Wikipedia:Reference desk/Archives/Science/2014 July 21

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July 21

Time loops

Could time loops actually exist in real life? Clover345 (talk) 00:05, 21 July 2014 (UTC)

Probably not, but existing theory doesn't currently completely rule out that possibility. There do exist solutions to the Einstein field equations which contain closed timelike curves, but those solutions generally require circumstances which have never been observed, and hence may never exist. See also Chronology protection conjecture. Red Act (talk) 01:54, 21 July 2014 (UTC)

See Time loop. The Novikov self-consistency principle is needed to avoid paradoxes, such as the Grandfather paradox, arising if a Closed timelike curve (CTC) existed. Most physicists feel that CTCs are artifacts. 84.209.89.214 (talk) 15:31, 21 July 2014 (UTC)

On the contrary, this assumes a classical (i.e. nonquantum) approach. I recall reading an article in Scientific American many years ago in which a quantum approach resolved this by showing that natural solutions existed, without having to resort to paradox-avoiding principles. My own guess is that this would be easiest understood in the Many worlds interpretation. I would tend to de-emphasize the statement about "Most physicists ..." in this context. —Quondum 18:43, 21 July 2014 (UTC)

The main thing I want to know about a time loop is the entropy of an isolated system within the loop. Either it's a theorem that you can't keep the system isolated (Novikov forbids it) or else the "direction of time" within the loop should reverse to point from the lowest-entropy point to the highest-entropy point, at least within the isolated system. Right??? Wnt (talk) 18:57, 21 July 2014 (UTC)

I disagree – you're coming at it from the perspective of being able to assign an entropy density to a point on the spacetime manifold. However, entropy is essentially specific to each observer, which is essentially connected to a what could be called a history (I don't know the terminology in MWI, so I'm improvising). Thus, an observer can see a different entropy on each circuit, even assuming a GR-like manifold. Remember that an observer does not see the "whole" wavefunction. An observer on each loop sees different histories (pasts).

Disclaimer – I'm headed into speculation here; my point is simply that the converse should not be taken as a given. —Quondum 00:10, 22 July 2014 (UTC)

In fiction I've seen this problem overcome by having a piece of information make the loop, not a physical object. For example, a document is transcribed then sent back in time to become its own source document. This prevents the problem of wear and tear on an "infinitely" old object. Katie R (talk) 19:33, 21 July 2014 (UTC)

da ja vw is a time loop . Thanks water nosfim

Some history questions about the ECG development

Hello everybody, I have some questions about the history of the EKG, and I would like to know the answers. 1. In the book "Dubin: rapid interpretation", written that "Galvany knew that the closing circle between two metals to dead frog's leg, creates an electric current". According to this thing, if someone takes a gold and silver for example (two different metals), his legs dance... but it does not happen in the reality. if so, what is the explanation for the things that mention above? 2. There written too "Koliker and Muller recover that when putting a motor nerve of grog's leg on a beatting heart, then the leg moves according to the beats", it does not clear to me what kind of heart he's talking about, Is it talking about human heart, and how they did that (what is the way they did it to approach to the beatting heart in order to make their research? מוטיבציה (talk) 02:40, 21 July 2014 (UTC)

Rapid Interpretation of EKG's by Dale Dubin is a long-time best-selling textbook.

EKG#History is another place to start reading. EKG or Electrocardiography is the study of natural electric signals in the living body. You have been reading about the much older experiments on reactions of muscles to externally applied electricity that were started by Luigi Galvani. Two different metals placed in contact can produce an electric voltage; some pairs of metals are useful for sensing temperature or for controlling corrosion. Gold+silver together generate very little voltage, too little to demonstrate a galvanic reaction on a person (though I suspect your book's author was joking). However be assured that if one joins sufficiently many Electrochemical cells in a series circuit to get enough (over 100V) potential, it will make anyone's leg "dance involuntarily". Koliker and Muller's work is cited in History of Defribrillation that you can view at the link. 84.209.89.214 (talk) 13:55, 21 July 2014 (UTC)

Thank you for your help. 194.114.146.227 (talk) 14:51, 9 August 2014 (UTC)

which is the top,best institute to get trained on "Telecom Protocol Testing" course in india?

am a b.tech e.c.e fresher(2014) without any experience in any field,kindly please suggest the top,best institute to get trained on "Telecom Protocol Testing" course in india?

I would suggest that you finish your electrical engineering degree first. This should include units about communications protocols. An employer will very likely give on the job training on how to use the equipment and facilities they have for testing. Any course you do now will probably be dated by the time you are employed. But on Wikipedia you can read Bit error rate test jitter loopback test, Ping (networking utility), traceroute, Optical time-domain reflectometer all the topics linked from Interference (communication) to get an idea. If you want to go further to prove yorself, you could write a page for Wikipedia on a related topic. Graeme Bartlett (talk) 22:54, 21 July 2014 (UTC)

Importance of Coking Coal

Why is coking coal the only form of carbon useful for steel manufacture? Why can't it be substituted with other carbon sources like graphite or dehydrated sugar [1], etc. 202.155.85.18 (talk) 09:43, 21 July 2014 (UTC)

Coking coal is about $100 / ton. Mineral derived graphite is about $2500 / ton (plant-derived graphite is even more). I don't think it is that one can't ever use other carbon sources, but rather that they choose to use the cheapest carbon source available that is also pure enough that it won't impact the steel too much. Dragons flight (talk) 09:55, 21 July 2014 (UTC)

Coke used to be cheap in the UK too, but it's now four or five times the US price if Dragons flight's estimate is accurate. Perhaps it's because we no longer make town gas here. Sugar is not much more expensive here, but unsuitable in its hydrated form. Dbfirs 20:49, 21 July 2014 (UTC)

For manufacture of low-carbon steel, gas can be used as well... 24.5.122.13 (talk) 00:03, 22 July 2014 (UTC)

High purity carbon is made easily and cheaply from charcoaled coconut husk in equatorial countries. This is used for carbon absorption like in CIL/CIP gold production. I can't imagine that it's more expensive than coking coal. Is there a particular reason why it may be unsuitable? 202.155.85.18 (talk) 00:44, 22 July 2014 (UTC)

Never mind...it turns out it is used [2]. 202.155.85.18 (talk) 01:03, 22 July 2014 (UTC)

Because there ain't no coconuts here in the USA (nor in England, last time I checked, unless that global warming thing really kicked in over there). 24.5.122.13 (talk) 04:04, 22 July 2014 (UTC)

You may want to be careful about claiming there are no alternatives as a previous contributor seemed very concerned [3] about such claims Wikipedia:Reference_desk/Archives/Science/2014 April 1#Wired can't figure out cleansteel. Anyway as others have said it's not necessarily impossible to use other methods [4] [5] [6] [7]. It's more that these methods aren't used much because of cost and similar reasons compared to total annual production [8] (and I believe in the earlier discussion there were figures of 74 million vs about 1.5 billion total production). So as evidence by the previous sources and others like [9] (and of course this infamous article [10]), there's great disagreement over whether it's realistic to expect coke to be substanially replaced in steel production in the next 20 years or so. (And of course, if it is replaced, whether it will be smelting iron with some other carbon or whatever reducing agent whether non renewable like shale gas or renewable like something plant derived, or whether some other method like electrolysis could be used.) Nil Einne (talk) 14:21, 22 July 2014 (UTC)

As I already pointed out above, there are alternative processes which use syngas instead of coal as the reducing agent. And of course it's theoretically possible to use electrolysis, but this is so expensive as to be utterly uneconomic at present (not to mention that most of the electricity it would use is generated from coal anyway...) 24.5.122.13 (talk) 04:18, 23 July 2014 (UTC)

Strength training

Does resting too long between sets during strength training lower it's effectiveness? Why? -- 90.201.185.224 (talk · contribs) 10:59, 21 July 2014 (UTC)

Define "too long". ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:02, 21 July 2014 (UTC)

I tend to rest several decades between sets, and that does, indeed, appear to lower it's effectiveness. StuRat (talk) 16:13, 21 July 2014 (UTC)

It ultimately depends on your goals. When you say "strength training" do you mean, literally, that you are seeking to increase strength in the sense of powerlifting, or do you mean it in the sense of weight lifting, in general? At any rate, the general rule (I'll dig up sources later, I'm at work and not able right now to give more than a few random articles) seems to be that shorter rest periods (say 1 - 1.5 minutes) with high intensity around 8 - 12 reps per set is idle for hypertrophy due to growth hormones, whereas for increasing strength, heaver weights (3 - 5 rep range) with 3 - 5 minute weight periods; this will allow you to do more reps. According to bodybuilding literature, the first is more geared towards sarcoplasmic hypertrophy (more massive) the latter myofibrillar (strength) - although, neither occurs in isolation from the other, it's more a matter of what you want to focus on most, though. At any rate, take all of this with a grain of salt, I've read a lot on the topic, but this is also from memory and typed in a rush. Finally, be aware that these are guidlines that have some support, but ultimately, what is "too much" or "too little" of anything will be a matter of your body, your diet, and your goals - you would be best served talking to a trainer, or just trying various regimes for 4 - 6 weeks and seeing the results over time. Heres a few articles, when I get more time, I'll find some better sourcing for you: [11], [12], [13], [14]. (As mentioned, these are by no means "definitive", take what I say with a grain of salt.).Phoenixia1177 (talk) 13:59, 21 July 2014 (UTC)

Power source

It took many hundreds of years before the invention of electricity, is it envisaged that someone, at some far future date, will invent an entirely new source of power?85.211.132.74 (talk) 12:41, 21 July 2014 (UTC)

We don't answer requests for opinions, predictions or debate. 84.209.89.214 (talk) 12:54, 21 July 2014 (UTC)

There are a few tidbits mentioned in Energy development. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:20, 21 July 2014 (UTC)

Electricity isn't a "source of power" - it's a means for transmitting energy from one place to another. For example, from the energy produced by spinning water turbines in the Hoover Dam is transmitted to the caps-lock LED in your keyboard by electricity. The electricity wasn't the source of the power - that was the water spinning that turbine.

We certainly do have other means to transmit power - for example, the Seattle Steam Company makes steam by using natural gas as an energy source, using it to boil water - and then pipes the resulting steam to local businesses, where it's used to provide heating. No electricity is involved - the energy is transmitted by the steam.

Electricity is a very convenient way to transmit power because we've figured out ways to convert almost any energy source into a flow of electricity - and to use a flow of electricity to power almost any kind of device we can think of. But it's not always the most efficient way - as the Seattle Steam Company have proven. But considered more broadly, an oil pipeline is another way to transmit energy. When you buy candy in your local store and bring them home for your consumption - you're transmitting energy (in the form of food calories) from the store to the place where it's going to be converted into body heat, body motion and brain activity.

SteveBaker (talk) 14:22, 21 July 2014 (UTC)

One could argue that it was nature that invented electricity, we just figured out how to exploit it. The reason it exists and the reason we can exploit it ultimately lead back to the Big Bang. It reminds me of a Carl Sagan statement: If you wish to make an apple pie from scratch, you must first invent the universe. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:33, 21 July 2014 (UTC)

Most people would say that we "discovered" electricity - just as we "discovered" fire. We generally reserve the word "invented" for things like 'The Wheel' - or 'The Internet' which didn't already exist in nature. SteveBaker (talk) 14:55, 21 July 2014 (UTC)

"We don't answer requests for opinions, predictions or debate. <IP address misappropriated>" Apparently not!!

I see, like nature created water power, but humans invented the gristmill and the hydroelectric dam. So maybe the OP's question comes down to whether new energy types might be invented in the future, i.e. if we haven't thought of everything yet? Electricity is generated by a variety of technologies, some old, some new - but it's still electricity. There could be additional fuels for generating electricity which we haven't discovered or made practical yet. But I think the OP is asking whether we have any clue of something that could replace electicity itself. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:24, 21 July 2014 (UTC)

Is there anyone already working on alternative forms of energy transmission? The OP refers to electricity as a "source of power" but I'm not sure this phrase encompasses everything they intend and I can't think of a better one. Would you call the electrons moving around a circuit a "source of power"? Circuits can operate using lasers, right? So light could be a "source of power" in the future, beyond the manners in which it already is? Could long-distance light transmission ever compete with electrical energy transmission in terms of efficiency? Could quantum entanglement play a role in energy transmission and conversion to work? --129.215.47.59 (talk) 14:18, 21 July 2014 (UTC)

Sitting in your home, electricity can be thought of as a "source of power", although that's not true in the big picture. The OP has made only two entries - the original question here, and 5 days ago about the possibility of creating giant batteries.[15] That suggests he's talking about ways to produce electricity rather than alternatives to electricity. But until he returns and comments, it's hard to know for sure. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:03, 21 July 2014 (UTC)

Note that people have been using electricity for thousands of years, although only a few people, and only as a "magic trick". Ancient clay pots seem to have been electrical cells, using acid (vinegar or lemon juice, perhaps), metal plates, and electrodes to create sparks on demand. Not sure if they hooked it up to an electric filament, but, if so, they would have had electric light, at least until the filament burnt up due to the lack of vacuum around it. Of course, an oil lamp would have been far more practical, at the time. StuRat (talk) 16:19, 21 July 2014 (UTC)

In terms of new stuff, there are people looking into using Spintronics as an alternative to electronics - where the spin of the electron is used instead of the charge. I'm not sure if that helps you with energy sources - or ways to transmit energy though.

My problem here is that the OP is asserting that electricity is the "source" of the power...if we're talking about power sources, then sure, we invented ways to use nuclear power (both fusion and fission) long after electricity was discovered and tamed. If we're talking about how energy is TRANSMITTED then we routinely transmit small amounts of energy in fibre-optics or using radio waves but also in larger quantities: A microwave oven transmits power through the air into your food using microwaves. The laser cutters my wife uses in her business transmit about 100 watts of energy through a beam of infra-red light over a distance of around ten feet.

So we have come up with plenty of new power sources - and new ways to transmit power - since the discovery of electricity...which leaves me puzzled as to why our OP thinks that electricity is the most recent discovery in that field. SteveBaker (talk) 16:50, 21 July 2014 (UTC)

StuRat: I think you are referring to the Baghdad Battery, which, according to Wikipedia's article, is no longer believed to have been electrical by mainstream archaeologists. הסרפד (call me Hasirpad) 02:18, 22 July 2014 (UTC)

" We don't answer requests for opinions, predictions or debate. <IP address misappropriated> " Apparentlty not !!

• • Hearing someone chime in with "No one is allowed to answer this question" when it is an appropriate question is a little annoying, like hearing little birds squawking for no apparent reason. Edison (talk) 16:04, 22 July 2014 (UTC)
    • I agree. The questioner asks whether this "is envisaged" - and that's a testable proposition. Are there reliable sources to say that someone notable in the world of physics is envisaging some new power source - and presumably doing research in that direction. SteveBaker (talk) 03:09, 23 July 2014 (UTC)

• "Electricity" is not a source of power and was not invented, but electric batteries are sources of electric power, in the sense that they make electricity from a combination of chemicals. Generators are sources of electric power, in the sense that they translate a prime mover into electricity. Solar cells are a source of electric power as well. The electricity created by these devices is a type of power which has useful properties that the chemicals, the prime mover or the sun lack. In the sense of the OPs question, researchers are always trying to find new ways to convert something into electricity. Micropower describes devices which produce electricity from chemical fuel in a consumer device or a portabl military device, or which produce electricity from sound energy or other less useful forms of energy. Edison (talk) 22:45, 23 July 2014 (UTC).
  • How would you re-word the OP's question so that it makes proper sense? ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:50, 23 July 2014 (UTC)

• • • I can't - I truly cannot parse what the OP is asking. Are we being asked about new ways to TRANSMIT energy? (Electricity is one way - there are others, like the steam-heat system in New York or (in a sense) an oil pipeline or a fibre-optic cable) - or are we asking about brand new energy sources? (electricity isn't an energy source) Either way, the OP's question doesn't make sense. We need to be asked a question that makes sense. So perhaps:
      1. "What other ways of transmitting energy are being developed or are thought to be plausible in the future?"...or...
      2. "What other sources of energy are being developed or are thought to be plausible in the future?"
    • I can't find a way to wedge "electricity" into the question without destroying it. (1) can't refer to electricity as the only way we transmit energy right now because there are dozens of ways we do that. (2) can't refer to electricity because it's not an energy source. SteveBaker (talk) 04:51, 24 July 2014 (UTC)

But isn't electricity the only way we transmit energy over large distances so that it can be used for something other than heat? I can't be sure what the original questioner was asking but it inspires me to ask what potential forms of transmission of energy might arise from current or future research that can do useful work like calculations, display of entertainment or data, production of sound, washing of clothes, cooking of food. 129.215.47.59 (talk) 10:26, 24 July 2014 (UTC)

I take it you never played SimCity 2000? EM is an obvious possible alternative form of transmission. Microwave transmission#Microwave power transmission is most commonly suggested. Lasers are also sometimes suggested although usually only for specialised cases. We also have an article Wireless power which discusses these possibilities and more although it also discusses stuff like induction used for short transmission distances. Nil Einne (talk) 14:12, 24 July 2014 (UTC)

Natural gas can be used for things other than heat. It can be used to run a generator or fuel cell to create electricity, or can directly power heats pumps, etc., to provide cooling. It tends to be more reliable than electricity from the grid, is also maybe a third the cost of electricity per unit of energy, in many places, and fracking may bring the cost down further. StuRat (talk) 14:21, 24 July 2014 (UTC)

Yep, exactly. Electricity is the most convenient/practical way we have to transmit energy when we have no clue how it will ultimately be used. But we can also use an oil pipeline to transmit energy...it's really no different from an electrical power line, except that the energy that's delivered is a bit inconvenient to use. But as StuRat says, if we know in advance that you need the energy for heating your home or for cooking food - then we can use a gas line to pump "chemical energy" to your home in the form of natural gas - and (in some circumstances) it's actually cheaper and more convenient than burning the gas in a power station to generate electricity for you to heat and cook with. Electricity is also more convenient over longer distances - but there are limits. Exporting electricity from the USA to China would be exceedingly difficult - but sending them a tanker full of liquified natural gas is pretty easy. Over shorter distances, we use microwaves to convey energy from the microwave oven into our food - and over longer distances we use optical fibres to send tiny amounts of energy to convey information. Filling up your shopping cart at a supermarket and driving home with the food is also a means of conveying energy that is more convenient than electricity because we don't have good technology for using electricity to power our bodies.

Electricity is so ubiquitous because it's so easy to use it in such a huge variety of ways. We *could* build computers that ran off of natural gas...but we don't. You can buy refrigerators that work from gas - but electrical fridges are just more practical. Electricity is also a kind of 'universal currency'. Almost no matter what form of energy you start with (oil, gas, coal, wind, solar, nuclear, hydro, etc) - you can convert it to electricity that's compatible with everyone's homes and factories. Converting nuclear energy into natural gas would be a nightmarishly difficult task! Even if we wanted to use wind energy to run your toaster, we'd have to convert it into electricity first.

So, I'm coming to think that the right question here - is more like "Electricity is the universal 'currency' in which energy is exchanged - is there an alternative 'currency' that we could use instead?"...and that's a really interesting question! We COULD use big lasers to transmit energy down long tubes to factories, offices and homes - and then we could use small optical fibres to convey a small portion of that light to light our houses and to heat up food...but using laser light to directly run a refrigerator, wash dishes, replay music...that would be tough! You'd end up converting most of it to electricity first. Similarly, we can convert heat into electricity using steam turbines - so nuclear, coal, oil and gas can be converted easily - but converting those forms of energy into light seems impossible without first converting it to electricity. I can't imagine a form of energy that's remotely as interchangeable as electricity...which is why it's become our standard for general-purpose use...and the other things are relegated to niche usages.

SteveBaker (talk) 17:39, 24 July 2014 (UTC)

RE: "We *could* build computers that ran off of natural gas", I saw a funny sign at a gas station: "Laptops, $199, Diesel, $399". Of course, they meant they sell diesel fuel for $3.99 per gallon, but the thought of a diesel-powered laptop pumping out black smoke from it's smokestack as the user downloads porn gave me quite the steampunk image. StuRat (talk) 00:51, 26 July 2014 (UTC)

Gas lighting involves no electricity, nor does an Oil lamp. 84.209.89.214 (talk) 20:28, 24 July 2014 (UTC)

It's actually kinda amusing to imagine a world where forms of energy other than electricity were dominant. Suppose, for example, we used gravitational potential energy for everything. The turbines at the Hoover Dam would be modified to lift enormous weights to the top of large poles. These poles (complete with heavy weights on the top) would then be delivered to your home, where you'd allow the weight to slowly fall, while raising smaller weights throughout the house - like the ones in a grandfather clock. These would then have to drive various appliances. To cook food, you might have an enormous drum that would be rotated by a falling weight and would rub two high-friction surfaces together to make heat to cook with! Falling weights can easily turn motors - so your refrigerator's compressor would be spun by a falling weight too! You can think of all sorts of crazy contraptions that you'd need if gravitational energy (or kinetic energy) were to supersede chemical and electrical energy as our main way to transfer energy from one place to another. SteveBaker (talk) 17:49, 24 July 2014 (UTC)

Strength vs cardio training

Does strength training have the same health benefits as cardio training such as promoting good immune system health, heart health etc.— Preceding unsigned comment added by 90.201.185.224 (talk) 16:23 21 July 2014 (UTC)

Certainly not as much benefit for the heart as cardio, but still any exercise is better than none. StuRat (talk) 16:41, 21 July 2014 (UTC)

It's possible to overtrain or improperly train, and this can be unhealthy, even for athletes. UFC fights are routinely cancelled/changed for training injuries. That sort of exercise isn't better than nothing. Unfit people should always start off slower than fitter folks. InedibleHulk (talk) 03:05, 23 July 2014 (UTC)

Here are some references about how strength training can improve various aspects of heart health [16] [17]. The benefits of strength training for heart health seem to be different than the benefits from cardio. SemanticMantis (talk) 18:06, 21 July 2014 (UTC)