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DogWelder
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(06-24-2011, 11:55 PM)
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I found this explanation on reddit the other day about why FTL travel cannot exist, or rather, why "faster than light" is a meaningless statement. If you're interested in relativity or physics in general, it's a pretty cool read.

There are a lot of simple, intuitive explanations of this to be had out there … but I kind of hate them all. You might google around a bit and find discussion of something called "relativistic mass," and how it requires more force to accelerate an object that's already moving at a high velocity, stuff like that. That's a venerable way of interpreting the mathematics of special relativity, but I find it unnecessarily misleading, and confusing to the student who's just dipping her first toe into the ocean of modern physics. It makes the universe sound like a much different, and much less wonderful, place than it really is, and for that I kind of resent it.

When I talk about this subject, I do it in terms of the geometric interpretation that's consistent with general relativity. It's less straightforward, but it doesn't involve anything fundamentally more difficult than arrows on pieces of paper, and I think it offers a much better understanding of the universe we live in than hiding behind abstractions like "force" and outright falsehoods like "relativistic mass." Maybe it'll work for you, maybe it won't, but here it is in any case.

First, let's talk about directions, just to get ourselves oriented. "Downward" is a direction. It's defined as the direction in which things fall when you drop them. "Upward" is also a direction; it's the opposite of downward. If you have a compass handy, we can define additional directions: northward, southward, eastward and westward. These directions are all defined in terms of something — something that we in the business would call an "orthonormal basis" — but let's forget that right now. Let's pretend these six directions are absolute, because for what we're about to do, they might as well be.
I'm going to ask you now to imagine two more directions: futureward and pastward. You can't point in those directions, obviously, but it shouldn't be too hard for you to understand them intuitively. Futureward is the direction in which tomorrow lies; pastward is the direction in which yesterday lies.

These eight directions together — upward, downward, northward, southward, eastward, westward, pastward, futureward — describe the fundamental geometry of the universe. Each pair of directions we can call a "dimension," so the universe we live in is four-dimensional. Another term for this four-dimensional way of thinking about the universe is "spacetime." I'll try to avoid using that word whenever necessary, but if I slip up, just remember that in this context "spacetime" basically means "the universe."
So that's the stage. Now let's consider the players.

You, sitting there right now, are in motion. It doesn't feel like you're moving. It feels like you're at rest. But that's only because everything around you is also in motion. No, I'm not talking about the fact that the Earth is spinning or that our sun is moving through the galaxy and dragging us along with it. Those things are true, but we're ignoring that kind of stuff right now. The motion I'm referring to is motion in the futureward direction.
Imagine you're in a train car, and the shades are pulled over the windows. You can't see outside, and let's further imagine (just for sake of argument) that the rails are so flawless and the wheels so perfect that you can't feel it at all when the train is in motion. So just sitting there, you can't tell whether you're moving or not. If you looked out the window you could tell — you'd either see the landscape sitting still, or rolling past you. But with the shades drawn over the windows, that's not an option, so you really just can't tell whether or not you're in motion.

But there is one way to know, conclusively, whether you're moving. That's just to sit there patiently and wait. If the train's sitting at the station, nothing will happen. But if it's moving, then sooner or later you're going to arrive at the next station.

In this metaphor, the train car is everything that you can see around you in the universe — your house, your pet hedgehog Jeremy, the most distant stars in the sky, all of it. And the "next station" is tomorrow.

Just sitting there, it doesn't feel like you're moving. It feels like you're sitting still. But if you sit there and do nothing, you will inevitably arrive at tomorrow.
That's what it means to be in motion in the futureward direction. You, and everything around you, is currently moving in the futureward direction, toward tomorrow. You can't feel it, but if you just sit and wait for a bit, you'll know that it's true.

So far, I think this has all been pretty easy to visualize. A little challenging maybe; it might not be intuitive to think of time as a direction and yourself as moving through it. But I don't think any of this has been too difficult so far.

Well, that's about to change. Because I'm going to have to ask you to exercise your imagination a bit from this point on.

Imagine you're driving in your car when something terrible happens: the brakes fail. By a bizarre coincidence, at the exact same moment your throttle and gearshift lever both get stuck. You can neither speed up nor slow down. The only thing that works is the steering wheel. You can turn, changing your direction, but you can't change your speed at all.
Of course, the first thing you do is turn toward the softest thing you can see in an effort to stop the car. But let's ignore that right now. Let's just focus on the peculiar characteristics of your malfunctioning car. You can change your direction, but you cannot change your speed.

That's how it is to move through our universe. You've got a steering wheel, but no throttle. When you sit there at apparent rest, you're really careening toward the future at top speed. But when you get up to put the kettle on, you change your direction of motion through spacetime, but not your speed of motion through spacetime. So as you move through space a bit more quickly, you find yourself moving through time a bit more slowly.
You can visualize this by imagining a pair of axes drawn on a sheet of paper. The axis that runs up and down is the time axis, and the upward direction points toward the future. The horizontal axis represents space. We're only considering one dimension of space, because a piece of paper only has two dimensions total and we're all out, but just bear in mind that the basic idea applies to all three dimensions of space.

Draw an arrow starting at the origin, where the axes cross, pointing upward along the vertical axis. It doesn't matter how long the arrow is; just know that it can be only one length. This arrow, which right now points toward the future, represents a quantity physicists call four-velocity. It's your velocity through spacetime. Right now, it shows you not moving in space at all, so it's pointing straight in the futureward direction.

If you want to move through space — say, to the right along the horizontal axis — you need to change your four-velocity to include some horizontal component. That is, you need to rotate the arrow. But as you do, notice that the arrow now points less in the futureward direction — upward along the vertical axis — than it did before. You're now moving through space, as evidenced by the fact that your four-velocity now has a space component, but you have to give up some of your motion toward the future, since the four-velocity arrow can only rotate and never stretch or shrink.

This is the origin of the famous "time dilation" effect everybody talks about when they discuss special relativity. If you're moving through space, then you're not moving through time as fast as you would be if you were sitting still. Your clock will tick slower than the clock of a person who isn't moving.

This also explains why the phrase "faster than light" has no meaning in our universe. See, what happens if you want to move through space as fast as possible? Well, obviously you rotate the arrow — your four-velocity — until it points straight along the horizontal axis. But wait. The arrow cannot stretch, remember. It can only rotate. So you've increased your velocity through space as far as it can go. There's no way to go faster through space. There's no rotation you can apply to that arrow to make it point more in the horizontal direction. It's pointing as horizontally as it can. It isn't even really meaningful to think about something as being "more horizontal than horizontal." Viewed in this light, the whole idea seems rather silly. Either the arrow points straight to the right or it doesn't, and once it does, it can't be made to point any straighter. It's as straight as it can ever be.
That's why nothing in our universe can go faster than light. Because the phrase "faster than light," in our universe, is exactly equivalent to the phrase "straighter than straight," or "more horizontal than horizontal." It doesn't mean anything.

Now, there are some mysteries here. Why can four-velocity vectors only rotate, and never stretch or shrink? There is an answer to that question, and it has to do with the invariance of the speed of light. But I've rambled on quite enough here, and so I think we'll save that for another time. For right now, if you just believe that four-velocities can never stretch or shrink because that's just the way it is, then you'll only be slightly less informed on the subject than the most brilliant physicists who've ever lived.

EDIT: There's some discussion below that goes into greater detail about the geometry of spacetime. The simplified model I described here talked of circles and Euclidean rotations. In real life, the geometry of spacetime is Minkowskian, and rotations are hyperbolic. I chose to gloss over that detail so as not to make a challenging concept even harder to visualize, but as others have pointed out, I may have done a disservice by failing to mention what I was simplifying. Please read the follow-ups.

Source: http://www.reddit.com/r/askscience/c...han_the_speed/

Well in a sense the poster doesn't really explain why FTL travel cannot exist, merely that light travels as fast as it can within the limits of the universe. The limit in the above example being the length of the arrow. Why that limit exists is a totally different question and as of now no-one knows the answer.
TacticalFox88
Lives in a Tom Clancy novel
(06-25-2011, 12:03 AM)
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If only we could bend the laws of Physics to our whim.
The Lamp
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(06-25-2011, 12:05 AM)
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I was hoping for drawings and pictures >:(

I guess I'll read.
DeathIsTheEnd
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(06-25-2011, 12:09 AM)
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There is one thing that possibly does. Bad news.

I think 'why does E=mc2?' gives a pretty good explanation.
tino
Banned
(06-25-2011, 12:10 AM)
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That's too long to be called "easy to understand".

How about you quote a comic or something?
DrForester
Kills Photobucket
(06-25-2011, 12:11 AM)
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Then why we still got Star Treks?
Escape Goat
(06-25-2011, 12:11 AM)

Originally Posted by DrForester

Then why we still got Star Treks?


why we still got airplanes
StuBurns
just talking loud
and saying nothing
(06-25-2011, 12:12 AM)
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That's not an easy explanation.

The train scene in Dumbo is an easy explanation.

As something gets faster, it gets heavier, as it gets heavier it gets harder to move. The closer you get to light speed the harder it is to have the power needed to push the increasing mass.

Done.
MRORANGE
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(06-25-2011, 12:12 AM)
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I was hoping you would have created a drawing in paint for us :|
Guevara
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(06-25-2011, 12:12 AM)
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Nation Shudders At Large Block Of Uninterrupted Text


The giant mass of prose was devoid of so much as a large pulled quote for readers to glance at before moving on.

WASHINGTON—Unable to rest their eyes on a colorful photograph or boldface heading that could be easily skimmed and forgotten about, Americans collectively recoiled Monday when confronted with a solid block of uninterrupted text.

Dumbfounded citizens from Maine to California gazed helplessly at the frightening chunk of print, unsure of what to do next. Without an illustration, chart, or embedded YouTube video to ease them in, millions were frozen in place, terrified by the sight of one long, unbroken string of English words.

"Why won't it just tell me what it's about?" said Boston resident Charlyne Thomson, who was bombarded with the overwhelming mass of black text late Monday afternoon. "There are no bullet points, no highlighted parts. I've looked everywhere—there's nothing here but words."

- The Onion
Zzoram
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(06-25-2011, 12:12 AM)
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Most sci-fi suggests warping space to move faster than light, not actually moving faster than light, but basically making a shortcut through space.
Stinkles
Banned
(06-25-2011, 12:13 AM)
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Originally Posted by Teh Hamburglar

why we still got airplanes

Why we still got magnets?
OliveJuice
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(06-25-2011, 12:14 AM)
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I like:

It would take an infinite amount of energy to accelerate an object with mass to the speed of light

Simple and straight to the point.
Always-honest
always-end-with-a-swirl
(06-25-2011, 12:15 AM)
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Is there a three picture version? Cause i'm drunk and it's hard to read.
Sharp
Member
(06-25-2011, 12:15 AM)
This is a fucking amazing explanation. Much more intuitive than the traditional one. I urge you all to plow through it--you will then be able to tell your friends you understand general relativity.

Edit: Damn it, you lazy bums. Okay. Basically, time is another direction, and we're always moving at the same speed through time when we're perfectly still... but when we start moving in space, we're still moving at the same speed--just in a different "direction." So traveling faster than light makes no sense.
StuBurns
just talking loud
and saying nothing
(06-25-2011, 12:15 AM)
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Originally Posted by OliveJuice

I like:

Simple and straight to the point.

Even better.
TheChewyWaffles
Member
(06-25-2011, 12:15 AM)
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Sorry, but I was expecting a sentence or two, tops. A wall of text is not an "easy to understand" explanation.
Escape Goat
(06-25-2011, 12:16 AM)

Originally Posted by OuterWorldVoice

Why we still got magnets?

its a billion dollar industry man!
DarkKyo
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(06-25-2011, 12:17 AM)
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Without reading that article, I thought that the contents of the universe are moving away from each other at speeds faster than the speed of light. That's why we can't see outside of the observable universe, because all of that stuff out there is moving away from us at a rate faster than the light can travel to us.
Sharp
Member
(06-25-2011, 12:17 AM)

Originally Posted by BigNastyCurve

Sorry, but I was expecting a sentence or two, tops. A wall of text is not an "easy to understand" explanation.

It might suck, but sometimes fundamental facts about the universe aren't going to boil down to "a sentence or two, tops" and still be easy to understand.
DogWelder
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(06-25-2011, 12:18 AM)
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Originally Posted by DrForester

Then why we still got Star Treks?

Well I never watched Star Trek but hypothetically, if you could bend space in such a way that it is contracted ahead of your spaceship and expanded behind (a "bubble" which envelops the ship), it could reach its destination faster than it would take light outside of that bubble. This is because you are essentially shortening the distance between the ship and it's destination, but you are not actually travelling faster than light. Light within your hypothetical bubble would still travel faster than your spacecraft.
Zzoram
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(06-25-2011, 12:20 AM)
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Originally Posted by esc

Well I never watched Star Trek but hypothetically, if you could bend space in such a way that it is contracted ahead of your spaceship and expanded behind (a "bubble" which envelops the ship), it could reach its destination faster than it would take light outside of that bubble. This is because you are essentially shortening the distance between the ship and it's destination, but you are not actually travelling faster than light. Light within your hypothetical bubble would still travel faster than your spacecraft.

That's basically what warp drives do in Star Trek.
tearsofash
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(06-25-2011, 12:20 AM)
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Yeah, well then how does light go so fast?

Larrycableguy.gif

I honestly don't care much about FTL. Light-speed would be good enough.
StuBurns
just talking loud
and saying nothing
(06-25-2011, 12:20 AM)
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Originally Posted by Dechaios

Without reading that article, I thought that the contents of the universe are moving away from each other at speeds faster than the speed of light. That's why we can't see outside of the observable universe, because all of that stuff out there is moving away from us at a rate faster than the light can travel to us.

Nop. The 'observable universe' is for practicalities sake, the universe. How far it's gotten so far.
DogWelder
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(06-25-2011, 12:20 AM)
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Originally Posted by OliveJuice

I like:



Simple and straight to the point.

Simple in what way? It is a statement of fact, it does not not explain anything to the lay man. And it certainly does not explain that light speed is dictated by the physical laws of the Universe and that we are all moving through spacetime at c.
I'd like to add to this that your explanation also does not say anything about time dilation, length contraction and how light does not move through the dimension we call time because of its speed. Those are what I found to be the most interesting parts of the explanation (although I did have some bg knowledge of them beforehand).
Last edited by DogWelder; 06-25-2011 at 12:24 AM.
Kyaw
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(06-25-2011, 12:21 AM)
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The part with the axis and the graph and the four velocity vector thing confused me because it's midnight and i'm tired. I'll have a read through again tomorrow.

Interesting stuff but not an easy explanation by any means.
TacticalFox88
Lives in a Tom Clancy novel
(06-25-2011, 12:22 AM)
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What about wormholes? Open up a rift in space, it takes you to another part of space. No laws of Physics broken....I think?
StuBurns
just talking loud
and saying nothing
(06-25-2011, 12:23 AM)
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Originally Posted by esc

Simple in what way? It is a statement of fact, it does not not explain anything to the lay man. And it certainly does not explain that light speed is dictated by the physical laws of the Universe and that we are all moving through spacetime at c.

It explains it perfectly. The only thing it requires from the lay man is that as something moves it gets heavier, and everyone knows that, if not implicitly.

Originally Posted by TacticalFox88

What about wormholes? Open up a rift in space, it takes you to another part of space. No laws of Physics broken....I think?

You don't move faster than light in a wormhole, you just travel a shorter distance.
weekend_warrior
Banned
(06-25-2011, 12:23 AM)
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Originally Posted by Sharp

This is a fucking amazing explanation. Much more intuitive than the traditional one. I urge you all to plow through it--you will then be able to tell your friends you understand general relativity.

Edit: Damn it, you lazy bums. Okay. Basically, time is another direction, and we're always moving at the same speed through time when we're perfectly still... but when we start moving in space, we're still moving at the same speed--just in a different "direction." So traveling faster than light makes no sense.

What does time direction have to do with faster then light travel?

The simplest explanation is that the more mass something has the more energy it takes to move it and nothing has less mass then light.
Zzoram
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(06-25-2011, 12:24 AM)
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Originally Posted by TacticalFox88

What about wormholes? Open up a rift in space, it takes you to another part of space. No laws of Physics broken....I think?

Except it's never been demonstrated that creating these folds in space to create short cuts is actually plausible.
Marty Chinn
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(06-25-2011, 12:25 AM)
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Originally Posted by Sharp

This is a fucking amazing explanation. Much more intuitive than the traditional one. I urge you all to plow through it--you will then be able to tell your friends you understand general relativity.

Edit: Damn it, you lazy bums. Okay. Basically, time is another direction, and we're always moving at the same speed through time when we're perfectly still... but when we start moving in space, we're still moving at the same speed--just in a different "direction." So traveling faster than light makes no sense.

The problem here is you're not connecting time to light and explaining how and why they are connected. You're pretty much saying here's a bunch of stuff, thus here's a cookie.
Mr. Tone
Member
(06-25-2011, 12:26 AM)

Originally Posted by Sharp

This is a fucking amazing explanation. Much more intuitive than the traditional one. I urge you all to plow through it--you will then be able to tell your friends you understand general relativity.

Special relativity.
Sharp
Member
(06-25-2011, 12:29 AM)

Originally Posted by Marty Chinn

The problem here is you're not connecting time to light and explaining how and why they are connected. You're pretty much saying here's a bunch of stuff, thus here's a cookie.

Well, the length of the vector happens to be the speed of light, but the point is that it's unchanging.

Originally Posted by weekend_warrior

What does time direction have to do with faster then light travel?

The simplest explanation is that the more mass something has the more energy it takes to move it and nothing has less mass then light.

Then people will just speculate about things with "negative mass" or something stupid like that (though IIRC the equation would require it to have imaginary mass).
Mudkips
Banned
(06-25-2011, 12:32 AM)
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That's not an easy to understand explanation, nor is it even an explanation.

Speed is change in position over change in time.
The speed of light is the maximum single-step change in position over the minimum single-step change in time.

However, space and time are one and the same. Thus, "speed" as we usually think of it is merely a comparison between the change in 3 dimensions (space) of the universe, and a change in the other dimension (time). If you consider travel in all 4 dimensions, then your "speed" is merely the size of that vector.

A body with a specific energy can never change the magnitude of its vector. And Einstein's famous E=MC^2 states that a body's energy is inextricably linked to its mass. Thus, for you to be able to change the magnitude of your 4-dimensional vector, you would have to gain energy, and thus gain mass.

And if you were gaining mass somehow, you would also need to speed up the mass you gained. Thus, your mass would have to be infinite to exceed the speed of light.


No one knows why the size of our 4 dimensional vector is what it is. It could be related to some fundamental property of spacetime (such as the smallest amount of distance or time possible).

Originally Posted by DeathIsTheEnd

There is one thing that possibly does.

Uh, no?
Chichikov
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(06-25-2011, 12:33 AM)
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That's not really an explanation, and in any case, the concepts he describes already rely on his conclusion, so that's kinda circular.

But it's a very nice introduction to Minkowski's space.
DogWelder
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(06-25-2011, 12:33 AM)
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Originally Posted by StuBurns

It explains it perfectly. The only thing it requires from the lay man is that as something moves it gets heavier, and everyone knows that, if not implicitly.

A superficial understanding is not an understanding. Just because someone can answer the question in the title with a brief statement of fact does not mean they understand the underlying principles. I'm not saying it's not an appropriate answer to the question, but you're looking at the topic title too literally. It's not just about FTL travel, but about spacetime and the Universe as well.
Dibbz
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(06-25-2011, 12:34 AM)
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Originally Posted by Dechaios

Without reading that article, I thought that the contents of the universe are moving away from each other at speeds faster than the speed of light. That's why we can't see outside of the observable universe, because all of that stuff out there is moving away from us at a rate faster than the light can travel to us.

This confuses me. If light is emitted from stars then they should not be constrained to the object from which they emitted right? So the light from them would eventually reach us wouldn't it?
DogWelder
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(06-25-2011, 12:34 AM)
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Originally Posted by Chichikov

That's not really an explanation, and in any case, the concepts he describes already rely on his conclusion, so that's kinda circular.

Well I did point that out in the OP. Dammit, I knew the title was going to cause a ruckus. It's my own fault.
Averon
Member
(06-25-2011, 12:35 AM)

Originally Posted by esc

Well I never watched Star Trek but hypothetically, if you could bend space in such a way that it is contracted ahead of your spaceship and expanded behind (a "bubble" which envelops the ship), it could reach its destination faster than it would take light outside of that bubble. This is because you are essentially shortening the distance between the ship and it's destination, but you are not actually travelling faster than light. Light within your hypothetical bubble would still travel faster than your spacecraft.


Isn't that what the Alcubierre drive does?
Void Insanity
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(06-25-2011, 12:36 AM)
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Even if FTL is not possible why is it of any concern of ours? It'll never happen in our lifetimes even if it is possible.
Chichikov
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(06-25-2011, 12:37 AM)
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Originally Posted by esc

Well I did point that out in the OP. Dammit, I knew the title was going to cause a ruckus. It's my own fault.

The problem is that you put text above and below a giant wall of text.
I only read the part above it.

I think you greatly overestimate GAF's willingness to read stuff before submitting a reply.
DarkKyo
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(06-25-2011, 12:37 AM)
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Originally Posted by StuBurns

Nop. The 'observable universe' is for practicalities sake, the universe. How far it's gotten so far.

...the observable universe consists of the galaxies and other matter that we can in principle observe from Earth in the present day, because light (or other signals) from those objects has had time to reach us since the beginning of the cosmological expansion...
http://en.wikipedia.org/wiki/Observable_universe

There is stuff in the universe that we can't see because the light hasn't gotten to us. The universe is expanding, sure, but there is a limit to how much we can see because the light hasn't reached us yet. So there is more out there that we haven't been able to observe. I think what I was referring to earlier is that given enough time, the acceleration of all matter in the universe will become faster than the speed of light, and so galaxies will just fade out into the void of space due to the light's inability to ever reach us. Everything will be so far apart, you wouldn't be able to see any stars outside of your own galaxy.
weekend_warrior
Banned
(06-25-2011, 12:37 AM)
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Ok I read it and it seems completely stupid to me. He basically says you can't travel faster then time because time has a max speed and were always going it.
DogWelder
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(06-25-2011, 12:38 AM)
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Originally Posted by Mudkips

That's not an easy to understand explanation, nor is it even an explanation.

Speed is change in position over change in time.
The speed of light is the maximum single-step change in position over the minimum single-step change in time.

However, space and time are one and the same. Thus, "speed" as we usually think of it is merely a comparison between the change in 3 dimensions (space) of the universe, and a change in the other dimension (time). If you consider travel in all 4 dimensions, then your "speed" is merely the size of that vector.

A body with a specific energy can never change the magnitude of its vector. And Einstein's famous E=MC^2 states that a body's energy is inextricably linked to its mass. Thus, for you to be able to change the magnitude of your 4-dimensional vector, you would have to gain energy, and thus gain mass.

And if you were gaining mass somehow, you would also need to speed up the mass you gained. Thus, your mass would have to be infinite to exceed the speed of light.


No one knows why the size of our 4 dimensional vector is what it is. It could be related to some fundamental property of spacetime (such as the smallest amount of distance or time possible).



Uh, no?

Yours is not an explanation either. In fact, you pretty much stated exactly what was stated by the author in the OP in more technical terms and then concluded with "no-one knows why the size of our 4-dimensional vector is what it is" which was also the conclusion made in the OP. How is your explanation easier to understand exactly?


Originally Posted by Chichikov

The problem is that you put text above and below a giant wall of text.
I only read the part above it.

I think you greatly overestimate GAF's willingness to read stuff before submitting a reply.

Yeah probably. Oh well.
Haly
One day I realized that sadness is just another word for not enough coffee.
(06-25-2011, 12:38 AM)
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Wait, is this vector rotation thing an analogy or what?
OliveJuice
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(06-25-2011, 12:38 AM)
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Originally Posted by esc

Simple in what way? It is a statement of fact, it does not not explain anything to the lay man. And it certainly does not explain that light speed is dictated by the physical laws of the Universe and that we are all moving through spacetime at c.
I'd like to add to this that your explanation also does not say anything about time dilation, length contraction and how light does not move through the dimension we call time because of its speed. Those are what I found to be the most interesting parts of the explanation (although I did have some bg knowledge of them beforehand).

What you actually wanted was an easy to understand explanation of how we understand our universe through general relativity, which the simple explanation you posted takes about 10 paragraphs (at least half the article) to go through.

I was giving the most simple and direct answer to the title of the thread: Why nothing can travel faster than light.

I personally think it is a simple explanation, since laymans (who?) know that any object that moves requires energy.
DeathIsTheEnd
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(06-25-2011, 12:39 AM)
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Originally Posted by Mudkips

Uh, no?

It's from Hitch Hikers Guide to the Galaxy.

Nothing travels faster than the speed of light with the possible exception of bad news, which obeys its own special laws.

Funnily enough, I know it's not true.
Zzoram
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(06-25-2011, 12:39 AM)
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Originally Posted by Void Insanity

Even if FTL is not possible why is it of any concern of ours? It'll never happen in our lifetimes even if it is possible.

Because I have an interest in the future of humanity, particularly if we'll be able to spread across the stars to ensure our species (or whatever our progency evolve into) never goes extinct, or if we'll go extinct on our home planet.

If we are the only intelligent life in the universe, I want to make sure intelligent life never goes extinct by spreading out so we don't have all our eggs in one basket.
makingmusic476
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(06-25-2011, 12:40 AM)
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I don't get how that's simple.

He basically took 20 paragraphs to say "Light is already moving as fast as it physically can, thus it would be impossible to move anything faster."

Which he kinda sums up in these two paragraphs near the end:

This also explains why the phrase "faster than light" has no meaning in our universe. See, what happens if you want to move through space as fast as possible? Well, obviously you rotate the arrow — your four-velocity — until it points straight along the horizontal axis. But wait. The arrow cannot stretch, remember. It can only rotate. So you've increased your velocity through space as far as it can go. There's no way to go faster through space. There's no rotation you can apply to that arrow to make it point more in the horizontal direction. It's pointing as horizontally as it can. It isn't even really meaningful to think about something as being "more horizontal than horizontal." Viewed in this light, the whole idea seems rather silly. Either the arrow points straight to the right or it doesn't, and once it does, it can't be made to point any straighter. It's as straight as it can ever be.
That's why nothing in our universe can go faster than light. Because the phrase "faster than light," in our universe, is exactly equivalent to the phrase "straighter than straight," or "more horizontal than horizontal." It doesn't mean anything.

DogWelder
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(06-25-2011, 12:41 AM)
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Originally Posted by OliveJuice

What you actually wanted was an easy to understand explanation of how we understand our universe through general relativity, which the simple explanation you posted takes about 10 paragraphs (at least half the article) to go through.

I was giving the most simple and direct answer to the title of the thread: Why nothing can travel faster than light.

I personally think it is a simple explanation, since laymans (who?) know that any object that moves requires energy.

The title is a simplification and a mistake on my part. My bad.

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