Wikipedia:Reference desk/Archives/Science/2013 April 22

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April 22

Why are lasers dangerous?

In Surely You're Joking Mr Feynman, Feynman mentioned that it takes huge amounts of light to cause blindness if it isn't ultraviolet light, since each photon isn't carrying enough energy to do damage. He went as far as to look at a nuclear bomb explode through a car window, since that would filter out the ultraviolet light. Lasers only have one wavelength, so unless they're ultraviolet lasers, there will be no ultraviolet light. How do they cause blindness. Are they just that bright?

--— DanielLC 05:23, 22 April 2013 (UTC)

Lasers can indeed emit a lot of ultraviolet light, even when they aren't "ultraviolet lasers". For this reason, well made lasers have an integrated UV filter, cheap lasers emit more in the UV band and can also lack a filter. Completely apart from that however, around 75mW laser is powerful to pop a balloon or light a match quite quickly, I imagine it would take far less energy then that to do some irreparable damage to retina cells. Vespine (talk) 05:39, 22 April 2013 (UTC)

I'm thiking of infrared, not ultraviolet. It's specifically mentioned in the lede of our Laser pointer article. Vespine (talk) 06:21, 22 April 2013 (UTC)

There's some information about the mechanisms of damage (and the differences among them at various wavelengths) in Laser safety#Laser radiation hazards. DMacks (talk) 09:07, 22 April 2013 (UTC)

I am the proud owner of a (roughly) 100 watt CO₂ infra-red laser. It's a part of a laser cutter. Although it has only the power of a 100 watt lightbulb, viewing a reflection of a reflection of the laser light is enough to damage your eyesight - and it's perfectly capable of cutting through a half inch of wood...or lopping your fingers off if you got them in the way!

You might ask why 100 watts of infra-red light from a laser does so much damage when 100 watts of light from an incandescent light bulb (of which roughly 90% is infra-red) does no damage whatever.

The reason is that the light bulb distributes that light over almost 360 degrees - where the laser takes all of that energy and pushes it into a beam that (in my case) is about three hundredths of a millimeter wide. A light bulb is hot to the touch - and has a surface area of maybe 50 square centimeters...my 100 watt laser takes all of that energy and concentrates it into an area about 10²x50/0.03² = 5.5 million times smaller!

That concentration of power produces some unexpected dangers. For example, if you point my laser cutter's business end at an ice cube - it'll explode with enough violence to put dents in the steel casing of the machine! A 100 watt light bulb would probably take several minutes just to melt an ice cube - but causing the ice in the center of the cube to instantaneously flash into steam propels the resulting fragments outwards at impressive speed!

So it's not the total power of the laser that makes it dangerous - it's how concentrated it is.

The quote from Feynman is (I'm almost certain) related to him being the only person to view the very first atom bomb explosion with his naked eyes (actually - just one eye - he closed the other just in case he'd dropped a couple of zeroes in his math!)...certainly the atom bomb produced an ungodly amount of light - but the "inverse square law" meant that because the light was spreading out in all directions equally, the proportion of that light that would hit one person's retina at a distance of several miles wasn't so very much. But laser beams are a different matter. Their light doesn't spread out appreciably over very large distances - so the energy that was produced in the laser tube itself is pretty much delivered on-target with minimal reduction.

SteveBaker (talk) 15:06, 22 April 2013 (UTC)

That passage from the book has always worried me. The film of the Trinity test has a large burnt area in the centre of the negative for the first few seconds, and I'd have thought that the human retina was rather more fragile than photographic film base. I'm also not aware that the risks of looking directly at the sun are reduced in any way by plain glass, even though the UV intensity is much lower. Was Feynman just lucky that his blink reflex was fast enough - or might he have (gasp) embellished the incident? Tevildo (talk) 21:26, 22 April 2013 (UTC)

Too many variables...was the camera closer to the bomb than Feynman? What was the size of the lens focussing the light onto what size of film? What kind of film was it? The brightest part of the blast went on for too long for the blink reflex to overwhelm his desire to see the results...and it was described as being "as bright as the sun for a few seconds" - and you can certainly stare at the sun for a few seconds without damaging your eyesight. SteveBaker (talk) 23:02, 22 April 2013 (UTC)

From these: [1], [2], it appears that the eye focuses light back onto itself causing damage; from this [3], specifically "uch filters usually have a thin layer of aluminum, chromium or silver deposited on their surfaces that attenuates ultraviolet, visible, and infrared energy.", I would guess that while ultraviolet may be the most damaging, that given the intensity of the sun, it outputs enough to cause other bands to be damaging. This, [4], specifically, "Several conditions can influence the severity of the clinical and morphological presentation: intensity, duration, and light spectrum of the exposure;" would seem to indicate that the spectrum of light is a factor, so that the sun can damage beneath ultraviolet, but not as much. This, ". It is postulated that the principal mechanism of photochemical damage is from retinal irradiance by high energy wavelengths, including short wavelength-visible blue light and lower levels of UV-A or near-UV radiation (320-400nm)." from [5] seems to back that up, specifically the mention of visible blue light. While all of this is about solar retinopathy, it should apply to any light source. So, filtering out a nice % of the uv might still not be enough protection depending on the intensity, especially for sources like the sun. Unfortunately, I don't have specific numbers for any of this, nor do I have any data about the trinity events light output to say much about that.Phoenixia1177 (talk) 08:23, 23 April 2013 (UTC)

Here is my attempt to unconfuse. Feynman was referring to a time before lasers. A laser (as pointed out above) can now deliver enough energy to the retina to course permanent damage -whatever the wave length. If my memory serves my right, Feynman was standing on high ground with his colleges some 20 mile away. From that distance he conjectured that the main danger was from suffering arc eyes. Something, that in his line of work he would have been aware of . A thick pane of the right glass (not agricultural grade, not the type of glass used for sun-tan lamps and Wood's lamps, etc) is good at filtering out UV even though the brightness of the arc might leave one with temporary blindness. The danger from lasers, is that now the total amount of absorbable energy on the retina can (if it exceed so many milliwatts per square millimeter) course permeant damage. As for the cameras at the Trinity test. They needed to be near enough to have the frame filled as far possible but not so close to be blown to smithereens. The plutonium device at Trinity may also have fizzled. So some cameras were needed, that had less filtration in order to provide good diagnostic footage -had this been the case. These cameras would have certainly had their film emulsion and sub-straight damaged (burnt) by the high energy flux. Obviously, since we have good images of the Trinity Test fire-ball, some cameras were correctly filtered (calibrated) to capture the event from beginning to end. So, in other words: By trying to combine Feynman statements and lasers is to try and construct an augment based on different premises.Aspro (talk) 18:33, 23 April 2013 (UTC)

"Mozart effect" and new vs familiar music

Do any of the benefits of music described at Mozart effect last longer if new music is introduced periodically, rather than using the same music for the length of the study? NeonMerlin 06:35, 22 April 2013 (UTC)

Definition of God

I have posted what I thought might be an interesting hypothesis, that is providing reasoning for Existence of God via observation that we didn't encounter extra-terrestrial lifeforms. Due to theory of probabilities it's infinitely like that we should be surrounded by them and I have postulated, that perhaps we are not because God wants it this way. Or otherwise, if there would be no God we should have been surrounded by them. I'm interested in being mentioned of any reliable sources that argue these ideas for the purpose of inclusion on the article Existence of God.

From the criticism that my post have received, I realized that two points must be debated first. The first is, definition of God. Because really, how can be prove God exists or not if we haven't clearly defined what do we mean by God?

My own definition is quite interesting. I call it deviation from what should have been would He not exist. I'm also interested of anyone aware of such definition of God 'by effect'. Ryanspir (talk) 08:17, 22 April 2013 (UTC)

We seem to be getting a lot of these lately. This is the Science Reference Desk. It is specifically for posting questions about aspects of science that you do not understand. It is not a discussion forum. Go away. Wickwack 58.170.167.19 (talk) 09:40, 22 April 2013 (UTC)

Who are 'we'? This is a discussion about using science in the Existence of God article. 'Go away' - I would suggest you to AGF. Ryanspir (talk) 10:08, 22 April 2013 (UTC)

The Science Desk is NOT a discussion forum. If you want a discussion, fine, but don't do it here. If you want to discuss an article, use the article talk page - that is what the talk page is for. The Science Desk is not. — Preceding unsigned comment added by 144.137.226.17 (talk) 10:53, 22 April 2013 (UTC)

Ryanspir - Your use of a capital G on God implies that you are looking for the Christian god in particular, because we normally don't capitalise words that aren't proper names, or that come after the first word in our headings. If that's the case, you're prejudging this a lot and not being scientific at all. This really isn't a topic for the Science Desk. HiLo48 (talk) 10:50, 22 April 2013 (UTC)

"I call it deviation from what should have been would He not exist" How do you know what should have been would "He" not exist? What effect does "He" have? At the moment we only have one universe to look at, so I don't think we can anwser what should of been if "God" does/does not exist. If you can come up with something that's testable then come back. Absence of contact with alien life can be anwered with out the need of "God" (i.e. speed of light is the comuincation speed limit of the universe and we have only been able to detect signals for the last 60 or so years. Our galaxy is 120,000 light years in diamiter. so not decisive evidence. But to ansew your question it sounds a lot like God of the gaps. Dja1979 (talk) 14:16, 22 April 2013 (UTC)

Speed of communication and speed of traveling is not relevant if we are assuming that our time-space continuum is eternal. They would have had eternity to reach us. Imho, it's not a proving God by absence of scientific explanation. It's rather using deduction and logic while comparing to what we are observing. Ryanspir (talk) 11:40, 23 April 2013 (UTC)

No - that's the error you made before (and I called you on it). The speed of communication/travel is highly relavent if civilisations have finite lifespans...which they must because the energy of stars is not eternal. Societies may well die before they gain the technology to communicate (much less travel) over interstellar distances. You might be right - but you're seeking proof...and that you don't have unless you can somehow prove that alien civilisations last forever. I'd say that one the basis of our civilisation, it's highly unlikely that an "average" alien race would last long enough to communicate over interstellar distances.

The other thing you're conveniently ignoring is that even in an infinite universe with an infinite number of alien races within it - the distances between them can still be infinite. The density of alien races would be the number of races divided by the volume they occupy. That's infinity divided by infinity - which is an indeterminate number that can approach zero. When the density of alien races approaches zero, the distance between them becomes infinite and no communication is possible, no matter how long the universe exists.

This argument of yours is demonstrably false - just on the basis of very simple mathematics.

SteveBaker (talk) 16:33, 23 April 2013 (UTC)

We can't answer the theological aspects, but certainly we can come up with non-divine explanations for the absence of alien life. We have no current knowledge of how hard it is to make life from scratch by random chemical fluctuation! We also have no sociological knowledge of whether it is possible for a technically advanced species to avoid self annihilation. Since non-divine explanations exist, this is not a proof of existence of God. Wnt (talk) 14:44, 22 April 2013 (UTC)

That's why I was considering the hypothesis that our time-continuum is infinite and eternal as proposed in the section about it. Assuming it is, even the smallest possible chance, over infinite number of stars and planets would produce infinite number of life-forms for eternity. We would assume that from the infinite number of lifeforms, there would still infinite number of them even if very large number would self annihilated. It's mathematics: infinity - very large number = infinity. Ryanspir (talk) 11:40, 23 April 2013 (UTC)

Your math is flawed *AGAIN*. With an infinite number of life-forms, then if the probability of any given life-form "self annihilating" is anything other than zero - then the number of them that actually do self-annihilate is infinite. infinity minus infinity could be anything from zero to infinity of them left afterwards! So your argument is incorrect. You really, REALLY don't understand the arithmetic of infinities - so you're in a terrible position to be using this kind of argument to prove anything whatever. Worse still, you are still carefully ignoring my point that in an infinite universe with infinite beings within it, the average density (and therefore the average distance they'd have to travel to reach us) can be anywhere between zero and infinity...so even though there could be an infinite number of them, they could still be infinitely far apart because the universe would have to be infinite in order to accomodate them. Ignoring strong counter-arguments does not reinforce your position! Your thinking is just plain broken...you are demonstrably incorrect - and now you need to give it up! SteveBaker (talk) 19:20, 24 April 2013 (UTC)

Our OP's "definition" of god is...um...interesting? "My own definition is quite interesting. I call it deviation from what should have been would He not exist." By this definition, I am a god. Things would be different than they would have been had I not existed...of course, my dog is also a god under that definition, so I don't feel particularly special in this regard!

I mean similar to dark matter. Noone has seen it, but the science accepted it's existence because of the effects it produces. Your and your dog's influence are natural and explainable. When I say: "deviation from.." I mean that when something would happen that couldn't happen would there be no God. Ryanspir (talk) 11:40, 23 April 2013 (UTC)

That's a tough stance. As soon as something (like dark matter) appears from experimental data or other observations, science adapts it's theories to accommodate that. This happens all the time and is not considered to be remarkable. Your god then has to be able to produce effects that are outside of the realms of the laws of physics - which is (essentially) my definition that gods have to be omnipotent. SteveBaker (talk) 19:20, 24 April 2013 (UTC)

The definition I would use - because it encompasses the single biggest problem here - is something like "A being with literally unlimited powers" - omnipotence. That is the single defining thing that all claims for gods seem to share. Gods are allowed to break the laws of physics - and that's what distinguishes the concept of godhood from a supremely powerful alien or a technologically superior human (for example). SteveBaker (talk) 16:06, 22 April 2013 (UTC)

This is religious definition mostly. I don't have a strong position about omnipotence either way, though I'm likely to agree that it could have been this way. I see God more as being "inside of everything". Something like some fabric that interconnects everything there is, rather than some external entity. In that way he would be different even from the most supremely powerful aliens.

I think, before we are tying to find out His attributes, we may just first try to establish if He exists, looking at this in a scientific, non-religious way. If He has some influence, this influence can be detected, isn't it? If currently our science cannot do so, it doesn't mean it forever won't. In any case, we have somewhat intelligent minds and we can discover something even without seeing it, but by using logic and deduction.

Example: I toss a coin one million times and without any tricks the coin always falls on the same side. That is way beyond expected probability and such probability can be expressed mathematically. We may consider such occurrence as unnatural and deduct that there is some force that influences the situation, because wouldn't be there such a force, it wouldn't happen like that. Ryanspir (talk) 11:40, 23 April 2013 (UTC)

The difficulty here is that you're asking whether it is possible to prove the existence of gods if they choose to do something detectable. Obviously, if the sky were to split open, a host of angels to pour out, then this huge golden face with obligatory beard were to peer out and in deep tones say "I am your god"...then we'd have proof of the existence of god. However, nothing of the sort has ever happened, nothing that we cannot yet explain seems to require a god to make them possible. It could be that one day, all of the cosmologists peer at something that shows up on the Hubble space telescope and say "Huh! Whattayaknow? There really is a god!"...but that hasn't happened...and doesn't seem likely to happen. Some religions (I believe christianity is one of them) say that their god wouldn't let such clear proof happen because that would remove the need for people to have faith.

So this "proof" is something that might happen - but has not yet happened - and in some versions of religion, is not expected to happen.

The opposite (the disproof of god) is even tougher. If you accept my definition of omnipotence (which is definitely what it claimed for the christian god - and almost all others) - then we can never, even in principle disprove the existence of god. Suppose we were to devise some really cunning "proof" that says that there is definitely no god...well, if god is omnipotent and wishes to remain hidden, then he can just snap his fingers and magically the experiment comes out the other way and we remain ignorant. So disproof is impossible - to put it another way: "The god hypothesis is unfalsifiable".

Flipping a fair coin a million times and getting a head each time is no proof of anything. It's astronomically unlikely that this could happen by chance - but it's not impossible...and it's just as likely as getting any other outcome from a million flips. If I flip a million times, write down the random-looking list of a million H's and T's - then the probability of that exact sequence happening is EXACTLY the same as getting a million heads. Most people find that hard to understand - but it's absolutely true. Sure, we'd suspect that something was wrong - but it's not proof. Personally, I'd rate the odds of a million coin flips all coming up heads to be more likely than the existence of any specific view of what "God" is. The probability of all of those heads is very small - but the number of possible unfalsifiable hypotheses is vastly larger - so the chance that one particular unfalsifiable hypothesis is true is vanishingly smaller than a million coin flips...unimaginably smaller actually.

I think your quest to prove that something exists without first deciding (even approximately) what the definition of that thing is - is utterly pointless. If I'm looking for a Unicorn in Africa and I fail to define adequately what a Unicorn is, then I will inevitably find a Zebra and claim success! You absolutely need to know something about what you're looking for before you start a search - at least if you're expecting to come up with an answer that's logically, mathematically or scientifically reasonable.

If you claim that god is some vague "interconnectedness of all things" then maybe you'll end up worshipping the Higgs Boson.

SteveBaker (talk) 16:01, 23 April 2013 (UTC)

It's great to have you back, Steve. -- Scray (talk) 01:09, 24 April 2013 (UTC)

Lol (about worshipping Higgs Boson).

For me, practically, if I would observe an event in which constantly it's all heads for million times, without tricks, I would sign that I absolutely believe in God that very moment. However, a million is just a number. Perhaps some real hard unbeliever would need more than that. Perhaps a google or infinite would be enough?

In any case, this section is about definition of God, and if possible as scientific as possible. I have proposed my definition: That God is a deviation from what otherwise would be natural. It's an intelligent chaos that breaks otherwise predeterminated life.

I would also encourage if someone wants to say something, but it's not connected to science, please do so on my talk page. If however anyone knows any reliable sources that express ideas similar to mine - please do it here if they are of scientific nature or on my talk page. Ryanspir (talk) 17:34, 24 April 2013 (UTC)

A booming voice from the sky may simply mean one is nuts or, more sophisticatedly, that aliens such as those of a Vogon are amongst us and are there to destroy us perhaps, thus, in terms of a divinity, proves very little. Also, although its true that a string of heads is as likely as any other string, the odds of any one very long string that was selected in advance occurring with a single trial is remote. There are tests for statistical randomness and it generally takes numerous simultaneous or repeated trials of a particular string length to beat the slim odds of a particular string. Almost 1000000! two to the millionth power monkeys and coins are needed, or one monkey flipping 1000000! that many times before a match is likely. Absent anywhere near that many trials, the coin would be suspect. -Modocc (talk) 18:20, 24 April 2013 (UTC)

The idea of a million consecutive heads convincing you that there is a god is kinda silly. There are any number of ways that this could happen without divine intervention. Suppose some advanced race of aliens (or indeed, some fancy research lab right here on earth) has developed nanotechnological quadrocopter robots - each smaller than a bacterium - that are capable of pushing against a tumbling coin in flight to make it come up heads on-demand. Sure, we don't know how to make such devices right now - but they are certainly allowed by the laws of physics - and it does seem feasible that we could make them in the future. So seeing a string of a million heads might well cause a lot of scientific effort to be expended to track down the cause - but it's most certainly not a proof that god exists. I merely says that someone, somewhere has better at technology than we do and wished to mess with our heads.

(Incidentally, with a truly random coin and no external intervention, even a million monkeys with a million coins each would be unlikely to produce a million consecutive heads. The odds of a million heads is 2^1,000,000:1 against. If a million monkeys (let's say 2²⁰ monkeys) were tossing one coin each, once a second - you might still have to wait 2^999,980 seconds to see a million consecutive heads...and if each monkey flips a million coins a second, you're still only down to 2^999,960 seconds. The universe has only existed for about 2⁵⁰ seconds...so you'd need to wait through 2^999,910 universes to see this happen!) SteveBaker (talk) 19:06, 24 April 2013 (UTC)

After an edit conflict I corrected my mistake (its been a while since I figured odds and I confused the correct one with another statistic I learned which is a combinatorial factorial which happened to be vastly larger than the number needed). No one has that many monkeys or time, but the universe is vast though. After just a few flips the coin would fail the tests for fairness that I mentioned. It could still be fair, but if not, then aliens, a god (and seen as another miracle by believers) or more likely, some unaccounted for forces or masses are at play. --Modocc (talk) 19:14, 24 April 2013 (UTC)

Perhaps the closest theological definition of God that I'm aware of that fits Ryanspir's notion of God's presence is panentheism which was a reaction to pantheism, the view that the material universe itself is God. I'll add that if the size of the universe is infinite, then there just might be an infinite number of monkeys surrounding us (not that it matters). -Modocc (talk) 18:20, 24 April 2013 (UTC)

Infinite and eternal universe

I found this topic to be the most intensive. We have generally three different entities we may call universes:

1. Our universe after Big Bang. It has started from the moment of the explosion, thus not eternal. It may expand forever thus becoming eternal and infinite in space; it may remain forever in some equilibrium thus be infinite in time and finite in space; it may collapse back to a singular point, thus be finite in both time and space.

2.The very same our universe, but we are not stopping to look back at Big Bang as the point of creation. We pass this point and look beyond. What was before the singular point? There could have been another Big Bang prior to our Big Bang, after which the universe has collapsed to a singular point from which our Bing Bang originated. Or there could have been any other events that lead to the creating of singular point and the Big Bang.

I wonder why people think about our universe as that that has started after Big Bang and ignoring what we can deduct by logic. We all know for example that energy doesn't disappear, it changes states. We all know, that even if someone will say that nothing was prior to Big Bang, nothing is something. From this position, what I'm saying is: There is no such universe as that mentioned in 1).

What is mentioned in 1) is the current form of our universe. Of course the Big Bang might have redefined consonants and re-structured everything. But it's still the same energy that existed before that got restructured by the Big Bang.

Once you look beyond Big Bang(s) you can see that the universe is infinite in space and eternal. Lets use some logic deduction. How something can come out of nothing? What possible natural process could have started something out of nothing? Like, there was nothing and then something has happened and we have a universe that is not eternal back in time. And, what would be 'nothing' in that case if not also 'something'? To me, this process of deduction leads to understanding that our universe is eternal.

And about infinite space, how do you imagine the 'end' of the universe? What would be beyond that end? Some have proposed that universe somehow "circles" into itself, but still, what would be outside of that "circling"? Though it's very difficult to my human brain to understand how the universe can be infinite, it is even more difficult for me to understand how it could be finite, considering what would be beyond the finite edge?

3. Just in case some people wouldn't agree with my definitions of universe, I proposed to call "collective everything" as meta-universe, or multiverse. But in fact, meta-universe and multiverse are the same as 2) per my definition. At the same time, there are other definitions of multiverse that I do not imply, and for this reason, if 2) is not so clear, I would rather settle on to call it Time-Space continuum. In any case, those are definitions which people can use in this or other way, and it's not the definition which is important to me. So I'll repeat, by saying Universe, Meta-universe, Multiverse and Time-Continuum I mean one thing - Collective Everything. I hope I have expressed myself clear enough this time. And, I'm hypothesising that it is eternal and infinite.

Interesting, would there editors who would agree, not with that the universe is eternal and infinite, but with that the universe could have been eternal and infinite. And, if they could comment as on the likelihood in their opinion of the universe being eternal and infinite.

I'm interested to know whether there are any reliable sources that use reasoning similar to mine. Ryanspir (talk) 08:59, 22 April 2013 (UTC)

Scientists do speculate about all these things, but it is all purely speculation. We currently have no way of probing outside our universe or beyond the Big Bang, and our laws of physics don't even work at the moment of the big bang anyway. So all we have is speculation that cannot be disproved by observation. You may be interested in Big_bang#Speculative_physics_beyond_Big_Bang_theory and multiverse. Someguy1221 (talk) 09:41, 22 April 2013 (UTC)

That's right, scientists speculate about this. That's why I was wondering why almost every editor declined possibility of infinite and eternal universe on my original post. I understood it's because of the definitions I have used, so I wrote in a more precise and clear way what I mean. Ryanspir (talk) 10:12, 22 April 2013 (UTC)

Ryanspir, don't bring your wierdo faith theories here. This desk is for asking science questions. Your pontifications will drive away folk who want a science question answered, and you will discourage folk with science knowlege from looking here to see if there is a question they would like to answer. — Preceding unsigned comment added by 144.137.226.17 (talk) 10:57, 22 April 2013 (UTC)

We don't know what happened at the Big Bang. The Big Bang is not an explosion; it is a singularity in the equations where known physics breaks down. Therefore, we can't say whether the universe existed before 13.8 billion years ago.

We also don't know whether the universe is infinite. There's just no evidence either way. That's not an excuse to make things up and believe in them; it's an excuse to keep investigating to push out the boundaries of knowledge. History shows that whenever anyone makes a statement without evidence, whether in the name of religion or philosophy, it will be wrong. Humans are simply incapable of guessing correctly about the universe without the harsh light of empirical evidence. --140.180.244.177 (talk) 11:06, 22 April 2013 (UTC)

Ryanspir (talk · contribs) is being talked about at Wikipedia talk:Reference desk. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:05, 22 April 2013 (UTC)

What is clear is that there is no evidence that time exists. I.e. for all we know, the present moment doesn't single what is real and what is not (yet or anymore). It's simply that we are located at some moment and the other moments have equal existence. This is the block time view, which is consistent with all of modern physics. Then, it doesn't make sense to consider the end of the universe as some final end to everything, because even if it where to end in the future, we would still find ourselves editing Wikipedia well before the end of the universe. Count Iblis (talk) 14:26, 22 April 2013 (UTC)

• I think that "time" as we measure it may not be the only way of looking at it, or even the most important. A second is defined as so many vibrations of a cesium atom, but what was a second in a universe smaller than a cesium atom, full of inconceivably hot substance? The smaller the universe, the more things crash together in a unit time - if we think of each collision as a "happening" then stuff "happened" at an asymptotically rapid rate as you look toward the beginning. The result is that whole epochs of changing physics with the most far-reaching effects on our modern cosmos happened in what seem like absurdly short periods of time. Therefore, I would suggest an answer for your third question by saying that our measure of time doesn't go before the Big Bang because it is a purely mathematical singularity - the visible horizon of an infinite sky, so to speak. And your first question's answer therefore would be that the universe remains unbounded in terms of the number of "happenings" at its beginning and at its end, regardless of whether either was once a mathematical singularity at a known time. Wnt (talk) 14:39, 22 April 2013 (UTC)

There are plenty of ways out of the "What happened before the Big Bang?" trap. I particularly like the one that Hawkins proposes in "A Brief History of Time" which is that time is compressed in the early universe - just like space is. As you head back in time towards the big bang, time gets more and more compressed - until at the instant of the big bang, time is passing infinitely slowly. This permits a universe that has been here for infinite time, while still only being recognizably like our modern universe for a clear, finite amount of time. Another possibility is that our universe will end in a "Big Crunch" or a "Big Rip" - either of which could be the immediate cause of a new universe being formed with a Big Bang from the remnants of ours...this would produce a cyclic behavior that would mean that these series of universes go back into an infinite time. Even more odd is the idea that every big bang is exactly the same - so each new universe is utterly identical to the one it was born from...so, in effect, time is a finite closed loop.

We don't know which (if any) of these explanations is true - but the lack of a "known true" explanation is not sufficient to "prove" the existence of gods.

Our OP also needs to know that the "tactic" of continually asking "Well what came before that then?" will backfire very badly on anyone claiming that a god or gods is the answer. Science's first response to the the idea of the literal existence of a god is "So what caused God to exist then?". Religious people will proudly answer either that their particular god has always been there or that time is meaningless for god...totally failing to see that this is precisely what science says about the universe at the moment of the big bang! So it is inconsistent to claim that god is the answer to the ultimate cause of everything and that he has no cause - and yet deny that the big bang could be the literal start of all things for the exact same reason!

SteveBaker (talk) 15:58, 22 April 2013 (UTC)

Actually, science doesn't say that the universe had always been there at the moment of the Big Bang; it says that we simply don't know what happened, just as we don't know what happens at the singularity of a black hole. That's the only honest answer. The religious alternative--to make stuff up and claim evidence isn't necessary--is a dishonest God of the gaps fallacy. --140.180.244.177 (talk) 17:05, 22 April 2013 (UTC)

It's certainly true that we don't know (with scientific rigor) what happened that far back. However, in an effort to prove the existence of god or gods - all we need is to say that science doesn't rule out the idea of finite time or infinite time. That means that our OP cannot say "Because time is infinite..." and deduce anything from that. Sure, we don't know that time is finite - but we also don't know that it's infinite...so you just can't base a "proof" around a gap in knowledge. All that is required to demolish this so-called proof is that it's not scientifically implausible for the Big Bang to be the literal start of everything. SteveBaker (talk) 19:22, 22 April 2013 (UTC)

Steve, this is not about the OP's question, but I don't understand your previous comment about time passing slowly at the beginning of big bang. According to Hawking, time had beginning at the big band, and AFAIK each of the 13.7 billion years of age of universe is same as a year on earth now. When we say supernova explosion occurred say 10 billion years ago, we say it happened at 20 billion light years away (due to expansion), but we never say when big bang happened 13.7 billion years back, it actually happened many more billion years back (because time was much slower earlier than current year). manya (talk) 04:02, 23 April 2013 (UTC)

Hawking's "no-boundary proposal" about the beginning of time, which he talked about in A Brief History of Time, was never widely believed and isn't a part of modern cosmology.

The 13.7 billion years are years of 365.25 × 24 × 3600 seconds each, and a second is the same all the way back. I don't think Hawking ever suggested otherwise. The nature of time has been essentially the same since the big bang, as far as anyone can tell.

In modern cosmology the big bang is just the end of the inflationary epoch, the length of which is unknown but could be very large or infinite. So modern cosmology has nothing to say about the beginning of time. -- BenRG 05:44, 23 April 2013 (UTC)

Seconds were defined the same way, sure ... but where was there a grandfather clock to measure them when the universe was the size of a cesium atom? No doubt you could work out some kind of conversion from an event of the type that could have been observed then, but on that timescale a second would be such an incredibly large period of time as to have no relevance. Moving at nearly the speed of light something could bounce off or otherwise interact with "practically every particle in the universe" (well, not really, but some vast number) in that time.

Now the big difference between such a universe and ours really is that every particle we know of would be going at practically the speed of light. Only if there were some particles so incredibly supermassive that they could actually move slowly could there have been little teeny-weeny "planets" or "galaxies" or "people" or some such thing that would stay together. At least, I think ... though I wonder if I've missed some of the relativistic perspective. Anyway, I don't think anyone has come out and said plainly that now that the Higgs is known, there can be no more particles discovered no matter how much power we dump into a supercollider ... have they? Wnt (talk) 21:57, 23 April 2013 (UTC)

Electomagnetic fields to purify water?

Can someone explain to me in simple terms how pulsed-power water treatment works? It seems like pseudoscience marketing bullshit to me - something like using magnetic fields to improve your gas mileage or make you a better athlete. Deli nk (talk) 15:31, 22 April 2013 (UTC)

There is a method to rip bacteria apart by pulsing an electric field (not electromagnetic). But the article (pulsed-power water treatment) seems to lack any sufficient scientific explanation of the procedure to evaluate its merits. The article does in fact look like an advertisment in disguise. It ought to be cleaned up and explained in terms of volt, current, time, electrode placement, biomechanism etc. Electron9 (talk) 15:37, 22 April 2013 (UTC)

As far as I can tell this is legitimate. It isn't supposed to purify water, only to kill bacteria and reduce sedimentation. The idea is to apply brief pulses of very high voltage -- high enough to disrupt the cell membranes of bacteria or other organisms. There is some scientific literature on the technique, although not a lot. Looie496 (talk) 21:41, 22 April 2013 (UTC)

..and of course there are plenty of things apart from bacteria that can contaminate your water. Richard Avery (talk) 07:05, 23 April 2013 (UTC)

Well, the sources in our article all look fairly iffy - white papers and industry institute publications. I don't think one of them was published in a properly peer-reviewed journal. --Stephan Schulz (talk) 14:44, 23 April 2013 (UTC)

This PDF has some technical detail, although it's written by people who don't know the difference between an electric field and a magnetic field. According to this article, pulsed power involves a solenoid wrapped around a plastic pipe. The amount of power it consumes is suspiciously small (2.4 kVA for a 12 inch pipe). There may also be electrostatic methods but I couldn't find any that were in commercial use. --Heron (talk) 21:01, 23 April 2013 (UTC)

Note that for all the problems with our article, it does seem to emphasise it's for cooling towers and similar things, in other words as Looie496 suggested, no one is suggesting using it to produce potable water. (There is some mention of using it to treat fruit juices, but with much higher energy levels. Of course the requirements there are also quite different.) Nil Einne (talk) 03:18, 24 April 2013 (UTC)

I shared a lab with somebody once who was looking at this, with particular reference to preventing scaling of pipes. The device was basically just a current carrying wire that was wrapped around the copper water-carrying pipe. It was advertised in the Sunday supplements, and the manufacturers wanted to know how it worked. Much to our suprise he concluded that it did reduce descaling, which appeared to be by altering the crystallline polymorph of the calcium carbonate formed to one that was slightly less prone to sticking together and thus more prone to being flushed through the system. We never quite worked out how this occurred though; it seemed to be that there was a small vibration which caused seed crystals of the desired polymorph to form, and once this was underway further precipitate stayed as that polymorph. Chris (talk) 21:57, 24 April 2013 (UTC)

Simplest way to represent Graham's number

Is there a way more simple than arrow notation to imagine Graham's number? Is it possible to say how many times Graham's number is greater than Skewes', which according to what I read is 10^101034?

I also wonder whether it's possible via similar power tower to represent how many times G is greater than the number of atoms in observable universe for example? --93.174.25.12 (talk) 17:04, 22 April 2013 (UTC)

Wouldn't this be better asked at the Mathematics desk? --Jayron32 17:08, 22 April 2013 (UTC)

No (to OP, yes to Jayron). According to our article on Graham's number, the number of exponent towers (not their value) for the first layer of arrows is already far greater than the volume of the universe divided by the Planck volume. There are 64 layers of arrows, each unimaginably greater than the one before it. So no, it's not possible to represent Graham's number using a power tower, even if you divide it by a tiny number like 10^80 (the number of atoms in the universe) or 10^10^10^34. --140.180.244.177 (talk) 17:17, 22 April 2013 (UTC)

Thanks to you all I now have a headache wondering how you say in ordinal numbers the number that's one before Graham's number... --TammyMoet (talk) 19:23, 23 April 2013 (UTC)

"Graham's number minus first", of course. --Trovatore (talk) 21:02, 23 April 2013 (UTC)

"Graham's number minus oneth", of course. --ColinFine (talk) 16:13, 24 April 2013 (UTC)

No no no!!! (n−1)st, never ever ever (n−1)th. There is no such word as "oneth". --Trovatore (talk) 01:27, 25 April 2013 (UTC)

Would you say that expression, "En minus first"? Sounds weird. -- Jack of Oz ^[Talk] 09:19, 25 April 2013 (UTC)

Not nearly as weird as "en minus oneth". I suppose this is probably just what one is used to, but yes, I've almost always heard "en minus first" used. It's a natural extrapolation from (say) "twenty-first".

Now, in Italian, you say ventunesimo and not *ventiprimo or some such, so there I would expect enne piú unesimo, but in English there is never any "oneth". --Trovatore (talk) 17:49, 25 April 2013 (UTC)

When I was involved in Dungeons and Dragons, many, _many_, years ago, we used to distinguish "second", "first", "zeroth", "minus oneth" and "minus twoth" versions of the game. Barbaric it may be, but not an unknown usage. Tevildo (talk) 20:19, 26 April 2013 (UTC)

And the onuth ith on all of uth to remember thith. -- Jack of Oz ^[Talk] 04:51, 26 April 2013 (UTC)

Doron Zeilberger has said that Graham's number probably does not exist. Count Iblis (talk) 16:47, 24 April 2013 (UTC)

The number itself must exist - it's the idea that it's "the upper bound on the solution to a certain problem in Ramsey theory" that's in doubt. Since it's only an upper bound, it's easy to imagine a better approach to solving these problems that would come out with a smaller number for that upper bound. But without that connotation of being the largest number we've ever actually needed in practical mathematics, it's not a particularly interesting number. It's easy enough to write down yet larger numbers using the right notation - they just won't be particularly notable, and nobody is going to bother to name them. SteveBaker (talk) 18:45, 24 April 2013 (UTC)

Yes, but the supporters of ultrafinitism are arguing that beyond some point, extremely large numbers don't actually exist. The article says: "In addition, some ultrafinitists are concerned with our own physical restrictions in constructing (even finite) mathematical objects. Thus some ultrafinitists will deny the existence of, for example, the floor of the first Skewes' number, which is a huge number defined using the exponential function as exp(exp(exp(79)))". Zeilberger has made the point that when we do computations with integers then while we pretend to do computations with the countable integers, we're always using some device with a finite capacity. Then if the results are always going to be consistent, at most you can do computations modulo some large integer. Count Iblis (talk) 19:14, 24 April 2013 (UTC)

Light reflection

I have a light bulb that emit light color like this. When I hold my near-sighted glasses under the light, I saw reflections of many colors such as blue, green, purple, red, yellow and some mixed colors, similar to rainbow I think. So anyway I'm curious about how did it happen. How did one simple color turned into many different colors when it went through the glasses? I know this has to do something with physic but incapable of understanding it. Thanks!Pendragon5 (talk) 21:28, 22 April 2013 (UTC)

What you are seeing is iridescence, and it is most easily produced by thin films. Most likely your glasses have some sort of thin coating. Looie496 (talk) 21:45, 22 April 2013 (UTC)

I suppose it's also possible that your glasses are acting like a prism to separate out the colors. Light emitted from a hot surface contains a wide range of colors all mixed up together - but most transparent materials bend light by different amounts depending on the frequency of the light - and frequency determines color. So what goes into the lens as a mixture of many colors gets separated out - exactly like a rainbow. Looie's answer of "iridescence" is another possibility though - it's hard to know without seeing the effect for ourselves. SteveBaker (talk) 22:29, 22 April 2013 (UTC)

Please explain in more details. So let me see if I can get this concept correct. Since my glasses has a curvature in it so does that mean the color depends on which angle the light hit on the glasses to produce different colors? But why each angle and different location on the glasses produce different color? I kind of understand it somewhat has to do with constructive interference, so there must be some sort of mixing light waves of different colors. But how exactly the rule works? Like what angle creates what color? What thickness creates what color? I know both angle and thickness of the thin film have an effect of changing the color. But how does the combination work? Example question is what angle + what thickness = what color? (Some additional info is when you look at my near-sighted glasses, you do not see a bunch of random colors all over the places but you will see many perfectly round shape dots that have different colors. Some dots have 2 colors and mixed colors of the two in the middle of the dots). Pendragon5 (talk) 22:41, 22 April 2013 (UTC)

I've noticed for a few pairs now that my glasses have an iridescent coating; I believe it is the anti-glare coating which I purchase every time I get a new pair. Gzuckier (talk) 04:18, 23 April 2013 (UTC)

I've noticed variations in colors for lens coatings as well, and I'm not sure if it's a proprietary thing or if there are advantages to the colors. There do seem to be cost differences, if I recall correctly. So, totally original research, but I remember my glasses as a kid reflecting a purple-blue hue. My current glasses have a greenish coating on them, and I recall an expensive option was the Chrosziel coating, which was a glorious gold color—of course, looking through the glasses shouldn't have changed anything, and I assume each coating wouldn't change the a prismatic effect that much, which to me would be caused by the curvature of the lens/glass. – Kerαunoςcopia^◁_galaxies 01:20, 24 April 2013 (UTC)