Wikipedia:Reference desk/Archives/Science/2011 December 24

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December 24

what travel is?

Base on our current technology, what is more likely to happen first.. Travelling thru time or travelling thru other galaxy in short period of time, (like going for a vacation in other galaxy). MahAdik _usap 01:15, 24 December 2011 (UTC)

That's easy. Under our current technology, traveling to another star (never mind galaxy) and living to tell about it, is impossible. Travelling through time is not only possible, but we're doing it right now. :) ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:17, 24 December 2011 (UTC)

(edit conflict) We already travel through time, but it is a one-way trip. Interstellar travel is a future possibility, though if we were to do it in a short amount of time that would, of itself, be its own form of time travel. An interesting treatment of the matter, if you are interested, is the song "'39" from the band Queen. It was written by the guitarist Brian May, who is also a trained astrophysicist and has a good grasp on the time-related issues of interstellar travel. --Jayron32 01:21, 24 December 2011 (UTC)

From what I read it's possible for subatomic particles at present to travel back in time. But no further than the start of the machine. I guess traveling through loopholes in space is more likely. Electron9 (talk) 06:20, 24 December 2011 (UTC)

I don't believe that is exactly correct. My understanding is that mathematical physics does not disallow negative time (backwards time travel), for example Closed timelike curves are hypothetically possible. Also, it is possible, in my understanding, to work the mathematics so that a particle described as having some "negative" properties to be mathematically equivalent to moving backwards in time. That doesn't mean that the particles actually travel backwards in time, just that the mathematics doesn't disallow it. The Chronology protection conjecture also has some interesting things to say on the matter. --Jayron32 06:31, 24 December 2011 (UTC)

Another area would be to be able to probe the past to see what really happened etc. Ie move information, not people. Electron9 (talk) 09:13, 24 December 2011 (UTC)

Moving information backwards in time (or, rather, arbitrarily moving information at a past point in time forward in time, to the present) is as prohibited by current science as moving people is. I wouldn't wait up for it. Also, it seems like kind of a bad idea. --Mr.98 (talk) 14:00, 24 December 2011 (UTC)

Probing the past wouldn't involve sending information backwards in time, it's about getting information from the past. We do that whenever we look at things - we see them as they were when the light left them. If you can set up or find a suitable mirror, you can see whatever you like at any point in the past (as long as it is long enough ago for the light to have reached you in a straight line). --Tango (talk) 14:26, 24 December 2011 (UTC)

You could hypothetically set up a mirror today which would reflect information about today into the future, so that future people can investigate what happened today (whether this is technologically possible is neither here nor there. It is merely not disallowed by the physics). What you cannot do is outrace the light from the past and install a mirror to catch that light and reflect it to today. That train has already left the station, as it were. --Jayron32 15:31, 24 December 2011 (UTC)

The theory would be to either somehow reconstruct or retrieve photons from the past. So maybe you could actually watch famous events or find out details otherwise impossible to find out. The other approch is to exploit some quantum or subatomic particle interaction such that past events can be sufficiently reconstructed.Electron9 (talk) 17:24, 24 December 2011 (UTC)

That's where finding the mirror comes in - a black hole in just the right position could cause the light to do half an orbit around it and come back the way it came. It's unlikely that you could find one just where you wanted it, but it's physically possible. --Tango (talk) 20:04, 24 December 2011 (UTC)

The universe is huge so the probability isn't that low. But finding such gravity object, and most of all being able to get any useful signal-to-noise light might be harder .. ;) Electron9 (talk) 22:26, 25 December 2011 (UTC)

Assuming the OP means travelling in time at an arbitrary and possibly negative rate, going to another galaxy is "more" likely, with "more" in scare quotes because both are completely impossible with any technology we have now or will have in the foreseeable future. The difference is that travelling to another galaxy in a (subjectively) short time is at least theoretically possible due to time dilation, whereas our current understanding of the universe essentially prohibits backwards time travel entirely. Forward time travel at a rate noticeably greater than one second per second doesn't require any technology that is very far beyond what we have now, and is even a prerequisite to getting anywhere out of the solar system in a reasonable subjective time-frame. Of course, going for a vacation in another galaxy sort-of-implies returning and expecting to see Earth more or less as you left it, which requires backwards time travel anyway. We do have some ideas on how backwards time travel could be possible, but they tend to involve negative mass (and lots of it, too), which probably doesn't exist in any usable form. The Casimir effect might work (see the section "Wormholes" in that article), but even then, the effect is so incredibly tiny compared to the vast negative energies required for wormholes or Alcubierre drives capable of transporting a human (plus life support systems, baggage, etcetera) that I'd say hyperrelativistic spacecraft are still more feasible. --Link ^(t•c•m) 10:24, 24 December 2011 (UTC)

Travelling backwards in time and travelling faster than the speed of light (which I expect are the two things you are really asking about) are essentially the same thing, according to general relativity (just from a different point of view). If we can find a way to do one, it will probably allow us to do the other as well (not definitely, because if we do find a way to do one of them, it could be because general relativity is wrong so they aren't necessarily equivalent after all), so I would say they are equally likely (which is to say, both extremely unlikely). --Tango (talk) 14:22, 24 December 2011 (UTC)

The theory regarding speed of light seems to been broken by neutrinos this year. Other discoveries may show up. Is negative mass different from anti-matter? Electron9 (talk) 17:24, 24 December 2011 (UTC)

Chances are there is something else going on with those neutrinos rather than them actually violating a fundamental principle of special relativity. Anti-matter has positive mass, but opposite electric charge. Matter with negative mass is often called exotic matter and there is no evidence that it exists. --Tango (talk) 20:00, 24 December 2011 (UTC)

They're the same thing. If you can move faster than light, you can go one way, change your point of reference, go the other way, and end up where you started before you left. If you can go back in time, you can go to another galaxy the slow way, then go back in time to "when" you left (scare quotes due to the relativity of simultaneity). Admittedly, that second one isn't very useful if you don't have cryonics or some other way to make taking a trip like that not seem to take forever. I suppose you could take the trip really, really fast, so time dilation makes it seem like it doesn't take very long. — DanielLC 07:50, 25 December 2011 (UTC)

Differnce

Whats the diff betweemn virginal hypertrophy and macromastia. And where can i get pics?--213.98.69.99 (talk) 14:20, 24 December 2011 (UTC)

Have you read Hypertrophy of breast? If not, start by reading that and then come back if you have any further questions. --Tango (talk) 14:23, 24 December 2011 (UTC)

Whats Zena Fulsom suffering from?--213.98.69.99 (talk) 00:00, 27 December 2011 (UTC)

The article was deleted several times; one deleted version stated she was a fictional porn actress. ~AH1 ^(discuss!) 03:02, 27 December 2011 (UTC)

Is it true that electricity was originally used almost exclusively for just lighting?

Topic says it all. ScienceApe (talk) 14:47, 24 December 2011 (UTC)

I don't know about that. Electricity was vital to the Electrical telegraph, and that was in widespread use several decades before Edison's light bulb was. --Jayron32 15:26, 24 December 2011 (UTC)

Domestically, it may be true, though. I think when houses were first being connected up to electricity supplies, it was primarily for lighting. Edison played a key role in setting up the first mains electricity supply, so I wouldn't be surprised if it went along with his light bulb. The relevant article seems to be History_of_electrical_engineering#19th_century_developments, but it's a little light on details (no pun intended). --Tango (talk) 15:38, 24 December 2011 (UTC)

Ah, I can do better than that. Electricity_distribution#History says: "Low DC voltages were used (on the order of 100 volts) since that was a practical voltage for incandescent lamps, which were the primary electrical load." It doesn't say it was exclusively used for lighting, but it was primarily used for lighting (in the domestic setting - obviously there were telegraphs and other specialist uses as Jayron mentions). --Tango (talk) 15:44, 24 December 2011 (UTC)

Electric lighting was the killer app for electricity in the early days of domestic use. Edison gets a lot of credit for inventing the light bulb (which is only partially true), but he ought to get the most credit for creating the first electricity infrastructure. --Mr.98 (talk) 01:15, 25 December 2011 (UTC)

The first public electric utility was in New York (Edison's), the first use of electricity being for light (residential and commercial) and power (commercial enterprises using electric motors). Used to walk past the building all the time when I worked in downtown NYC. PЄTЄRS J V ►TALK 03:18, 25 December 2011 (UTC)

Another late-19th century invention was the Tesla coil, which led to further developments such as wireless communication and the spark-gap transmitter. ~AH1 ^(discuss!) 03:01, 27 December 2011 (UTC)

evolution

if any one gives me a Wikipedia article on this, it's enough. I saw a youtube video in which the uploader claims that there is no known mechanism under which genes "add", and goes on to compare the number of genes in humans and bacteria.Now even if he/she is right, it doesn't disprove evolution, just because of something we don't know YET, but... is it true?--Irrational number (talk) 20:30, 24 December 2011 (UTC)

How about gene duplication? --69.113.197.155 (talk) 20:36, 24 December 2011 (UTC)

is it the only one?--Irrational number (talk) 20:52, 24 December 2011 (UTC)

Genome#Genome_evolution is a good starting point, also be sure to check out horizontal gene transfer. --69.113.197.155 (talk) 22:34, 24 December 2011 (UTC)

Also check out polyploidy. It's not that common in animals, but 30-80% of plants are polyploid. --99.237.252.228 (talk) 00:43, 27 December 2011 (UTC)