genuine curiosity about various sex acts, I think you'll have better success on a dedicated forum. Fetlife, reddit.com/r/sex, or even the old alt.sex would be better venues for your questions. -- ToE 16:58, 14 May 2015 (UTC)

Could somebody remove the entirely inappropriate answer in this thread, this isn't a joke board, it's a Reference desk. The Rambling Man (talk) 20:03, 14 May 2015 (UTC)

If you mean Medeis's quip I disagree. This is indeed a Reference Desk but humor can lighten our hard work. We're not Androids. It'd be enough to small it, as is customary. Contact Basemetal here 20:43, 14 May 2015 (UTC)

It looks like the responses to the OP are all sourced and sincere. ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:04, 15 May 2015 (UTC)

And speaking of references, the Manchester-based OP here, as 86.176.8.227 (talk · contribs), asked the same question a couple of weeks ago. It was removed and that particular IP was blocked for a few days. ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:22, 15 May 2015 (UTC)

Permanent coma

If I was in a permanent coma but my wife wanted more children I heard you can get the semen out of an unconcious man. How is it done?--86.171.5.155 (talk) 17:07, 14 May 2015 (UTC)

See Prostate massage, Electroejaculation, and Semen collection#Humans. -- ToE 17:39, 14 May 2015 (UTC)

But depending on jurisdiction there needs to be some form of consent on the the man's part (living will or something simular). Dja1979 (talk) 20:36, 14 May 2015 (UTC)

Trains and speed limits

Unfortunately, since I asked the question about self-driving cars and speed limits above there was a 2015 Philadelphia train derailment in which excessive speed around a curve has been named the cause. It is said that it could have been prevented by positive train control or by some older technology that adds running time to the train. [2] What I don't understand is, why is PTC so expensive and difficult to implement? Much more easily than the Google cars, I'd think that trains could be equipped with a device that locates position by GPS and looks up the track limit from a database stored in memory. It might update via cell phone. I'd think you could make one for under $100, yet I'm reading that expanding PTS to all of Amtrak would cost nearly a billion dollars. I'd think for that price Google could rig every train with cameras that automatically look at track lights, switch positions, figure out which track is which so there are never any ambiguities with which speed limits to use, and in short make the engineer as obsolete as a taxi driver. But for now, why isn't there some really cheap way for a train simply to know that a curve is coming up and not to be going 100 miles an hour? Wnt (talk) 21:51, 14 May 2015 (UTC)

The recent fatal accident may prove to be the stimulus for mandating the protective equipment you have described. Up until this accident it was relevant to ask "What is the problem that is to be solved?" and "Has there actually been a serious accident that would have been prevented by this kind of system?" and "What is the highest-priority threat to safety that should be tackled with available capital?" Dolphin (t) 22:32, 14 May 2015 (UTC)

This was hardly the first train crash caused by excessive speed: see e.g. Amagasaki rail crash. Contact Basemetal here 22:40, 14 May 2015 (UTC)

+1 - December 2013 Spuyten Duyvil derailment ―Mandruss ☎ 23:00, 14 May 2015 (UTC)

While positive train control can enforce speed limits, its design scope is much larger. It is intended to provide dynamic situational awareness of track conditions and the locations and speeds of other trains, and then preemptively respond to prevent collisions and other accidents. I would assume that a lot of the price tag is tied up in the ability to keep track of the locations and speeds of nearby trains, etc. As you say, simply enforcing speed limits as a function of location shouldn't have to be nearly as expensive, but then Congress mandated a PTC system with a lot of complicated features. Dragons flight (talk) 23:15, 14 May 2015 (UTC)

For that matter, how did the train get going that fast in the first place? If I remember correctly, the only trains Amtrak has that are even capable of reaching 100mph are the Acela Express trains, which the derailed train wasn't one of. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 23:33, 14 May 2015 (UTC)

According to Northeast Regional, the average speed on that line is about 55 mph, but in segments they go as fast as 125 mph. The Acela Express is faster (both in average and max speed), but it doesn't seem like the Northeast Regional would be incapable of reaching 100 mph. Dragons flight (talk) 23:51, 14 May 2015 (UTC)

Oh. Thanx... Whoop whoop pull up ^{Bitching Betty | Averted crashes} 00:14, 15 May 2015 (UTC)

What's odd here is that the train reached that speed 7 minutes out of Philly northbound, while traffic in this area is usually quite slow. The conductor has lawyered up, and the press is reporting he doesn't remember the accident. Anyone who's ridden that line knows that the quick acceleration out of 30th Street Station and such a speed in that area are highly unusual circumstances. The Acela concept is really more of a marketing issue with trains that are not especially fast, but which are certified safe to go at top speed for much of an express route with fewer local stops. The trip from Philly to Boston is 7 hrs on Amtrak, and 6 on Acela, maybe 8-9 on a local train that makes all stops in Connecticut. μηδείς (talk) 00:32, 15 May 2015 (UTC)

Note: a train conductor does not drive the train. The person who does that is the engineer or driver. --174.88.135.200 (talk) 07:09, 15 May 2015 (UTC)

Well, in that case the conductor doesn't need a lawyer. :) μηδείς (talk) 17:27, 15 May 2015 (UTC)

Getting back to Wnt's original question, the technology certainly exists in the aviation environment and at an affordable cost. Equipment called Enhanced ground proximity warning systems and Terrain awareness and warning systems are installed in most passenger-carrying aircraft but they only provide aural warnings to the pilots. A system called a Stick pusher is intended to over-ride the pilot, at least for a few seconds, so that regardless of what the pilot is trying to do, the system will forcefully intervene and stop him or her doing what could be too risky. I agree with Wnt that systems of this kind should be available for rail systems. It is likely such systems are already installed in the state-of-the-art locomotives, but retro-fitting them to older locos is more of a challenge, both technologically and economically. Dolphin (t) 00:54, 15 May 2015 (UTC)

• The difference is between conceiving of a solution, and implementing it at scale. For example, from NYT, "One major issue is that each freight railroad has its own tools but needs to make sure that its technology can communicate when traveling on tracks owned and operated by others. For the freight industry, positive train control involves fitting 36,000 wayside units and equipping 26,000 locomotives, according to industry figures." And, according to the same article, the Association of American Railroads estimates the cost of implementation to be $10 billion (those are trade-group figures, so you can expect some larding). Also second Dolphin51's point about retro-fitting being costlier, and Dragons flight's point that PTC is more than a speed-limit enforcer.

Possibly related: Although they are not talking about PTC per se, read Alan Levy and Stephen Smith on bloated rail infrastructure costs in US. Abecedare (talk) 01:25, 15 May 2015 (UTC)

See also this new New York Times article that lists several other practical implementation issues such as wireless spectrum availability,, inter-operability requirements, FCC regulations, congressional funding, equipment shortage etc. Abecedare (talk) 04:47, 15 May 2015 (UTC)

A caller to Dennis Prager yesterday, who identified himself as a retired engineer from CSX, said that two engineers in the cab is an industry standard, but that there was something about the original set-up of Amtrak's contract that allowed for one engineer only (what was implied was this was a cost-cutting measure). This is from a radio show, and not my area of expertise but this was an issue in NYC when the MTA did away with mid-train conductors who watched the platform, leaving only the drivers to man the train. μηδείς (talk) 17:34, 15 May 2015 (UTC)

An added wrinkle to this story now is the possibility of external sabotage. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:31, 16 May 2015 (UTC)

A police officer arrives at the scene of a single-car crash, the car is overturned and laying in a ditch.

Officer to driver: "This is a 50 mph zone. Why did I clock you at 107 mph right before you rolled over?"

Driver to officer: "Someone threw a stone at my windshield!"

μηδείς (talk) 17:45, 16 May 2015 (UTC)