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Travel at light speed? Almost certainly not, for anything with rest mass.
Travel faster than light speed? Seems to have some rather extreme practical barriers, but the theoretical status is somewhat up in the air.
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I think the term "Travel" doesn't really apply when talking about faster-than-light, as the term generally doesn't refer to actually accelerating in the traditional sense. Faster-than-light generally refers to going "Around" (Wormholes, quantum entanglement, etc) space-time and so, getting information to a point faster than Light would be able to by traditional means.
As far as ACCELERATING to the speed of light, it isn't possible according to Relativity as, the faster you go, the more energy it takes to accelerate. As you approach light speed, the amount of energy needed to go faster approaches infinity. Lets face it, there just isn't infinite energy out there to be had.
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So if you slow light down in say a gel or something, how does it get back to its normal speed if it's impossible to accelerate to the speed of light? Or is this because it doesn't have any mass?
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OK. But if i made a sspce shift, with a giant engine, that held a star.Then the star went supernova and i used that to propell me! I'm so going faster than the speed of light
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Yes i am, your pesstimistic comment has made me want to strive to succeed and whatnot. So, yes i am.
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The speed of light not in a vacuum is the speed of it to cross while in that substance . . . which means while doing things like being absorbed/retransmitted by particles. The speed while in the vacuum parts of the substance is still the same.
Bok: if I understand the (most basic) equations right, there's nothing preventing much faster than light travel for rather longer. As noted, the barrier is acceleration, not travel. If one could reach that speed without accelerating through the intermediary steps (ask me not how ), it could theoretically be continued.
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*shrug* Its rather simple. All you need to do it set 'c' to something manageable like 10km/hour. I recommend 'setenv'.
Posts: 7593 | Registered: Sep 2006
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We really should specify "speed of light in a vacuum". In 1999 the Danish physicist Lene Vestergaard Hau created a Bose-Einstein condensate in which the speed of light was 38 miles/hour. I have traveled faster than that on my bicycle (although not in a Bose-Einstein condensate).
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So I just looked into it and Lene Vestergaard Hau's team has recently managed to transform light into matter and back using a Bose-Einstein condensate. If that is possible, it should also be possible to transform matter into light and then back into matter which would effectively facilitate the tranport of matter at light speed.
I'm not an expert on the details of this but if you could transform matter into light using a Bose-Einstein condensate, then allow the light to travel through a vacuum to another Bose-Einstein condensate where the light was transformed back into matter, wouldn't that be very nearly equivalent to accelerating the matter to light speed?
And while I'm sure the Harvard teams experiments required a seriously large amount of energy -- it was certainly only a finite amount.
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quote:So I just looked into it and Lene Vestergaard Hau's team has recently managed to transform light into matter and back using a Bose-Einstein condensate. If that is possible, it should also be possible to transform matter into light and then back into matter which would effectively facilitate the tranport of matter at light speed.
This is not an accurate understanding. 'Transform into matter' just means 'convince some atoms to hold the photons for a long period of time'. The pulse of light is effectively 'stored', but more in the way energy is stored in a battery than in any transformative sense. In particular, while there is a natural equivalence between light and a particular arrangement of matter, there is not any such equivalence between matter we would be interested in transferring and light.
Not to mention that, if we wanted the matter to be 'identical' at the other end, we could only transmit through passages completely void of matter. Otherwise the light would be distorted. Heck, even if the passage is completely void, gravitational distortions would probably be too much over long distances.
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quote:Originally posted by The Rabbit: So I just looked into it and Lene Vestergaard Hau's team has recently managed to transform light into matter and back using a Bose-Einstein condensate. If that is possible, it should also be possible to transform matter into light and then back into matter which would effectively facilitate the tranport of matter at light speed.
So is this like a Star Trek transporter then?
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What people have said about the possibility of travelling faster than light, if only you could get there without accelerating through c, is perhaps a little optimistic. It tends to assume that the equations of special relativity hold for particles travelling faster than light - in particular, we look at 1 / (1 - v^2/c^2) and observe that this is only undefined if v = c. Well, yes, but that's mathematics. We have absolutely no idea what the physics will do at v > c, because we've never observed it. There is really no reason either theoretical or experimental to extend special relativity into that regime. If you like you can postulate an entire universe of faster-than-c particles, with equations governing their motion that make it impossible for them to decelerate below c. And, no doubt, people on faster-than-c intertubes speculating that "if only we could get there without decelerating, slower-than-c travel should be possible!" Then you can start saying "Hmm, we've got all this dark matter we need to explain..."
Or you could stick to the Invisible Pink Unicorn, which has some usefulness as a theological argument.
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(We actually have accelerated protons to within signifigant fractions of c (99+%). The protons gain mass as more energy is put into them instead of going faster.)
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If I remember correctly, the Bose-Einstein condensate was possible because the substance was cooled to within a few billionths of a degree of absolute zero. I suspect that a lot of really nifty stuff would be possible in absolute zero. After all, the point at which molecules stop moving seems pretty significant to me.
Posts: 636 | Registered: Apr 2002
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quote:Originally posted by The Rabbit: So I just looked into it and Lene Vestergaard Hau's team has recently managed to transform light into matter and back using a Bose-Einstein condensate. If that is possible, it should also be possible to transform matter into light and then back into matter which would effectively facilitate the tranport of matter at light speed.
So is this like a Star Trek transporter then?
I read the nature article and its pretty clear that the matter --> light --> matter transition couldn't work using the same technology that Vestergard Hau used. I still think that if the matter-->light transition is possible and the light-->matter transition is possible (which they demonstrably are from Vestergard Hau's work), thye matter-->light-->matter transition should be possible in theory. There is however an enormous gap between theoretically possible and technologically possible.
There is also the little glitch that the matter must be in a Bose Einstein condensate (i.e. be essentially at absolute zero) which is bit colder than most people find comfortable.
[ May 21, 2008, 09:47 PM: Message edited by: The Rabbit ]
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There's the formula for traveling at the square of the speed of light. Should get you almost anywhere in the galaxy relatively instantly. So you go ahead and dived your energy by your mass, and off you go.
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Nothing in Hau's experiment suggests arbitrary matter can be turned into light (much less back into matter) at all. All they did is store photons in the energy of atoms. That happens all the time, just for shorter periods of time. It is why light takes longer to travel through matter. As matter is not made of photons, the technique is absolutely unrelated to turning arbitrary matter into light.
Feel free to believe it is possible, but the Hau experiment is not experimental support in the slightest. Nothing in the transition you suggest is demonstrably possible from Hau's work at all.
edit: to hopefully be clearer, at no point in Hau's experiment did the number or configuration of atoms change (while the Bose-Einstein condensate was present). Some of the atoms had electrons with increased energy for a prolonged period of time, due to absorbing photons. After that time, they emitted the photons in much the same way as the photons originally entered the condensate. This happens all the time, such as when we shine light through glass, except that is for a much shorter period of time. Since apples' existences are not manifestations of increased electron energy, this experiment does nothing to show that they can be translated to light (at least, no more than shining a flashlight through glass does).
Posts: 15770 | Registered: Dec 2001
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I suspect that if there ever is something that allows us to travel at apparent faster-than-light speed, it will have to be something like the concept of 'Outside' found in the continuation of the Ender series.
In a sense, if I interpret correctly, that is what they theorize wormholes do. You are at one location in the universe, you enter the wormhole and exit in a new location in another part of the universe. The linear real distance between those points being completely disproportionate to the apparent time and distance through the wormhole.
With the advancement of String Theory, and I confess my knowledge is very limited, it seems that 'strings' exist in 11 dimensions. Those dimensions while not part of our physical reality, are attached to what we perceive to be physical reality. If we could step into one of those other attached dimensions, much like Ender and the gang stepping Outside, we could re-enter our reality in a new place. Again, the linear distance being completely disproportionate to the perceived time and distance.
This may seem like total science fiction, but remember that today we are surrounded by impossibly magical things; things that are beyond the comprehension and even imagination of people who were born early in the 20th century.
Look at the change in technology from 1900 to 2000. What a stunning era to live in. Now imagine similar changes occurring between 2000 and 2100. What an amazing world that is going to be, sadly I will certainly not live long enough to see it.
I think the first thing on our road to that techo-evolutionary surge is for the age of petroleum to come to an end. It must go the way of the horse, buggy, and steam train.
I see hints of astronomically efficient electrical engines; usually magnetic engines. That use only the tiniest about of energy relative to common electric engines. But where is the government? Why aren't these technologies being supported and advanced?
So, not wanting to ramble too much, I think, someday, what we perceive as faster-than-light travel will certainly be possible, and it will be done, in a sense, by stepping out of the standard space-time continuum and stepping back in at a new distant location.
As another side note, while watching some physics lectures on YouTube, I discovered that there are bonded particles that act very similar to the way the philotic connection that make the ansibles work. What happens to one particle instantly happens to the other particle with no consideration for time or distance.
Perhaps that means the ansible really will someday exist as we see them in fiction.
Just a thought. Steve/bluewizard
Posts: 803 | Registered: May 2006
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quote:Originally posted by BlueWizard: As another side note, while watching some physics lectures on YouTube, I discovered that there are bonded particles that act very similar to the way the philotic connection that make the ansibles work. What happens to one particle instantly happens to the other particle with no consideration for time or distance.
Sort of, but not exactly, if you're referring to quantum entanglement. As I understand it, you can't actually transmit information using only entangled pairs. My understanding of entanglement is that when you measure the state of one particle in the pair, then the other pair will always be measured at the other state, even if the distance between the two states is so great that light could not reach from the first experiment to the second before the second is performed. So basically, if person A measures one entangled particle and gets a 0, then person B measuring the second particle will get a 1.
If I'm wrong about any of this, then I apologize and hope someone can come give a better explanation, but that is my understanding of what entanglement does. In other words, there isn't actually any way that we can see to use it to actually transmit information past light speed.
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I'm not an expert, but I have heard repeatedly that entanglement does not violate causality (that is, it does not allow information to go faster than light).
Posts: 15770 | Registered: Dec 2001
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That is true, yes. I'm about to say stuff that is extremely inaccurate, so grano salis. Suppose you have an ace of spades and an ace of hearts. You put each card in an envelope and mix them up. You mail one envelope to Alpha Centauri. When it has arrived, you open the envelope you kept. From the contents of your envelope, you instantly know the content of the envelope you sent away, without having to wait 4 years for light to travel! Yay! But as a means of communicating with Alpha Centauri, it leaves something to be desired.
Please note, all that was a lie-to-children. The real entanglement involves the collapse of quantum wave states and superpositions. In the analogy above, not only do you not know which card you sent to Alpha Centauri, the card doesn't know either. By opening your envelope, you cause a change in the card at Alpha Centauri: It now knows what suit it is, instantly, no lightspeed waiting. But that's still not helpful for communicating, because there's no way for you to say "I'm going to open my envelope in such a way that I get the ace of spades". If you could, ah, then you could ensure that Alpha Centauri got the ace of hearts, and you would have communication. But this cannot be done, or at any rate, until we know what the phenomenon we describe as "quantum wave collapse" is really doing, we have no way of even starting to theorise about how to do it.
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If we could travel at the speed of light, where would we go? We can already travel pretty darn fast, and yet we're all just sitting in front of computers - clearly there isn't all that much pressing to do out there.
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We can't travel very fast at all. Our practical sphere of travel is still very much bound by the time it would take -- generations upon generations to reach even the nearest star.
Traveling at faster than the speed of light would make it possible to travel elsewhere within a lifetime, a much more practical proposition.
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Why go to Alpha Centauri though, when we haven't even bothered to go to Mars? Some days I can't even be bothered to go to the grocery store. Thank goodness for PB&J sandwiches.
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Well, we'd no doubt send unmanned probes initially.
There are a couple reasons we might go to another place.
The big one is, a planet that could sustain human life without living entirely in space suits.
A secondary possibility would be something we're extremely interested in studying; unlike Mars, which is close enough to study remotely, something light years away could only be effectively studied in detail by humans.
And, of course, if travel faster than light speed were economical, it would make it much, much easier to get to Mars, so we'd probably go there, too.
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Just in case the question was serious... The reason we would want to travel elsewhere is so Humanity would not be at risk of destroying ourselves all at once (or even being destroyed by something else, though I find that less likely).
If we were spread out, then nuclear war on Earth would certainly suck, but it wouldn't be the end of our entire species.
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In the case at hand, I sent the envelope into outer space just to make it clear that I did not in fact have it up my sleeve, and also to make the lightspeed delay quite large.
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Let's say we actually achieve even just light speed travel. If i remember correctly, the nearest star is 800 light years away, so we still have nowhere to go. Just a thought. Posts: 1574 | Registered: May 2008
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You're neglecting relativistic effects. If we were traveling exactly at light speed (which won't happen), exactly no time would pass for the traveler.
Even if we could reach (without near certain death) a reasonable percentage of light speed, that would bring distant planets well into manageable lengths of flight for travelers.
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What I was thinking was that Earthside, technology would be so drastically changed. If a goverment unites all of earth 800 years later they might not control earth. Hmmmmmmmmmmmmm
Posts: 1574 | Registered: May 2008
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quote:Originally posted by fugu13: You're neglecting relativistic effects. If we were traveling exactly at light speed (which won't happen), exactly no time would pass for the traveler.
Even if we could reach (without near certain death) a reasonable percentage of light speed, that would bring distant planets well into manageable lengths of flight for travelers.
Mmm. You really want to be in the high nineties to see any appreciable relativistic effects.
Alpha Centauri, the nearest star, is 4.3 lightyears away.
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i think fugu13 was making a separate point, which is that at an appreciable fraction of light speed, we can get to nearby star systems within a relatively low number of years.
It takes a lot of energy, though. Accelerating a 2000kg probe to 10% the speed of light would take about as much energy as it takes to run 100 million 100w light bulbs for a year. (My math was probably not very accurate but is based mainly on the calculator here and 1 watt hour = 3600 joules.)
Posts: 4287 | Registered: Mar 2005
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Fugu what I mean is that the colonists would have no help, and modern day humans almost do nothing for themselves. (The people who could possibly afford to go into space) We be lazy. Posts: 1574 | Registered: May 2008
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