Wikipedia:Reference desk/Archives/Science/2008 October 31

= October 31 =

Why is space so big?
I mean, isnt the distance just....overwhelming? You cant wrap your mind around it! Just think about how big a light year is. The distance that light travels in a freakin' year, that's what! That's 11,600,000 miles in just one minute! ....Wow Wow Wow...When we say that something is millions of light years away, I just...can't comprehend it.--Sunburned Baby (talk) 02:56, 31 October 2008 (UTC)


 * Space is so big because its been around for a long time. If we consider that the availible evidence tells us that the universe is expanding, and since we know about how fast it IS expanding and about how long it has been expanding, we get an estimate for how big the whole thing is.  And the answer is REALLY FREAKING HUGE.  No shit.  I used to teach an Earth Science class, and for the astronomy unit, I would take the kids out to the football field to map out the solar system.  If you put the sun at one goal (endzone or soccer goal, its about the same size) and put pluto/neptune at the other goal/endzone, then on that scale the sun is the size of a Quarter coin, and the earth is about the size of a speck of sand.  And that's ONLY our solar system, which if scaled to such a size so that the galaxy could fit on a football field, the entire solar system would be a speck of sand.  And if we put our galaxy on a football field scaled to teh size of our local group of galaxies, it would be a speck of sand, and so on and so on.  Feeling insiginficant yet?  --Jayron32. talk . contribs  03:14, 31 October 2008 (UTC)


 * Another issue is safety. From the Anthropic principle we know that we have not been wiped out by a gamma ray burst or stray star or black hole, so they have to be far away from us. Graeme Bartlett (talk) 03:17, 31 October 2008 (UTC)


 * I never know whether saying "the volume of the observable universe is around 3×1080 cubic meters" makes the size seem more or less comprehendable. At least I can actually consider how immense that is, rather than saying "larger than I can imagine", but then I have troubles imagining 1080. DMacks (talk) 04:11, 31 October 2008 (UTC)

Often when one gets a question like this it makes sense to invoke the anthropic principle and assert that if it weren't just so then life as we know it wouldn't be here to observe it. However I'm not sure if that is the case here. What if instead of being 3 m/s, the speed of light were only 3 m/s ? The visible universe would be 1/10000 the diameter it is now, but would it really matter? We'd expect our new universe to have room for ~1 galaxy, but who needs the other galaxies anyway? Satellite communication might suck, and microchips wouldn't be as speedy, but does life as we know it really require such a large c?

As far as I can tell, the answer would appear to be no. Are there any really fundemental downsides to envisioning a universe with a much slower speed of light (and hence a universe that grows much more slowly)? Dragons flight (talk) 04:28, 31 October 2008 (UTC)
 * The point is that the processes that created our galaxy require a universe with more than just our galaxy. Our galaxy exists only because the processes that create galaxies require a universe which is pretty much exactly the size it is now, with a fundamental speed of light equal to exactly what it does in our universe.  If the laws were not so, the conditions would not exist to create the Universe as it is, with us studying it.  Its not just about whether or not we could survive in a 1-galaxy universe with a slower speed of light; we could, its that such a universe could not have come into being in such a manner as to create the necessary conditions for life to exist.  The Anthropic Principle is a bit of a tautology, but a useful one.  --Jayron32. talk . contribs  04:45, 31 October 2008 (UTC)


 * That's merely an assertion, not an explanation. What about the big bang and structure formation requires lots of space?  Galaxies nucleate from primordial density fluctuations that would presumably still exist.  The necessary mass only comes from a sphere ~10 times wider than the ultimate disk of the galaxy itself.  I don't see any reason all that other distant mass is actually necessary to forming a galaxy.  As best I can tell, the dynamics of galaxy formation don't require the universe to be huge.  Dragons flight (talk) 05:06, 31 October 2008 (UTC)


 * Having a small speed of light would also affect speed of gravity, and a galaxy may not form as big as we know it. Then you may find a lack of heavy elements needed to make planets and humans. We also need plenty of space to make a cold background in the sky, so that solar energy can drive life on earth. Graeme Bartlett (talk) 05:36, 31 October 2008 (UTC)


 * Look man, space is big. Really big. You just won't believe how vastly hugely mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space. Listen: When confronted by the sheer enormity of space, better minds than the ones responsible for this reference desk have faltered. Some invite you to consider for a moment a peanut in Reading and a small walnut in Johannesburg, and other dizzying concepts. The simple truth is that interstellar distances will not fit into the human imagination. :) --Shaggorama (talk) 05:51, 31 October 2008 (UTC)


 * I can easily envision space being much much much bigger say a googleplex times as wide or maybe another power or two than that. Why is it so small relative to us? Perhaps it just couldn't be any smaller. Dmcq (talk) 09:06, 31 October 2008 (UTC)
 * You mean googolplex right? ;) —Cyclonenim (talk · contribs · email) 10:34, 31 October 2008 (UTC)
 * Big can be looked at in other ways too: which is more, stars in the Milky Way or cells in a single human brain? stars in the Universe or bacteria in the oceans? Franamax (talk) 09:33, 31 October 2008 (UTC)
 * My very quick research shows there are about 2-4 times as many stars in our galaxy as there are neurons in the human brain (I don't know about other cells). I have no idea how many bacteria there are in the oceans, though... --Tango (talk) 17:22, 31 October 2008 (UTC)
 * You need to be careful when considering what would happen if a physical constant were different. All the constants are interrelated, so if you're changing the speed of light you're going to have to change some others as well. What would happen will depend on which ones you change and in what way. There is a way of doing it (I don't remember the details) that results in pretty much no observable change at all because it results in atoms being 10,000 times smaller, and therefore everything else is 10,000 times smaller (that doesn't follow exactly, but I think the conclusion is still correct) so the time it takes for light to get from A to B is unchanged since A and B are just closer together. --Tango (talk) 10:43, 31 October 2008 (UTC)


 * "Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space." - Douglas Adams 88.211.96.3 (talk) 11:25, 31 October 2008 (UTC)
 * Space is so big I totally didn't notice someone had a more complete version of this quote above me! 88.211.96.3 (talk) 11:46, 31 October 2008 (UTC)


 * Space is big to protect the rest of the universe from us Adambrowne666 (talk) 11:33, 31 October 2008 (UTC)


 * Which seems fairly complete. In the absence of faster-than-light technology, which seems unlikely to say the least, humans are just not really going to get very far as a species in space. Look upon "we'll colonize space!" proposals with a gimlet eye unless someone suggests a really plausible explanation of how we'd get significant numbers of people (e.g. significant breeding populations) anywhere useful within the lifetimes of those traveling. --98.217.8.46 (talk) 13:26, 31 October 2008 (UTC)


 * I believe the trick is NOT to try to do it in the lifetimes of the people inside. We need huge, landscaped, spinning (for artificial gravity) mini-worlds made from hollowed out objects from the 'belt - each with LARGE populations (thousands of people at a minimum).  Power will have to be from fusion sources to keep the fuel supply compact enough - and the progress from one star to the next has to be expected to take thousands of years.  It seems inevitable that such habitats will be needed in the future - and once there are enough of them in solar-orbit - it's only a matter of time until one of them takes on the trip.   If you are living your life in such a place anyway - it may not make much difference to you whether you are orbiting the sun - or heading off to Alpha Centauri with no hope of arriving during your lifetime.


 * An alternative (which is perhaps more likely to be of interest and I'm fairly sure will happen in the next 100 years) is the "scan your brain - produce an exact software simulation of it - then die". "You" will continue to exist with all of your thoughts and memories intact inside a computer somewhere - presumably with some kind of robotic body with robotic senses.  You feel like you are still "you" and your family and friends can easily tell it's still you - and you behave pretty much like any other human - albeit in that robotic body.  Now we can do a couple of interesting things:


 * Shoot a small, unmanned probe to the next star. It's small - it gets there in 100 years and proceeds to drop off some handy robots.  When it arrives, we transmit a colony of humans by radio or laser communications to the probe and thence to the robots.  Elapsed journey time is at the speed of light - but to the traveller it would seem instantaneous.  When you arrive, you live out your life in a robotic body - and if you want to return - you simply transmit yourself back again as another radio signal and you're home again in the blink of an eye.  The travel time is still at the speed of light - so it's gonna take 4 years to go and 4 years to come back from Alpha Centauri - but 8 or 9 years away is not so terrible if you don't have to endure the journey.
 * Using a very small probe - shoot a computer and a robot body to the nearest star. But have the computer's clock rate be adjustable.  When there is nothing much happening, it executes one instruction every second - when there is an emergency - or at the start and end of the journey - it runs at a few teraflops.  Your brain can 'fast-forwards' through the boring parts and consume almost no energy - and zero other resources.   When you arrive, you ramp the clock up to full speed and download yourself into the robotic body to do whatever exploration you fancy.   Sure - it takes hundreds of years to get there and to get back again - but you won't die of old age and you won't get bored.


 * Once you can 'fast forward' your life through the boring bits and have your thoughts and memories transmitted and reconstructed at the speed of light - you can live as long as you want to - and there are a LOT of interesting possibilities.


 * SteveBaker (talk) 19:12, 31 October 2008 (UTC)


 * A wonderful Star Trek-like solution, but the humans you imagine have little to do with any humans I have ever seen. Make a big dome, put a few thousand humans inside it, wait a few weeks and they'll be in a state of civil war, disrepair, disaster. I don't see us getting off this planet in any major way. The human race will, at some point, go extinct—of that there cannot be any question. Once you accept that it just becomes a question of when and where. --98.217.8.46 (talk) 21:12, 31 October 2008 (UTC)
 * There are plenty of remote groups of humans with populations under 1000 who manage just fine. The Pitcairn Islands had a rough start - but they survived and thrive today with almost no contact with the outside world and only just barely enough genetic diversity to keep going. I don't see the need for passimism in that regard.  As for the "humanity" of the humans I imagine - well, I think what matters is our intellects - and what I suggest would preserve that in the purest way possible.  You might think we couldn't survive that - yet wikipedians talk via the clunkiest links - form friendships - and seem in every way "human" - even though we rarely meet face to face.  If my brain was merely simulated on a big computer - I don't see how you could possibly tell. SteveBaker (talk) 01:48, 1 November 2008 (UTC)
 * The pitcairns are a rubbish example - Pitcairn sexual assault trial of 2004 86.150.196.186 (talk) 15:40, 1 November 2008 (UTC)
 * Sure, they have their problems - it's inevitable. But recall that I was responding to: "wait a few weeks and they'll be in a state of civil war, disrepair, disaster"...and after 200 years, the Pitcairns are not only NOT in a state of civil war, disrepair OR disaster - but they actually have a legal system, a school and so forth.  I don't pretend that a community of a thousand humans heading off for a thousand years in the direction of Alpha Centauri wouldn't have problems - sure, there will be criminals, there will be horrible divisions about matters of policy - but they can deal with that if they have no alternative - and the Pitcairn Islanders are about as close to that situation as I can easily find information about.  But small tribes out in the Amazon have also been found who have been more-or-less cut off from other humans for centuries and are doing OK. SteveBaker (talk) 17:41, 1 November 2008 (UTC)


 * This can't be allowed to pass unnoticed : "If [SteveBaker's] brain was merely simulated on a big computer - I don't see how you could possibly tell."APL (talk) 16:58, 1 November 2008 (UTC)

Photons and Phonons
In special relativity, light are waves, and the inertia of objects increase as the velocity of objects increase toward the speed of light. sound are also waves, so do the inertia of objects increase as their velocity increases towards the speed of sound? —Preceding unsigned comment added by Superwj5 (talk • contribs) 12:14, 31 October 2008 (UTC)


 * Short answer, no. You get interesting aerodynamic effects as you approach and pass the speed of sound (sonic booms, etc), but nothing relativistic. While light and sound are both waves, they are very different things - sound is compression waves in a medium (air, usually), light doesn't have a medium, it's just self-propagating electric and magnetic fields. Light is a fundamental feature of the universe, sound is just a consequence of vibrations in matter. --Tango (talk) 13:19, 31 October 2008 (UTC)

Bosenova
Does anybody even have any evidence what Bosenovae really are? Or at least some possibilities and guesses? I think they might have entered an unknown interaction and changed into sparticles, bosinos or dark matter or perhaps the magnetic field stuck some of the atoms into their Schwarchild radius in quantum gravity and Hawking radiated into other stuff? Do you have any idea what it is? —Preceding unsigned comment added by Superwj5 (talk • contribs) 12:22, 31 October 2008 (UTC)


 * Apart from what the Bosenova article says, no people don't know exactly. But you'll find proposed theories on it if you search arxiv.org and scholar.google.com. For instance, Phys. Rev. Lett. 89, 180403 (2002) Mean-Field Theory of Feshbach-Resonant Interactions in 85Rb Condensates implies 'rogue dissociation. For a definition, see arXiv:physics/0607075v1 but simply put the atoms in the bose einstein condensate spontaneously turns into molecules, which are then repelled. This process is more likely at certain densities than others. EverGreg (talk) 14:34, 31 October 2008 (UTC)


 * Are you Blaming it on the Bosenova? What did Eydie Gormé ever do to you?!? --Jayron32. talk . contribs  18:00, 31 October 2008 (UTC)

Rockets underwater
Why don't rockets work underwater? 98.221.85.188 (talk) 16:06, 31 October 2008 (UTC)


 * The basic principle will work - you throw something out the back you'll get an equal and opposite reaction pushing the rocket forwards. However, resistance from the water would make an underwater rocket extremely inefficient, probably to the point of being useless. The same is true of air, to a lesser extent, rockets are significantly more efficient in a vacuum than in the atmosphere. That's one of the reasons for taking off vertically and then going sideways to enter orbit, rather than taking off diagonally to start with - you spend less time in the atmosphere. Propulsion underwater usually involves taking in water from the front and expelling it out the back (eg. using a propeller), that turns out to be far more efficient that expelling rocket exhaust out the back. --Tango (talk) 16:37, 31 October 2008 (UTC)


 * They do! See VA-111 Shkval.  --Sean 17:00, 31 October 2008 (UTC)


 * Yeah, what are you guys talking about? Rockets work just fine under water. They just don't move as fast. Missiles are routinely launched from submarines underwater, and you can fire a fireworks rocket or Estes model rocket into a swimming pool and observe that it still works. ~Amatulić (talk) 21:01, 31 October 2008 (UTC)


 * Sure - the distinguishing difference between a rocket and a jet is that a rocket contains it's own oxidizer. Hence it likely burns just fine underwater.  Gasses still shoot out of the back pretty quickly - and Newton's laws guarantee that if something shoots out of the back - it WILL go forwards.   The only question is thrust-versus-drag ratios that will affect your accelleration and top speed underwater.  SteveBaker (talk) 01:37, 1 November 2008 (UTC)

How to select motor rating for pure electric vehicle
(moved from Village pump). If i want to replace a 150cc IC engine base two wheeler with an electric vehicle run by a direct drive motor what rating of motor will i have to use??? Is there a direct relation between cc and kW of the machine??? Any help please??? —Preceding unsigned comment added by LifestyleBangalore (talk • contribs) 16:38, 31 October 2008 (UTC)


 * Try to find an equivalent horsepower or kW rating. The cc number for an engine tells you very little about the power it can produce these days.  It's a bit more complex than that though - electric motors have spectacular low-end torque - so you can get really great 0-60 times with a fairly wimpy little motor - but then find that your top speed sucks.  That may not matter if you do lots of in-town driving and very little freeway - but it's easy to be fooled by those kinds of numbers.  Also, without a gearbox, you need a very flat torque curve across the entire RPM range - electric motors are pretty good at that - but some are much better than others. SteveBaker (talk) 18:03, 31 October 2008 (UTC)

Customizable open office walls
What kind of walls can be used to divide an open office?--Mr.K. (talk) 18:20, 31 October 2008 (UTC)
 * They're usually referred to as "Office Partitions". A google search will get you loads of suppliers sites, and an image search lets you see the variety on offer. Fribbler (talk) 18:26, 31 October 2008 (UTC)
 * Cubicle and (sadly) Cube farm. SteveBaker (talk) 18:49, 31 October 2008 (UTC)


 * Not all open office dividers are "cubicles". My office is a donut design.  The elevators, plumbing, and main cabling are in the middle.  Offices are around the outside windows.  They are divided using full-height walls and doors that appear to be real fixed walls.  The advantage is that the maintenance people can move walls around to enlarge or divide offices as needed. --  k a i n a w &trade; 21:11, 31 October 2008 (UTC)


 * "Oh look, see, its not a square office, so your not a mindless paper-pushing drone like those people who have to work in cubicles. See, you mean something as an individual cuz you work in a round building!".  Industrial psychology writ large... --Jayron32. talk . contribs  02:35, 1 November 2008 (UTC)


 * Is that worse than: We took out all the cubicle walls so you can see your coworkers all the time and have no privacy at all because who needs privacy when we're all one big happy family. -- k a i n a w &trade; 16:58, 1 November 2008 (UTC)


 * My perception of quality-of-life at the workplace has been largely independent of the various office layouts I have experienced. With large offices containing dozens or hundreds of employees with individual preferences, it will be hard to maximize the layout-to-happiness quotient (first you have to find some way to measure that).  I tend to think that a lot of employees complain about all office layouts, and have no real motive other than whining.  Nimur (talk) 18:30, 3 November 2008 (UTC)

Electromagnetic pulse
In sci-fi, whenever there is an EMP everyone runs around frantically turning everything off. Does that actually help? If so, how? My understanding of the relevant physics suggests it wouldn't (and the unreliable sources I've found via google tend to agree), does anyone know for sure? --Tango (talk) 22:15, 31 October 2008 (UTC)


 * That makes as much sense as space ships executing banked turns in weightless vacuum, or having high-current power lines running behind display panels so they emit showers of sparks when something bad happens.


 * No, turning things off after an EMP event accomplishes nothing. It may help to power-off stuff before the pulse. In my industry, we can incorporate nuclear event detectors that cause critical equipment to switch off automatically, to protect them from EMP, and the equipment itself is designed to be "hardened" against such events in the first place. ~Amatulić (talk)
 * Sorry, I should have said "whenever there is *going to be* an EMP", obviously turning things off after they've been fried isn't going to help. --Tango (talk) 22:48, 31 October 2008 (UTC)


 * I think the OP is asking, "does EMP only affect things that are turned on in the first place". I mean, does turning things off change anything if they are not hardened to EMP in the first place? --98.217.8.46 (talk) 22:51, 31 October 2008 (UTC)

There is absolutely no doubt that EMP is "real". In the early 1960s, computers used clunky 'Ferrite core memory' technology. You could literally see the individual bits as little grey donuts threaded on wires. One interesting thing about core memory is that it's magnetic - and if you turn your computer off and back on again, it doesn't wipe the memory as happens with "DRAM" technology. As core memory became obsolete, the very last application of it was in military aircraft that were designed to deploy nuclear payloads. After they dropped "the bomb" - and turned around to get the heck out of there - the aircraft stood a chance of catching the EMP from it's own weapon. Hence they used core storage in their flight computers - so that the computer could be turned off and rebooted without losing a beat.

What an EMP does is to induce voltages in metal objects in its path. If you are close enough - and the geometry of the metal is just right - that voltage may be large enough to disrupt or destroy the circuit. Whether turning it off helps has to depend on an awful lot of things. Let's imagine some delicate piece of electronics with two LONG wires going off to a switch and a battery. If the wires lie in one pattern then the voltage will be induced between the battery/switch and the electronics - and both ends of the wire that contact the electronics could be at the same voltage - the electronics themselves might be small enough to to pick up any significant voltage at all. In that case, the electronics are probably undamaged. If we imagine another situation where two wires lead out of the electronics in opposite directions then the induced voltage could be large and fry the electronics instantly. If the switch happens to be up close to the electronics - and breaks the physical connection between the long wires and the electronics - then sure - turning it off beforehand ought to reduce the risk...but it's certainly not going to ensure it'll be undamaged. Turning the switch off AFTER the pulse has passed is obviously pointless though.

So - if you know an EMP is coming - I guess you should turn off anything you can get to in time - there is no guarantee it'll help - but then there is no guarantee that an EMP will destroy everything electronic/electrical anyway.

SteveBaker (talk) 01:29, 1 November 2008 (UTC)


 * So the key thing is not so much to have things switched off as to have them unplugged (or otherwise isolated from the long wires), so if you have a laptop running off its battery, it's not going to matter whether it's on or off? --Tango (talk) 01:54, 1 November 2008 (UTC)


 * Yes exactly. Most things plugged into the power grid will likely be fried - an EMP crossing those mile-long power lines (or even the shorter ones that go into your house) induces one heck of a voltage. The longer the conductor, the more voltage induced for a given EMP. I think the "magic number" is 30 in for nuke-level EMPs to damage sensitive electronics. Not sure what era's electronics that was for though. Arakunem Talk 14:47, 1 November 2008 (UTC)


 * In those sorts of stories no one ever runs around disconnecting antennas. Personally, I'd do that first. APL (talk) 16:47, 1 November 2008 (UTC)

Age of Aneurysms?
I'd like a little more information about aneurysms that I couldn't find in the article. First, what ages can get them? Can you even have them from birth? I know the article did mention men have a higher risk than young women, but would it still be reasonable for a teenage girl to have an aneurysm? Also, if they burst, does it always lead to death? Thanks for the help! 71.13.209.44 (talk) 22:40, 31 October 2008 (UTC)
 * Aneurysms can be present from any age, as far as I'm aware. I read a case study of a 1-month year old male who had one, so it is possible, but the risk increases significantly with age and aneurysms in paediatric patients are rare. If you're asking about teenage girls having aneurysms, and you are that teenage girl, I strongly suggest you seek the help of a doctor. It is possible for a teenage girl to have an aneurysm, but again, it'd be rare at such a young age. If an aneursym ruptures, a lot of factors can determine the outcome. Where was the aneurysm? Aneurysms in the brain feature high mortality rates, same with the aorta (this one in particular is incredibly high without prompt medical treatment). However, they do not always lead to death —Cyclonenim (talk · contribs · email) 23:15, 31 October 2008 (UTC)
 * No, I'm actually looking up some stuff for a friend's NaNoWriMo book! But thanks, that helped a lot! 71.13.209.44 (talk) 00:30, 1 November 2008 (UTC)


 * Wish your friend luck! I never won an edition of NanoWrimo, so if your friend does, they're already a step ahead of me. - Mgm|(talk) 22:31, 1 November 2008 (UTC)