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November 3

Time is an illusion

Back when I was at school (not "abducted", sorry auto-correct error 46.229.161.232 (talk) 18:50, 5 November 2012 (UTC)), I got into a conversation with, well lets just call him "Ted". At some point, the subject turned to reality and the meaning of life. Ted started to explain his understanding of Time. He said that it was just an illusion, and that what we were experiencing was our conscious movement through the multiverse. He said that there is an infinite number of static Universes and that the illusion of Time was in fact the changes noted when passing though these static universes. Was Ted pulling my leg, or could this be true? 46.229.161.232 (talk) 01:34, 3 November 2012 (UTC)[reply]

Welcome to the Science Reference Desk. Do you need help finding a reference to scientific question? If you need assistance finding a general forum for discussion, please see our article on internet chat room. Nimur (talk) 01:47, 3 November 2012 (UTC)[reply]

I'm un-hatnoting this. I see nothing medical involved. Besides, I agree with Ted. :) (Oddly enough, I just linked to my comments in this regard in the "free will" thread on the Humanities Desk) I should disclaim, however, that things beyond the universe tend to be inaccessible to scientific investigation, so this may not be the right subsection for the question. Wnt (talk) 02:26, 3 November 2012 (UTC)[reply]

Quoting from Scientific American,

...the true arena of events in a relativistic universe is a big four-dimensional block. Relativity appears to spatialize time: to turn it into merely one more direction within the block. Spacetime is like a loaf of bread that you can slice in different ways, called either “space” or “time” almost arbitrarily.

The concept of time that you describe is one that some physicists believe in, or believe is required according to certain models of how the universe works. However, it's not actually obvious that this interpretation is true, testable, or even meaningful. At this point in...time, it seems like just a philosophical interpretation of physics, and one that's not universally held. Someguy1221 (talk) 01:51, 3 November 2012 (UTC)[reply]

While physicists rely on time being real in many of their formulas, one thing that does seem odd to them is the unidirectional movement of time. Nothing in physics limits time in this way, and the 3 other dimensions go both ways. StuRat (talk) 02:19, 3 November 2012 (UTC)[reply]

Time is real, but in a couple of months Newsweek will be an illusion. As regards backwards time travel, has anyone found any evidence confirming it? ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:23, 3 November 2012 (UTC)[reply]

If the OP is suffering from illusions he needs medical attention, not bullshitting. μηδείς (talk) 02:35, 3 November 2012 (UTC)[reply]

Only if he's not making it up. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:14, 3 November 2012 (UTC)[reply]

In other words, feed the birds, not the trolls. :-) 24.23.196.85 (talk) 03:35, 3 November 2012 (UTC)[reply]

Per Refdesk guidelines, please don't diagnose the visitors. The notion that a person must live his entire life in strictly the physical world, without ever experiencing a single vision, prophecy, revelation, or paranormal experience, or else be branded as permanently psychiatrically damaged, seems to me to be an extreme excess of materialism. Wnt (talk) 03:55, 3 November 2012 (UTC)[reply]

I much prefer this version of feed the birds ;-) Dmcq (talk) 10:35, 3 November 2012 (UTC)[reply]

Clearly a troll question, or at best a question with no good RD answer. Let's stop feeding please. Shadowjams (talk) 04:38, 3 November 2012Comment moved here after unhatting by Someguy1221 (talk) 04:53, 3 November 2012 (UTC)[reply]

Time is an illusion, in the sense that the traditional interpretation of time that the past and future are not real and only the present moment is real, is wrong (not just in relativistic physics, also in classical mechanics and quantum mechanics). The burden of proof is on those who believe that time does exist to prove this, not the other way around. If something does not exist, then there is nothing to prove.

Any set of laws of physics where information is conserved will have this property. If the information about the past exists in the future without any of that getting lost, then the past exists inside the future state. E.g., in principle you can measure who wins the US elections. The practical problem with performing such a measurement is that it involves a complicated interaction with every particle located in a sphere of about 4 lightdays radius. But the known laws of physics allow you to perform that measurement, which will collapse the wavefunction of the World into that state that under the time evolution will evolve to the state consistent with your measurement. Count Iblis (talk) 04:52, 3 November 2012 (UTC)[reply]

Time is an illusion; lunchtime doubly so. 82.131.132.190 (talk) 22:45, 3 November 2012 (UTC)[reply]

Time being an illusion is not an uncommon idea in philosophy. The nature of time is a complex topic, both in physics and in philosophy. You may find the following articles to be of interest: The Unreality of Time, Eternalism (philosophy of time), The End of Time (book), Arrow of time, Time in physics Red Act (talk) 00:07, 6 November 2012 (UTC)[reply]

A tidal dam for New York?

We have seen lately how vulnerable New York is to these types of hurricanes, especially thanks to global warming and sea-level rise.

I hope those subways and tunnels will get pumped out and operational again.

Especially since the hurricane, have the officials for the city of New York considered tidal dams to protect the city? London already has the Thames River Barrier so what obstacles must New York surmount in order to install such barriers of their own?

1. Do we have an article on such concepts?

2. How much would such a barrier be estimated to cost?

3. How big / what type of political obstacles are there?

4. What other obstacles and considerations would they need to evaluate and overcome in order to get the tidal barrier installed around the city?

Good golly, I really hope plans for such barriers are being put forth in city board meetings these days because we can't expect these storms to get any gentler in the future. The sea-level rise coupled with land subsidence due to heavy skyscrapers and etc. will make such sea barriers imperative for the city's future. --Let Us Update Wikipedia: Dusty Articles 07:35, 3 November 2012 (UTC)[reply]

It might help in the short run, but, eventually, any such barrier will suffer a catastrophic failure as sea levels rise and storms become more severe. So, it might result in a false sense of security, ultimately leading to more deaths, similar to the levee failures in New Orleans when Hurricane Katrina hit. A more sensible approach, IMHO, is to use any funds slated for a barrier to rebuild on higher ground, further inland, as anything that flooded this week will surely flood again, barrier or no barrier. StuRat (talk) 07:41, 3 November 2012 (UTC)[reply]

The Geography of New York City is very different from that of London. Where are you proposing to place your barrier(s)?--Shantavira|^{feed me} 08:03, 3 November 2012 (UTC)[reply]

There isn't much subsidence risk in NYC. London is built on clay, which is good for tunnelling, but only moderately good for skyscrapers. New York, on the other hand, is built on granite. This is why its underground network is so much shallower than London's, but it can support awesome skyscrapers. Even PATH, which is much deeper than most of the subway, is only as deep as the foundations of the WTC.

As for a barrier, well, one could put one in the Narrows, but that wouldn't protect Staten Island, southern Brooklyn, or Rockaway. If you put a much longer barrier between Sandy Hook and Rockaway, that might well worsen the flooding risk to Rockaway and coastal New Jersey, while costing a huge amount for something that's not used often. Obviously if the frequency of such storms increases, this might have to be reconsidered. AlexTiefling (talk) 09:56, 3 November 2012 (UTC)[reply]

Another solution is to let water flow freely. That has worked for Venice for ages. Comploose (talk) 13:24, 3 November 2012 (UTC)[reply]

No, it hasn't. See Venice#History and MOSE Project. Rmhermen (talk) 13:59, 3 November 2012 (UTC)[reply]

In fact, they had some serious flooding just this past week.[1] ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:50, 3 November 2012 (UTC)[reply]

See here. And along the coast line where you don't have harbors, you can build dikes in the sea like this, so that you still have a beach. Count Iblis (talk) 16:28, 3 November 2012 (UTC)[reply]

There was an interesting article in GSA Today just last month on optimizing mitigation. See this. Zoonoses (talk) 02:28, 4 November 2012 (UTC)[reply]

Protecting Manhattan would require two such barriers, one at The Narrows to protect water entering New York Harbor from the south, and one to protect water from coming in at the East River, where there are several candidate locations: City Island, Bronx would provide probably the farthest practical point, beyond this Pelham Bay is probably too large to be feasible. Throggs Neck is also feasible, and would protect most of northern Queens and the South Bronx as well, while the confluence of Hell Gate and Bronx Kill near the northwestern tip of Randall's Island is probably the narrowest point, and closest to Manhattan, one could build it. Any flood control barrier south of the Narrows or east of the East River would likely cross too large a stretch of water to be feasible. --Jayron32 05:42, 6 November 2012 (UTC)[reply]

The best enzymes for ligating DNA:

The best enzymes for ligating DNA

Select one:

a. come from humans, as they are compatible with the most complex types of DNA.

b. come from bacteriophages, as they don't need to be incubated at a specific temperature to work.

c. come from thermophilic bacteria, as they need to survive thermocycling.

d. come from retroviruses, as they integrate their own DNA into a host's genome most efficiently.

(a) seems unlikely, but doesn't this seems like a subjective question anyway? 130.56.94.164 (talk) 13:17, 3 November 2012 (UTC)[reply]

(a) is clearly the correct answer, as humans are the most evolved species living on earth. Except for those who try having others do their homework. 77.3.129.83 (talk) 13:53, 3 November 2012 (UTC)[reply]

I don't know the answer, but our article on DNA ligase indicates that the most widely used type for lab work comes from bacteriophage T4. Looie496 (talk) 16:27, 3 November 2012 (UTC)[reply]

How would you do this?

You are given a plasmid with Ampicillin resistance, and a recombinant GFP gene engineered to only be expressed in the presence of lactose. Explain how you would get this vector into E. coli and screen for successfully transformed cells without using UV light. --130.56.94.164 (talk) 13:27, 3 November 2012 (UTC)[reply]

Not only does this question read as a homework question copied out, and we are not here to do your homework for you, it is impolite to post a question without giving a name. A psuedonym will do, but please assign yourself a name. Wickwack 60.230.220.27 (talk) 15:07, 3 November 2012 (UTC)[reply]

Is a name really a requirement here? It looks like new rules are generated every minute. But OK, I'll sign WickedWhack 77.3.129.83 (talk) 15:18, 3 November 2012 (UTC)[reply]

As far as I am aware there has never been a requirement for an IP to invent a name for the purposes of asking a question at the RefDesk. IP editors are just as welcome here as account holders. We won't do your homework for you, but you don't have to jump through any extra hoops in order to ask, and you were not being impolite. - Ka renjc 19:05, 3 November 2012 (UTC)[reply]

We have articles on Ampicillin, I have made a redirect for Ampicillin resistance (which goes to a stub which you can expand given the inclination), and we also have articles on Beta-lactamase, there is a MeSH code: MeSH G12.392.269.347.500.600.050, pComb3H, pGLO, plasmid, Green fluorescent protein (for GFP) and Escherichia coli (molecular biology). Graeme Bartlett (talk) 04:09, 4 November 2012 (UTC)[reply]

Inoperability of back-of-neck skin?

"As he aged, starting in the late 1970s, Kim developed a growth on the right-back of his neck which was a calcium deposit. Its close location near his brain and spinal cord made it inoperable. Because of its unappealing nature, North Korean reporters and photographers, from then on, always shot and filmed Kim while standing from his same slight-left angle to hide the growth from official photographs and newsreels, which became an increasingly difficult task as the growth reached the size of a baseball by the late 1980s."

I'm missing something here. Why couldn't they just operate on it like any other skin condition? Nyttend (talk) 13:42, 3 November 2012 (UTC)[reply]

I'm not quite clear what is meant by a "calcium deposit" but I suggest that the reason they give is not the real reason, (North Korea has some history in this department) Maybe he had a surgery phobia. It is possible he had one of [http://www.ispub.com/journal/the-internet-journal-of-dermatology/volume-6-number-2/giant-sebaceous-cysts-of-scalp-a-case-report.html#sthash.8timQ2ox.dpbs these (scroll down a bit)]. By coincidence the first reference at the bottom of the page is from four Korean medics, so they are possibly common in Korea. Richard Avery (talk) 15:24, 3 November 2012 (UTC)[reply]

Are there any pictures? Given his obesity and habits it could also have been a gout tophus, although I think they are usually associated with joints. μηδείς (talk) 17:58, 3 November 2012 (UTC)[reply]

Sounds like an odd place for one, and when it is so far advanced as to lead to visible external tophi, gout is not a hard condition to diagnose or treat. I assume Kim had access to some kind of medical care. Wnt (talk) 13:36, 4 November 2012 (UTC)[reply]

Ko's

How come in a boxing or mma fight, when people who get hit in the exact same spot get knocked out, some of them go limp, and some of them get stiff and rigid? Shoulden't the body react the same if they are hit in the same spot? --Wrk678 (talk) 19:57, 3 November 2012 (UTC)[reply]

I don't see why the body would react the same. The damage done could be different, depending on the force of the impact, tiredness, or on previous injuries. Comploose (talk) 20:00, 3 November 2012 (UTC)[reply]

I have a semi precious stone and I want to know what it is.

I have a stone that is light blue that glows orange in the light. Can anyone tell me what it is? — Preceding unsigned comment added by 216.36.16.221 (talk) 20:36, 3 November 2012 (UTC)[reply]

I don't know, but if you can post a picture it may aid others. Falconus^{p t c} 20:43, 3 November 2012 (UTC)[reply]

Could you be a little clearer about what kind of light you are using to see the glow? Is it daylight, ultraviolet light, or light from an incandescent bulb or a fluorescent tube? - Ka renjc 21:56, 3 November 2012 (UTC)[reply]

Sounds like fluorite to me, but it doesn't have to be. See what you think from the article. Wnt (talk) 22:08, 3 November 2012 (UTC)[reply]

I'm not absolutely sure that this is what the OP is talking about, but he or she may want to look at the lists in our pleochroism article. Deor (talk) 12:23, 4 November 2012 (UTC)[reply]

What is it the

As much as I try to understand what is it an electric charge, I can't understand it at all. What is it this charge? Is it a product or an effect of the magnet? מוטיבציה (talk) 21:07, 3 November 2012 (UTC)[reply]

It is a property of a particle, there are two kinds. Two electric charges of the same kind will push appart, two of the different kind will draw near. Unlike magnetism, the kinds electric charge can be found appart from one another. Plasmic Physics (talk) 22:34, 3 November 2012 (UTC)[reply]

Magnetism is caused by moving electric charge, so a magnet is an effect of charge not the other way around. As User:Plasmic Physics says electric charge is a property of some elementary particles. In most every day macro occurrences something that is negatively charged has an excess of electrons. Something that has positive charge has a lack of electrons (again I'm talking macro objects, this is due to protons, which have positive charge, being immobile in objects and electron being able to move). But there is only one type of electric charge (and it's anti charge) unlike colour charge which has 3 different types of charge (and there anti-charges).Dja1979 (talk) 01:04, 4 November 2012 (UTC)[reply]

Electric charge is something that causes an electric field. Electric charge is a property intrinsic to certain particles such as electrons, protons, and their antimatter equivalents. A moving electric field creates a magnetic field; conversly, a moving magnetic field creates an electric field. Without getting into the mathematics of the subject, there's not much point in trying to take it further than that. There are things that man does not have a visuallizable understanding of, and this is one of them. Physicists and engineers have long worked out mathematical models that verify and predict practical measurements. Once you have become accustomed to using the math, you become comfortable and confident with it, without ever really understanding the actual basis of the phenomena. Ratbone 124.178.138.168 (talk) 01:59, 4 November 2012 (UTC)[reply]

Thank you all for help. מוטיבציה (talk) 21:24, 4 November 2012 (UTC)[reply]

If you really want to get into it there's isospin and hypercharge, where I feel intuitively as lost as you do. Wnt (talk) 14:59, 5 November 2012 (UTC)[reply]

Gravitational potential energy

Start with two masses m1 and m2 at rest, separated by a distance r, and then release them.

At any subsequent (non-pathological) point, should the sum of the masses' kinetic energy (= 1/2*m1*v1^2 + 1/2*m2*v2^2) equal the change in potential energy, where potential energy is calculated using the forumla -G*m1*m2/r^2? 86.128.3.213 (talk) 21:47, 3 November 2012 (UTC)[reply]

The question appears to be asking if the sum of kinetic and potential energy in the system is conserved. In an ideal Spherical cow system, where there is no intervening gas or fluid and no electromagnetic effects, the sum of potential and kinetic energy should not increase or decrease. If the sum of potential and kinetic energy increased, we would seem to have a fine perpetual motion energy production device. The question does not specify that the masses are in a vacuum. If the total energy decreased, where did it go? If I release them in a zero G chamber filled with a gas or a fluid, they will do work as they converge and the sum of kinetic and potential energy at a subsequent point before impact would be decreased by the work done on the medium, which would heat the medium. Edison (talk) 22:55, 3 November 2012 (UTC)[reply]

Thanks, yes, I am aware of the principle of conservation of energy. My question is whether the numbers calculated by the above formulas ought to match, because in simulations I cannot get them to match. I wonder if there is some flaw in the reasoning of using those formulas in the obvious way, not whether there is some flaw in the principle of conservation of energy. You may assume no loss of energy due to other factors. The other possiblity is that I may be making a silly error that I cannot spot. Sorry if that was unclear. 86.128.3.213 (talk) 23:06, 3 November 2012 (UTC)[reply]

Yes, the numbers should add up. If they don't, please post your work, and we will see if we can find the error. StuRat (talk) 23:26, 3 November 2012 (UTC)[reply]

The program I am using is below. I am dumping it without a great deal of explanation, but I believe its operation should be fairly obvious to anyone who has a chance of finding the error which I have been unable to see. I do hope this isn't just some silly finger trouble.

G = 1.23 'arbitrary value; shouldn't matter
dt = 0.00001

m1 = 1
m2 = 10

'initial positions and velocities
x1_0 = 0
v1_0 = 0
x2_0 = 10
v2_0 = 0

'initial energies
ke_0 = 1 / 2 * m1 * v1_0 ^ 2 + 1 / 2 * m2 * v2_0 ^ 2
pe_0 = -G * m1 * m2 / (x1_0 - x2_0) ^ 2

'initialise variables
x1 = x1_0
v1 = v1_0
x2 = x2_0
v2 = v2_0
t = 0

Do

    r = Abs(x1 - x2)

    'calculate energies
    ke = 1 / 2 * m1 * v1 ^ 2 + 1 / 2 * m2 * v2 ^ 2
    pe = -G * m1 * m2 / r ^ 2
    dke = ke - ke_0
    dpe = pe - pe_0
    
'-----------------------------------------------------------
' at this point dke + dpe should equal zero (to reasonable accuracy), but it doesn't
'-----------------------------------------------------------

    'move one timestep
    t = t + dt
    F = G * m1 * m2 / r ^ 2
        
    a1 = F / m1 * Sgn(x2 - x1)
    v1 = v1 + a1 * dt
    x1 = x1 + v1 * dt
    
    a2 = F / m2 * Sgn(x1 - x2)
    v2 = v2 + a2 * dt
    x2 = x2 + v2 * dt
    
Loop

86.128.3.213 (talk) 02:22, 4 November 2012 (UTC)[reply]

This is expected, because you are calculating a solution using Euler's method. While this seems to be a simple and correct approach, it is well-known (amongst computational physicists, anyway) that Euler's method, applied to the formula for gravitation, propagates error, amplifying tiny calculation errors until they are exponentially larger than the quantities under consideration. Hold on, I'll dig up link to a page in our archives when I last discussed this topic. Nimur (talk) 11:57, 4 November 2012 (UTC)[reply]

Thank you for looking at this. I must admit that I am initially sceptical that the level of discrepancy I am seeing is due to numerical artefacts of the discrete approximation method. However, I know from seeing previous replies of yours at the ref desk that you are normally very knowledgeable, so I may have to stand corrected. 81.159.107.19 (talk) 12:07, 4 November 2012 (UTC)[reply]

Thank you for the compliment. But don't take my advice as authority: verify for yourself! Unfortunately, my link from the 2009 discussion is no longer active; the course website is now handwritten lecture notes with only a passing mention of Euler's method. There used to be an interactive applet, a breakdown of analytic and numerical sources of error, and all specifically for gravitation! No worries, there are other examples on the web, and I'll find some. And, all hope is not lost for your simulation: you'll just need to implement a different calculation method, such as a Runge-Kutta solver, that is appropriate for stiff equations like gravitation. The problem with numerical error isn't the roundoff or floating-point inaccuracy in any single calculation: it's the error that propagates from one step to the next. Each iteration of your loop amplifies a small deviation, and before long, you're very far from a reasonable solution. Let me keep looking for a suitable example on the web. Nimur (talk) 12:31, 4 November 2012 (UTC)[reply]

One of the reasons I am surprised is that I have used an essentially identical method to plot orbits, and it seemed to work very well (in terms of producing a sensible-appearing elliptic orbit). I have also used it to simulate n-body problems with visually sensible-looking results. See http://img834.imageshack.us/img834/5673/nbody.gif . 81.159.107.19 (talk) 12:50, 4 November 2012 (UTC)[reply]

Forget all the responses above, or at least, forget them until you read this one. You are calculating gravitational potential energy incorrectly. It is -G * m1 * m2 / r, not -G * m1 * m2 / r ^ 2; you're off by a factor of r. --140.180.252.244 (talk) 00:21, 5 November 2012 (UTC)[reply]

Good eye! The above post is correct. Fix that error, and then we can consider other issues like numerical accuracy. Nimur (talk) 02:45, 5 November 2012 (UTC)[reply]

ARRRRGH!! 140, I am so grateful to you. Fixes it perfectly. You have no idea the number of times I have looked through that code without spotting that. When I say "perfectly", I mean up to my expectations of accuracy for smaller t. Nimur, you are correct of course that sooner or later the method would start to diverge considerably. 86.146.108.178 (talk) 18:18, 5 November 2012 (UTC)[reply]

Maximum Age for Becoming a Father

Is there a maximum age at which a man can become a father like there is for women/mothers? Futurist110 (talk) 22:25, 3 November 2012 (UTC)[reply]

No, not quite, but they do have a "best before" date. Plasmic Physics (talk) 22:37, 3 November 2012 (UTC)[reply]

So a man aged 115 could theoretically naturally become a father if he wanted to (and had the energy to have sex)? And what is the "best before" age? I know that it has to do with the condition of sperm deteriorating over time, but I don't know the exact age. Futurist110 (talk) 22:40, 3 November 2012 (UTC)[reply]

I doubt there is any "exact age". It would probably be a continous curve, which would in any case probably vary significantly from person to person. 86.128.3.213 (talk) 23:08, 3 November 2012 (UTC)[reply]

This page outlines some of the risks associated with being an older father. See also Man is 'world's oldest dad at 94'. Alansplodge (talk) 23:46, 3 November 2012 (UTC)[reply]

Thank you. Based on the info in your link, it would thus appear that someone like Jiroemon Kimura could still have another child if he had the energy to have sex right now, but that the odds of this would be pretty low due to sperm deterioration over time. I wonder if someone aged 95+ ever tried having a child or not? Futurist110 (talk) 23:51, 4 November 2012 (UTC)[reply]

One risk is confusing the baby's diapers with your own. :-) StuRat (talk) 00:33, 4 November 2012 (UTC) [reply]

Sperm don't sit around like eggs. They are produced and degrade regularly. If oldsters can still produce them they will be new sperm. μηδείς (talk) 03:52, 5 November 2012 (UTC)[reply]

Nevertheless, some evidence has been reported that the sperm of older men is more likely to contain mutations that affect the children to whom they pass than the sperm of younger men, although the overall risk is still small. - Ka renjc 11:37, 5 November 2012 (UTC)[reply]

Yes, that's true, mutation load in the stem cells increases with age, and older men are more likely to be sterile for a host of reasons. Just want to make sure the OP is clear that unlike women's eggs they are produced anew at all stages of life and last for a short while, while eggs are produced early and once and then sit around for life til they are fertilized or go bad.

It has recently been reported that a 96-year-old man has fathered a child. Graham87 12:00, 5 November 2012 (UTC)[reply]

The original Dirty Old Man. -- Jack of Oz ^[Talk] 21:28, 6 November 2012 (UTC) [reply]

There were a Lot of dirty old men before him. StuRat (talk) 19:46, 7 November 2012 (UTC) [reply]

In fact, paternal age has been corelated with an increase of risk of the child being born with autism. Plasmic Physics (talk) 04:59, 7 November 2012 (UTC)[reply]

Yes, that's mentioned in the article that I linked above, It also mentions an increased risk of dwarfism, achondroplasia, schizophrenia and bipolar conditions, pre-term birth, genetic abnormalities and limb defects. It notes that in the US, there is an upper age limit of 40 for sperm donors. Alansplodge (talk) 14:12, 7 November 2012 (UTC)[reply]