Wikipedia:Reference desk/Archives/Science/2011 May 10

= May 10 =

Blackhole Theory
There are two theories that I'm aware of concerning the centre. One is a singularity, where all the information is contained with in zero volume. The other theory, is a state of matterial quantumn superposition contained within a non-zero infinitesimal volume, involving supersting theory.

In a situation where two black holes collide, how would the sequence of events differ according to each theory? Plasmic Physics (talk) 03:25, 10 May 2011 (UTC)


 * i dont know about the two situation but continuing the two theories you mention aventaly data gose out .thank —Preceding unsigned comment added by 77.127.152.95 (talk) 04:21, 10 May 2011 (UTC)


 * From an external point of view (i.e. outside the event horizons) those two scenarios are identical. Dragons flight (talk) 06:10, 10 May 2011 (UTC)

And for an internal observer? Moreover, since the second theory requires a non-zero infinitismal volume, there should be a force gradient across the centre entity of each black hole. (Conjecture) Plasmic Physics (talk) 08:21, 10 May 2011 (UTC)


 * Is this singularity really a “theory”? I don't think so.  I thoguht "singularity" is just a way to highlight the problem with this simple model of black holes.  &#x2013; b_jonas 09:06, 11 May 2011 (UTC)

OK, how would you suggest I restructure my question? Plasmic Physics (talk) 10:39, 11 May 2011 (UTC)


 * One acknowledges that something is there and the other doesn't or cant (shouldn't)?? —Preceding unsigned comment added by 98.221.254.154 (talk) 02:35, 12 May 2011 (UTC)

Ninth Planet
I know there are only 8, but for the life of me, I can't remember which planet was canned? Glitch Turner (talk) 03:42, 10 May 2011 (UTC)
 * Pluto. Dismas |(talk) 03:45, 10 May 2011 (UTC)
 * There was talk of renaming it Ham, so they could say they had canned Ham. ←Baseball Bugs What's up, Doc? carrots→ 03:46, 10 May 2011 (UTC)
 * As a side note, after its discovery, Ceres was for some period (and in some countries) [|considered a planet], as other asteroids to be later discovered. SamuelRiv (talk) 17:50, 10 May 2011 (UTC)
 * Another side note: Pluto was discovered in January 1930 - 81 years ago.  Pluto takes 248 Earth years to make one orbit of the sun.  So in all the time that we have known about Pluto, conferred planet status upon it, then removed that status, it has covered only 117 degrees of arc around the sun, one-third of an orbit, or one-third of a Pluto year.  Dolphin  ( t ) 23:15, 10 May 2011 (UTC)

LHC
what is the LARGEST SIZE black hole that (if created using a hypothetical "black hole machine" on the surface of the earth) would NOT absorb the earth and surrounding matter, but instead evaporate "harmlessly"? I did not think i had to say this but: please only answer if you know the correct answer and are willing to share it with others. thanks. I was going to say you could also say: "I don't know" but i figured then everybody would feel obliged to respond. —Preceding unsigned comment added by 98.221.254.154 (talk) 05:07, 10 May 2011 (UTC)
 * When someone else tries to answer, as Count Iblis did above, are you just going to berate that person as well? -- Jayron  32  05:10, 10 May 2011 (UTC)

No —Preceding unsigned comment added by 98.221.254.154 (talk) 05:32, 10 May 2011 (UTC)


 * The evaporation time for a blackhole is
 * $$t_\mathrm{ev} = 8.407 \, 16 \times 10^{-17} \left[\frac{M_0}{\mathrm{kg}}\right]^3 \mathrm{s}$$.
 * Hence to prevent evaporation, a black hole will need to consume roughly it's own weight in stuff for each $$t_\mathrm{ev}$$. Assuming a ambient density like that of rock, 3 g/cm3, and that nearby mass is sucked in at the speed of light (obviously false, but it puts a lower bound on the mass), would imply:


 * $$M_0 \approx {4 \over 3} \pi(3 \, \mathrm{g} / \mathrm{cm}^3)*(c*8.407 \, 16 \times 10^{-17} \left[\frac{M_0}{\mathrm{kg}}\right]^3 \mathrm{s})^3$$


 * $$ \Rightarrow M_0 \gtrsim 220 \, \mathrm{kg}$$


 * That sounds small, but there are still a lot of particles required to get to that much mass. The entire LHC beam has only 1014 protons, which amounts to only about 2 &mu;g of mass.  Also, the assumption that the black hole could eat everything in its light sphere is a wild overestimate since the force from a 200 kg black hole at even 1 mm distance is already much, much less than typical interatomic forces that hold matter together.  I've seen it quoted before that a stable micro black hole really needs a mass comparable to a mountain in order to eat enough material to counteract Hawking radiation losses.  Dragons flight (talk) 05:46, 10 May 2011 (UTC)


 * If you're asking in connection with the safety of particle collisions at the Large Hadron Collider, note that all of the LHC black hole doomsday scenarios assume that black holes do not evaporate. They also assume that the standard gravitational constant (which went into Dragons flight's formulas) is wrong, and the real constant is much larger (with the discrepancy being hidden until now by large extra dimensions). -- BenRG (talk) 08:03, 10 May 2011 (UTC)

What I'm really trying to get at is the tipping point of a black hole's mass (on earth's surface - someplace I'm familiar with,)above which it will begin to absorb all the ambient mass and below which it will not absorb the ambient mass but instead evaporate. Is there such a mass? —Preceding unsigned comment added by 165.212.189.187 (talk) 13:19, 10 May 2011 (UTC)
 * I'm not sure what more you want; the previous answer seemed quite comprehensive and gave a lower limit. It is likely much higher than this, but any more exact of an answer requires wild speculation and conjecture on the exact behavior of solid matter around a black hole. - Running On Brains (talk) 14:08, 10 May 2011 (UTC)

So is it 200 kilos or a mountain? does that mean that a 200 kg black hole on the surface of the earth will not cause damage to the earth? how quickly will it evaporate? —Preceding unsigned comment added by 165.212.189.187 (talk) 14:16, 10 May 2011 (UTC)
 * dragons flight already quoted the evaporation time for you. Dauto (talk) 14:45, 10 May 2011 (UTC)

I would estimate this as follows. The radiation pressure of the electromagnetic component of the Hawking radiation is:

P = $$\frac{\hbar c^9}{15\times 2^{14} \pi^{2} G^4 M^4}$$

Equating this to 1 bar and solving for M yields $$M = 8.1\times 10^{17}$$ kg. The Schwarzschild radius is then 2.1 nanometers. If you don't manage to keep this from sinking into the Earth, then you equate the pressure to the pressure at the Earth's center. Count Iblis (talk) 15:21, 10 May 2011 (UTC)

I should be a dentist. So is it 200 kilos or a mountain for a black hole's mass (on earth's surface - someplace I'm familiar with,)above which it will begin to absorb all the ambient mass and below which it will not absorb the ambient mass but instead evaporate. Is there such a mass?? does that mean that a 200 kg black hole on the surface of the earth will not cause damage to the earth? —Preceding unsigned comment added by 165.212.189.187 (talk) 15:38, 10 May 2011 (UTC)
 * You can prevent significant damage to the Earth, but you are doomed either way. There exists some critical mass Mc, above which the black hole will eat up the Earth. This means that if the mass less than Mc, it will evaporate. But that will then happen quite fast. A black hole of 200 kg will be converted partially to electromagnetic radiation. Try to estimate how many megatons of TNT that explosion is equivalent to. Count Iblis (talk) 15:49, 10 May 2011 (UTC)
 * FYI, it's about 220,000 times the explosive yield of the nuclear bomb dropped on Nagasaki. --Tango (talk) 22:09, 10 May 2011 (UTC)
 * The 200kg estimate was a lower bound, it could be much higher. At the level of precision of that calculation, a mountain is consistent with that estimate. --Tango (talk) 22:09, 10 May 2011 (UTC)

This all assumes the cube-square law applies to gravity at the microscopic scale, which is assumed but untested. Hcobb (talk) 22:38, 10 May 2011 (UTC)

planetesimals
please read this subject then say me about my question : Accretion of Planets {Planets formed in the Solar Nebula from the slow accretion of small dust particles (via electrostatic forces) into 1-10 km size planetesimals -Formation of the Terrestrial Planets: In 100,000 years, planetesimals up to 10 km in size would have formed. The accretion continues, but fueled by the gravitational attraction of the biggest planetesimals: The big keep getting bigger swallowing up smaller planetesimals near its orbit. The growing young planet absorbs the mass and the orbital energy of all the smaller objects, circularizing (averaging out) the final orbit. Perhaps a hundred Planetary Embryos form, with Moon masses (1/10th Earth). They interfere with each other's orbits. This mixes up the differing planet chemistries created based on distances from the Sun. More importantly, the embryos collide! This process creates the few final planets, when all embryos have been assimilated in 10 m.yrs. }Dr. Margret Hanson,  university of Cincinnati(UC)form her personal web site question :could such the planetsimals be spiral ?(consider the energy of bending early mass)--78.38.28.3 (talk) 06:22, 10 May 2011 (UTC)a. mohammadzade


 * Quite unlikely. Small enough objects can take irregular shapes, though, so it is possible, I suppose.  Larger objects are all roughly spherical, or an oblate spheroid, when deformation due to rotation is considered. StuRat (talk) 09:48, 10 May 2011 (UTC)

Children sweat less than adults?
Do (human) children sweat less than adults? I've looked at our sweating article, but it doesn't say anything about this. Do we have any articles mentioning this or the contrary? If they do sweat less, what's the purpose for this? Thanks, &#x2013; b_jonas 10:03, 10 May 2011 (UTC)


 * In absolute amounts, I'm sure they do sweat less, as less skin will produce less sweat, everything else being equal. If you mean to ask if they sweat beyond proportionally less, that I'm not sure of.  Since smaller humans will have a higher surface area to mass ratio, they will tend to cool off faster, assuming that the ambient temperature is below body temp, so they might have less of a need to sweat, then.  However, if the ambient temp is above body temperature, they might need to sweat more.  Kids under the age of puberty also seem to produce less oil in the skin, and hence don't need to bathe as often to keep from stinking.  This is distinct from sweat, though, which is primarily just salt-water. StuRat (talk) 10:25, 10 May 2011 (UTC)


 * A web search finds this article which claims that children sweat less than adults. &#x2013; b_jonas 11:48, 10 May 2011 (UTC)


 * It has been suggested that sweat had (in our distant past) a role in attracting the opposite sex. "Growth, Maturation, and Physical Activity" says "..observations in boys have shown that the increase in sweating rate starts when the child reaches early puberty. A similar trend occurs among girls, but in general, the diffferences in sweating rates related to maturity in females are less than in males." Further down it says that the reason for this increase is unclear, but may be related to the amount of energy available for sweat production. Alansplodge (talk) 12:44, 11 May 2011 (UTC)


 * Not just our distant past. There is a culture where men dance around to get good and sweaty, with cloths under their armpits, then present the smelly cloth to their intended.  It seems odd that one culture can find something sexually attractive which others find repulsive. StuRat (talk) 17:52, 13 May 2011 (UTC)

The scale of temperature in water
Compare a glass of cold water with a glass of warm water. The difference between them will be that the water molecules will have a faster movement among themselves - is this the physical explanation of the temperature? Then: 1) can a single water molecule have temperature? 2) what about if one puts a finger in a water bottle and shake it, you will feel the water will move around randomly, but you will not feel an increase in its temperature - at what scale does water go from simple water movement/current to a change in temperature? —Preceding unsigned comment added by 83.226.142.75 (talk) 11:06, 10 May 2011 (UTC)


 * The fact that you can't feel an increase in temperature when you shake the water is due to the poor sensitivity of your finger to temperature change. You just need a more sensitive instrument to measure such a small change. Roger (talk) 11:39, 10 May 2011 (UTC)


 * Yes our skin isn't sensitive enough to detect the temperature change due to minor shaking, but you could add more energy to the water. If you put room temperature water in a high-power Agitator_(device), you could feel the increase in temperature. SemanticMantis (talk) 13:33, 10 May 2011 (UTC)


 * We actually have an article on the mechanical equivalent of heat, which involves the direct measurement of the heat produced by mechanical agitation of a liquid (usually water). It's a fairly common introductory physics/calorimetry demo. TenOfAllTrades(talk) 18:19, 10 May 2011 (UTC)


 * I don't think the question is regarding the extra energy that the shaking finger adds to the water (where I agree you're correct) but rather this: if water feels a given temperature because its molecules move at speed X, and I move my finger around at speed Y, why don't I feel a temperature corresponding to molecules moving at speed X+Y? I'm near certain that you won't observe this if you shake a highly-accurate digital thermometer in a glass of water, either, so obviously temperature doesn't work exactly like this highly abstracted example. Perhaps it's because that for every molecule hitting at X+Y speed there's also one hitting at X-Y speed, perhaps because molecular motion X is just orders of magnitude larger than finger motion Y, I don't know -- but I don't think "poor sensitivity" is the answer to what's being asked (note that "shaking the water enough to add significant heat via friction" is a different scenario and is covered above). &mdash; Lomn 16:09, 10 May 2011 (UTC)


 * Quoted from temperature: "The thermal motions of atoms are very fast and temperatures close to absolute zero are required to directly observe them." Unless you can move your finger so fast that it is impossible to observe your finger's motion, the energy added by wiggling your finger around is negligible compared to the energy already in the liquid. -- k a i n a w &trade; 16:45, 10 May 2011 (UTC)


 * However, note that the viscosity of water or any fluid (not super) will create friction on shaking which will raise the temperature enough so that you will eventually feel it. It's a much much larger effect than the movement of molecules on which the shaking itself would have zero effect on the total temperature (since temperature is a statistical quantity and the molecules are moving in sync). I'm not sure if my calculation is correct (looking up an engineering calculator for an equation with which I am entirely unfamiliar), but it seems that you can produce quite a large temperature change by shaking, on the order of 1K per minute! (that is, raising the temperature of the water by 1 degree celsius per minute of shaking.) SamuelRiv (talk) 18:04, 10 May 2011 (UTC)


 * The temperature is a huge number of small, seemingly random, movements, which average out to zero. If the molecules were all moving the same direction, the water would then move very fast, and you could appreciate how the tiny movement you add is insignificant by comparison. StuRat (talk) 18:51, 10 May 2011 (UTC)


 * See Boltzmann constant. The motions of the particles of a gas at room temperature are measured in hundreds of meters per second.  Wiggling just isn't enough to matter.  But if you bring a rocket ship through the air at such a speed or faster, it certainly heats up. Wnt (talk) 21:20, 10 May 2011 (UTC)

Strength of steel for making a table
Hi all,

I'm building a table, and I'd to double-check my math before I make something that falls apart in the wind.

Long story short: I'm wondering whether using rectangular tubes 3"x1.5" of 11 ga will be strong enough for the frame 5' in length.

I want to create a very simple frame which will support a tile top. It will be a simple rectangle with four legs. The top will be 5' x 2.5'. If I understand right, the main thing I should be checking is that I won't have any deflection along the length of the table, the 5' beam. I think the whole table should be able to carry about 600 lbs, so let's pretend that's 300 lbs per beam directly at the center. (Reasonable assumption?)

I want to use 3"x1.5" rectangular tubes of mild steel.

If I understand this site right, a 3"x1.5" 11ga steel tube (0.12" thickness) should have a Moment of Inertia of 1.17.

If I understand this site right, a 5' steel beam, with 300 lbs at 2.5', with an I of 1.17, should deflect no more than 0.02", which seems very reasonable to me. (I don't know if this is actually reasonable, being a metal-working newbie.)

Does that seem about right? Wall thickness of just 0.12" sounds very small and light to me, but I guess maybe I'd probably be surprised at how strong it is?

Any help much appreciated! &mdash; Sam 63.138.152.219 (talk) 13:43, 10 May 2011 (UTC)


 * In my opinion you should (1) build it to hold at least three times what you expect it to actually hold, and (2) build it so that it won't collapse if all the weight is on one support. Overbuilding is always better than underbuilding. Looie496 (talk) 16:57, 10 May 2011 (UTC)


 * Well, playing around with the site more, it looks like the deflection increases linearly with the weight (at least at the beginning). Doubling the weight to 600 lbs per side still gives a deflection of just 0.04 inches. This still seems like it should be fine to me, especially as I'm never going to have 1200 lbs directly at the center.
 * What I still don't know, though, is
 * Am I even doing the right calculation? Is there a different calculation I should be performing to see if my table will hold the weight?
 * Do all these values seem reasonable? As far as I can tell, the site isn't using SI units, so maybe it's telling me it will deflect 0.04 feet instead of inches... They just seem to assume everyone knows what units to use...
 * Is 0.04" actually a reasonable deflection, or will the table seem flimsy?
 * I guess most of the problem is that I haven't used 11 ga steel tubes before, so don't know how sturdy they are. If I had a steel shop near me, I could probably find this out much easier, but I don't. &mdash; Sam 63.138.152.135 (talk) 19:15, 10 May 2011 (UTC)
 * One thing to keep in mind regarding point 3 and 'flimsiness': those deflection calculations are based on an assumption of perfect anchoring at the end of the beam, which a real table will not have. Surely your legs will be strong enough in an idealized sense of bearing a static load directly perpendicular to the surface, but in real-life all kinds of shear stress come into play. You have to worry about overall structural integrity and stability under a variety of forces, not just a 'clean' loading. In short, tables feel very flimsy if not braced properly, regardless of the material strength of the members. (You probably know this, but I just wanted to point out what the calculations are not taking into account.) SemanticMantis (talk) 19:57, 10 May 2011 (UTC)
 * That's a good point. I'm going to be TIG-welding the frame and the legs together, much like this, so it should be pretty strong -- much stronger that those flimsy table legs held on by diagonal screws, at least. But it's another point that I should over-engineer, as you say. &mdash; Sam 166.186.168.64 (talk) 21:38, 10 May 2011 (UTC)

Ethnic-specific biological weapons
I read that apartheid South Africa allegedly researched the idea of a biological weapon that would only kill blacks (ugh!). Propaganda (probably false) has circulated for years about supposed Israeli research into an "ethnic bullet" that would only kill arabs. My question is, has anyone shown the potential to make such a concept into a reality, at least in theory?

I'm aware that some groups, having not been exposed to a given disease, may lack immunity which other groups have developed with exposure. The Australian Abroginies were devastated by diseases brought by white settlers in precisely such a fashion. But as far as genetics itself goes, has anyone shown even a proof-of-concept success in producing an ethnic-specific biological weapon? From what we know today, could it theoretically be done?

Do excuse the gruesomeness of this question - it's merely an academic interest of mine. I have no intention of developing bioweapons. 124.179.224.106 (talk) 19:43, 10 May 2011 (UTC)


 * Considering the only real difference (socioeconomic issues aside) between races is melanin, I feel safe saying that it would be impossible; and as a person with a BS in Physics, I do not use that word lightly. This is of course ignoring the fact that the term "race" is not universally defined, and ignorant people will often lump culturally and genetically different people together as the same "race".- Running On Brains (talk) 20:52, 10 May 2011 (UTC)


 * There are many differences besides melanin between ethnic groups, such as hair texture, eye color, and inherited diseases like Tay-Sachs and sickle cell anemia. I can see developing a disease that would wipe out people with a single sickle-cell gene, for example.  That wouldn't target one race 100% and always miss the other, but it certainly would be better than germ warfare that affects everyone equally. StuRat (talk) 21:16, 10 May 2011 (UTC)


 * I guess I was misunderstanding the question. The answer I was trying to convey is: if you're looking for a weapon which will only affect members of one race, that is impossible. Sickle-cell anemia is not just a "Black person" disease, and it affects white people too, granted to a much lower extent. - Running On Brains (talk) 21:24, 10 May 2011 (UTC)


 * It seems possible to me. Of course, more widely divergent ethnic groups, like white South Africans of Dutch and English descent versus blacks of native descent, are more likely to have genetic differences which could be used to develop such a weapon.  Palestinians and Israelis, on the other hand, both being Semetic, are more similar genetically. StuRat (talk) 21:08, 10 May 2011 (UTC)


 * As a rule, there is no single gene that you can point at and say that a form of it uniquely labels everyone of one race and no others. However, in a small environment with two fairly distantly related races, you might come up with a gene that works within that small region.  For example, a small village of German-descended Brazilians might, by chance, have a high frequency of blood type B; the Brazilians might then attack them with toxoplasmosis based on the possible increased vulnerability of people with that blood type.  Overall in the world, however, as illustrated in race (classification of human beings), a war on the B blood type would be a very blunt instrument indeed.  Now races can be defined in terms of clusters of genes, whose effect can be measured phenotypically (see Lewontin's Fallacy)  So if you wanted to make a war on blacks, you might devise some intestinal bacterium that secretes an enzyme to destroy dietary vitamin D, or if you wanted to make a war on whites, by a virus that directs production of a phototoxin.  In this way you wouldn't need to find one form of one gene, but could average up many different genes in a single biological calculation.  Also, if you aren't looking for a war weapon but rather a terror weapon, then you could target individual alleles known only from some small fraction of one single race, for example using miRNA.  Wnt (talk) 21:10, 10 May 2011 (UTC)


 * (from the original asker) Just wondering, the outbreak of SARS among east asians in 2003... a fluke of geography, or a genetic vulnerability? Why did so few non-asians get infected? Are there any differences in respiratory function or immune system response that were involved? 124.179.224.106 (talk) 21:46, 10 May 2011 (UTC)


 * It mainly affected Asians because it mainly affected Asia and it's mostly Asians that live in Asia... there is nothing more to it than that. --Tango (talk) 22:19, 10 May 2011 (UTC)


 * Actually, I have no idea at all why SARS didn't infect the world. The old idea I remember reading - that it was a nasty combination of coronavirus and paramyxovirus that eventually went their separate ways, immunizing the general public while giving them nothing more than a common cold - doesn't seem to have any support in literature that I'm reading now.  Did it evolve to become less damaging?  No idea.  But... whatever the reason, if SARS had a taste for Chinese, it should have infected a billion people, not 8000. Wnt (talk) 22:28, 10 May 2011 (UTC)


 * It's possible that Asians were more susceptible, say every 8000 per billion, while a lower percentage of the rest of the world's population would contract it, if occidentally exposed. StuRat (talk) 22:36, 10 May 2011 (UTC)


 * "Occidentally" - Badum, tish! {The poster formerly known as 87.81.230.195} 90.197.66.11 (talk) 07:27, 11 May 2011 (UTC)


 * On the topic of "races" and genetics, as others have noted, it's impossible to do so with any certainty, as the biological and social categories overlap a lot. However, it's not impossible to probabilistically look at a given human genome and say, "this person has genes that likely indicate their genetic origins from this part of the world." If you had a nanovirus or something that could process DNA in this way, you could make a disease that, say, had an 80% chance of infecting people whose genetic origins are in Southern Africa, and a 20% chance of infecting people whose backgrounds were predominantly European, or something along those lines. There would be a lot of overlap between your groups and it would be probabilistic in all cases. It would be a pretty stupid weapon to develop, given the amount of overlap between populations. If you wanted to exterminate large groups of people based on where they look like they are from, history provides many more effective and less R&D intensive "solutions" than this sort of thing. However I wouldn't put it beyond terrorist groups in the far future (though how far, I don't know — synthetic biology scares the bejeebus out of me for that reason), who wouldn't mind collateral damage. --Mr.98 (talk) 23:38, 10 May 2011 (UTC)


 * A major drawback of such genetically targeted bioweapons is the significant possibility that, once released, they could mutate and gain the ability to attack other "racial groups", including that of the user. {The poster formerly known as 87.81.230.195} 90.197.66.11 (talk) 07:35, 11 May 2011 (UTC)


 * Wasn't slavery in the United States before the civil war a very effective weapon that killed only one race? &#x2013; b_jonas 09:00, 11 May 2011 (UTC)


 * No, slaves were quite valuable and not killed off as a general rule. Plus, some of the pre-Civil War slaves were Native American rather then African.  Googlemeister (talk) 20:12, 11 May 2011 (UTC)


 * I don't think that mutation would be that big of a concern. First, any such weapon can be designed so that its damaging effects do not contribute to its reproduction, or even hinder reproduction to some extent - in other words, so that over time it will tend to mutate to become relatively harmless.  And more practically ... any situation in which one ethnic group starts finding it thinkable to use bioweapons on another is a situation where the other might be thinking about doing the same thing, meaning that they'd have worse than mutants to worry about.  Also, note that "mutual assured destruction" does not apply, because the weapon might be only incapacitating or annoying rather than absolutely lethal. Wnt (talk) 12:05, 11 May 2011 (UTC)


 * MAD may not apply, but deterrence still can. MAD is just an extreme form of deterrence. Fear of reprisals can apply even without MAD situations. --Mr.98 (talk) 14:21, 11 May 2011 (UTC)


 * MAA then, ("Mutually Assured Annoyance"). :-) StuRat (talk) 22:27, 14 May 2011 (UTC)

bending of space and time using lasers
can space and time of unit area be twisted using high energy lasers? if so why cant it be done in a tornado because space and time are being bent in a particular area that is inside the tornado? if so what would be the relativistic effects that would come into play in side the tornado? does the time dilation mass variation length contraction occurs ? —Preceding unsigned comment added by 175.110.91.49 (talk) 21:16, 10 May 2011 (UTC)
 * I have a feeling that I'm either A) being trolled, or B) in the presence of a Sci-Fi Channel movie writer. - Running On Brains (talk) 21:26, 10 May 2011 (UTC)
 * Oh no! An internet-user has maliciously enticed us to comment about subjects we are interested in!  No, there's no meaningful way to "bend space or time" using a laser.  You can read about the theory of energy density of electromagnetic waves; and you might be able to lure some of the more theoretical ref-deskers into a discussion of general relativity as it pertains to very high energy-density; but at least from a practical point of view, we have no laser technology today that could generate relativistic quantities of electromagnetic energy.  Even from a theoretical point of view, while high energy densities can have relativistic effects, I would not describe such effects as "twisting space and time."  Nimur (talk) 22:07, 10 May 2011 (UTC)
 * Why can't what be done in a tornado? There is a very big difference between space being twisted and air moving in a spiral pattern through space. There is nothing relativistic about a tornado. --Tango (talk) 22:21, 10 May 2011 (UTC)

Every photon in a laser beam does indeed bend space and time, by a very very very tiny amount. Blame Einstein. Hcobb (talk) 22:35, 10 May 2011 (UTC)

The most powerful continuous laser listed in the laser article is a 100kW laser claimed to be in development by Northrop Grumman. Even a 300 km (one light-millisecond) -long stretch of the beam produced by such a laser would only contain 100J of energy, which is equivalent via E=mc2 to a mass of only about a picogram. Sure, you can bend spacetime with that stretch of laser beam, but you can bend spacetime much more by using a single human cell, which has a mass of about a nanogram (see Orders of magnitude (mass)). Red Act (talk) 01:31, 11 May 2011 (UTC)


 * I've seen a video presented by Dr Karl Kruszelnicki showing an experiment he and some friends did where they worked on the reasoning that since gravity can cause light to curve, could curved light beams affect gravity? The quick answer is "No". Confusing Manifestation (Say hi!) 03:52, 11 May 2011 (UTC)
 * Well, no, not measurably. But it does an extremely tiny bit in theory.  Red Act (talk) 04:30, 11 May 2011 (UTC)

Now here is a more useful question: Given that a photon of light curves space around it and travels at the speed of light then it must leave behind a "shockwave" cone of a gravity wave at a 45 degree angle. So where does the energy required to make that gravity wave come from? Hcobb (talk) 05:15, 11 May 2011 (UTC)
 * The gravitational shock wave solution does not carry away energy from the photon. Some other issues are discussed here. Count Iblis (talk) 15:12, 11 May 2011 (UTC)