Laymen's Terms, please

[Itisnotlogical]

Sure, I may be a dumb kid (I'm sure as hell not a scientist, like I'm sure some people here are), but can anyone explain exactly why we can't go faster than light in simple terms? Because I've always heard people say "Oh, it's impossible", "It will never happen in a trillion billion million years" so on and so forth, and I've never really understood why it would be so impossible. Once again, I'm no scientist, so forgive me if I'm a bit ignorant, but it seems to me just a simple problem of:

A. Generating enough speed to get going faster than light, and
B. Finding a way to navigate safely at such a high speed.

So, can anyone explain why such a thing would be so impossible? Not generating any sort of field or going through wormholes, just plain accelerating until you reach faster-than-light speeds.

 

[STR]

Because the energy you need to accelerate to the speed of light is an exponential curve. I'm going to pull numbers from my ass here to exemplify. Say to get to 1/2 the speed of light you need 1x power (this is a generic unit I made up as well). To get to 90% you need 2x. 95% needs 10x. 99% needs 100x. 99.9 needs 10,000x. 99.99%? 100,000,000x. The closer you get to 100%, the greater the increase in power, the result is that you basically need infinite power to reach the speed of light, and almost infinite power to get even close.

So since it takes more energy than exists in the entire universe to get to the speed of light, there's no way to go beyond it without the fancy gimmicks you mention. Navigating actually isn't too much of a problem. You point the ship at your target, then accelerate. Space is, for all intents, empty so the odds of you running into anything is practically zero.

 

[Shaw]

Okay, well, lets look at this for second in the way Einstein did more than a century ago. You are sitting at your computer and you have a flash light. You point the flash light in some direction and measure the speed of the light in the beam. And no surprise, you find that the light is moving at the speed of light.

But then you ask yourself the hard question... while it seems like you are not moving, you are on the Earth, which is spinning and orbiting the Sun, and the Sun is orbiting the Milky Way... you quickly realize that you are very far from sitting still. In all actuality, you are moving at a very high rate of speed.

But then you remember that you just did an experiment that showed that the speed of a beam of light from your flash light (which is moving right along with you) was moving at the speed of light... no matter which direction you pointed the beam.

As it turns out, no matter where you go, no matter how fast you are moving, a beam of light will always seem to be moving at the speed of light relative to you.

But here is the kicker... someone else, moving at a different speed in a different direction would also measure the speed of your beam of light from your flash light as the speed of light.

So what happens as you get close to moving at the speed of light?

Do the experiment again, and you find that the beam from the flash light you have kept with you is still moving at the speed of light relative to you. What has happened is that time has slowed down (for you) and distances in the direction of your travel have shrunk so that the speed of light doesn't change for you.

Why is this needed/important?

The problem is that there is no universal reference frame. That is, there is no zero velocity spot in the universe by which the rest of the universe can determine how fast it is moving. As it turns out, rather than a zero velocity as a constant, we use the speed of light as the universal reference. There is nothing (and no place) that is not moving relative to something else, but for all reference frames (everywhere) the speed of light is the same.

So in our universe, how would you know if you reached the speed of light?

As you get closer and closer, you shrink in that direction and time passes slower and slower (so that a beam of light will still seem like it is moving at the speed of light relative to you). Other things happen too (your mass increases), but you never reach the speed of light because time (for you) ground to a halt.

You wouldn't notice any of that happening to you, but your friends watching you would see all that happen... and then go on with their lives.


If you don't get this, don't feel bad. We are used to nice, fixed coordinate grids when we think of space/geometry, and the fact that nothing like that nice environment exists in the actual universe make it a little disorienting for most everyone.

 

[SPCTRE]

you basically need infinite power to reach the speed of light, and almost infinite power to get even close

Or, in other words: To accelerate an object (if the object's mass is > 0) to lightspeed would require infinite time with any finite acceleration, or infinite acceleration for a finite amount of time.

Not sure if that rephrasing helps

Another problem with FTL has to do with Albert Einstein's theory of relativity - in essence, according to his theory of special relativity, FTL travel = time travel, and as we have seen in Star Trek on numerous occasions, time travel is a very problematic concept - some would even call it impossible

Edit: Never mind, I see Shaw already did a great job of explaining the main Einsteinian argument against FTL travel

 

[Myasishchev]

Because the energy you need to accelerate to the speed of light is an exponential curve. I'm going to pull numbers from my ass here to exemplify. Say to get to 1/2 the speed of light you need 1x power (this is a generic unit I made up as well). To get to 90% you need 2x. 95% needs 10x. 99% needs 100x. 99.9 needs 10,000x. 99.99%? 100,000,000x. The closer you get to 100%, the greater the increase in power, the result is that you basically need infinite power to reach the speed of light, and almost infinite power to get even close.

So since it takes more energy than exists in the entire universe to get to the speed of light, there's no way to go beyond it without the fancy gimmicks you mention. Navigating actually isn't too much of a problem. You point the ship at your target, then accelerate. Space is, for all intents, empty so the odds of you running into anything is practically zero.

At severely high relativistic speeds, CBR and pinpoint sources like stars will blueshift toward UV, X, and gamma rays. Instellar hydrogen is also a problem at such speeds, since it will impact in much the same way as cosmic rays do the upper atmosphere; from this it is assumed that near-light speed travel will turn human beings stretchy, invisible, inflammable, or unattractively sclerotic.

 

[YellowSubmarine]

Problem 1: A velocity faster than light is impossible due to special relativity.

The faster you go, the more energy is required to make you go faster, to actually reach the speed of light you need infinite energy. At the speed of light the kinetic energy of your spacecraft will be infinite, and its relativistic mass will also be infinite. Formula for mass. Formula for energy

Consider time dilation. The faster you go, the more time slows down for you. Let's say we're at the point where it's twice slower. If you throw an apple at 20 km/h, an outside observer would see the apple flying at only 10 km/h relatively to you. For them twice the time passes until your apple reaches its destination. The same is true for your engines. They now require twice the energy to accelerate you to a given velocity.


Loophole: You can go from a point to point faster than light while maintaining a sublight velocity in space. You can either go through a wormhole which acts as a shortcut between two distant points, or you can use warp drive where space itself moves dragging you across the galaxy at superlight speeds while your velocity is zero.

Problem 2: Faster than light travel violates causality. It is accepted among physicists that the cause should precede the effect. However, if you could move to a certain point faster than light, you might create a situation where the cause is after the effect for some observer, or even experience actual time travel.

Consider the thought experiment with the train and two lightnings (video).

A person standing by a railway sees a train pass him by, and two lightning strikes hitting the front and the end of the train at exactly the same time. For a person sitting in the train, the front lightning will be seen first, because the train moves him towards it – he'll have moved slightly forward from his position until the light from the lightnings reach it. Now, imagine that they are no lightnings, but non-corporal lifeforms, talking through subspace and having insanely fast reactions. And consider that just before it hits, the back lightning sees a problem with the rail and warns the front lightning, which avoids it. From the person in the train, the cause will be after the effect, and relativity says that this is the order in which they happened. Time travel.

A better example is the tachyon pistol thought experiment, but it's too complicated to understand.

Loophole: Scrap global causality, and only keep local causality, or time travel is teh real OMFG LOL

Problem 3: I believe that any time travel, faster than light travel, or causality violations might also violate the second law of thermodynamics. I have never seen any documents asserting this before, but a quick search finds at least several persons claiming that the second law implies causality. In other words, something tells me that you can create a system of wormholes that allows you to use the same energy over and over fixing your energy needs without the need to harvest new energy.

Loophole: Like causality, consider that the law applies only locally. Oh, and the law only applies to the mechanical systems that we currently know about. A system that has a wormhole in it isn't one of them.

The energy problem: Any method of faster than light travel that has been proposed is expected to require an enormous amount of energy. For example, the energy required to curve the space in a way to across the galaxy with Alcubierre drive is more than the total energy in the universe. And on the top of it, both it and the wormholes are likely to require some kind of exotic matter that isn't known to exist so far.

Oh well, if they indeed require enormous energy, it might at least take care of the problem with the second law.

 

[diankra]

The major difference between physics as we best understand it now and science fiction is that:
Popular SF tends to treat travelling faster than light as doable - OK, you need some way round Einstein, but it's just going a bit faster isn't it?
On the other hand, time travel must be difficult - just look at all the problems it opens up.
That's a very common sense view... and common sense works very well in our common situations. But once you get out of our native environment, common sense is generally wrong. In this case, it means that FTL is potentially possible - but you need workable time travel to be able to do it.

 

[STR]

Because the energy you need to accelerate to the speed of light is an exponential curve. I'm going to pull numbers from my ass here to exemplify. Say to get to 1/2 the speed of light you need 1x power (this is a generic unit I made up as well). To get to 90% you need 2x. 95% needs 10x. 99% needs 100x. 99.9 needs 10,000x. 99.99%? 100,000,000x. The closer you get to 100%, the greater the increase in power, the result is that you basically need infinite power to reach the speed of light, and almost infinite power to get even close.

So since it takes more energy than exists in the entire universe to get to the speed of light, there's no way to go beyond it without the fancy gimmicks you mention. Navigating actually isn't too much of a problem. You point the ship at your target, then accelerate. Space is, for all intents, empty so the odds of you running into anything is practically zero.

At severely high relativistic speeds, CBR and pinpoint sources like stars will blueshift toward UV, X, and gamma rays. Instellar hydrogen is also a problem at such speeds, since it will impact in much the same way as cosmic rays do the upper atmosphere; from this it is assumed that near-light speed travel will turn human beings stretchy, invisible, inflammable, or unattractively sclerotic.

Yeah, but you really can't navigate around that.

 

[Silvercrest]

At severely high relativistic speeds, CBR and pinpoint sources like stars will blueshift toward UV, X, and gamma rays. Instellar hydrogen is also a problem at such speeds, since it will impact in much the same way as cosmic rays do the upper atmosphere; from this it is assumed that near-light speed travel will turn human beings stretchy, invisible, inflammable, or unattractively sclerotic.

The OP requested layman's terms, but you seem to be using some pretty fantastic language there.

 

[STR]

^Plus, it's the physics equivalent of saying "watch out for water while navigating your boat."

 

[RoJoHen]

How did we even discover the speed of light (if it's really as fast as it is, how are we even able to measure it?), and how do we know that nothing in the universe is faster?

I personally can't wrap my head around Relativity, especially the part where time slows down and our mass changes as we approach light speed. I just don't get it.

 

[Corwwyn]

time travel is a very problematic concept - some would even call it impossible

I would call it impossible.

 

[SPCTRE]

time travel is a very problematic concept - some would even call it impossible

I would call it impossible.

So would the Vulcan Science Academy - pardon my ENT reference

How did we even discover the speed of light (if it's really as fast as it is, how are we even able to measure it?), and how do we know that nothing in the universe is faster?

I personally can't wrap my head around Relativity, especially the part where time slows down and our mass changes as we approach light speed. I just don't get it.

Wikipedia has a decent article on Ole Rømer's determination of c. Pretty impressive how close he came to the actual value - and as early as 1676!

 

[Silvercrest]

How did we even discover the speed of light (if it's really as fast as it is, how are we even able to measure it?), and how do we know that nothing in the universe is faster?

The rules don't say that nothing is faster. There are hypothetical particles which move faster than light. The rules just say that nothing moving slower than light can be accelerated up to or beyond light speed. For reasons aforementioned.

I personally can't wrap my head around Relativity, especially the part where time slows down and our mass changes as we approach light speed. I just don't get it

Here's a super-simplified explanation which some of the physicists here probably won't like. If you're moving and look at an object, it will appear to be moving at a certain speed relative to you-- "a" miles per hour. If you move at a different speed and look at the same object, it will now appear to be moving at "b" miles per hour. Your relative speeds will change.

Light isn't like that. With respect to you, it will always appear to be moving at the same speed-- "c" miles per hour, no matter how fast you move. So it isn't relative-- it's fixed. And the only way that can be is if the elements that define speed ("miles" and "hours") become relative instead. "Hours", at least, get stretched or compressed accordingly.

 

[Shaw]

How did we even discover the speed of light (if it's really as fast as it is, how are we even able to measure it?), and how do we know that nothing in the universe is faster?

I personally can't wrap my head around Relativity, especially the part where time slows down and our mass changes as we approach light speed. I just don't get it.

I can give you the general story as I recall it from my studies...

The first time that the speed of light became a stumbling point was in James Clark Maxwell's elegant unification of electricity and magnetism. While quite beautiful, simple and powerful, much of the physics community were distrustful of Maxwell's Equations in the later half of the 19th century because they were dependent on the speed of light being a constant... everywhere and in all frames of reference.

At the time it was widely believed that light propagated through a medium called the ether, and that we could find out how fast the Earth/Sun were moving through this ether if we had instruments accurate enough to detect the small changes in the speed of light.

Well, the ability to do just such an experiment came shortly before the turn of the century (between the 19th and 20th centuries) in the form of the Michelson–Morley experiment. It was intended to see which direction the speed of light was slower (thought to be the general direction of travel through the ether)... but it detected nothing. No difference in the speed of light no matter which direction one measured it.

As I recall, a mathematician named Lorentz (who was one of Einstein's professors) came up with a mathematical construct to explain what was happening in the Michelson–Morley experiment now known as the Lorentz transformations. But he stopped short of asserting it beyond this one case.

Einstein, who was also a big fan of Maxwell's Equations, took Lorentz's work a step further in his Special Theory of Relativity. The Special in the name is there because the theory actually deals with a sort of unrealistic scenario... objects moving at constant velocities (no acceleration). In the real world everything in motion is actually undergoing some form of acceleration.

The acceleration issue and the fact that Special Relativity had set a limit on the speed of anything (which seemed to contradict Newton's equations for gravity) is what set Einstein in motion to figure out how this would work in general cases... a General Theory of Relativity.

What is truly amazing is that Einstein saw (thanks to his understanding of acceleration) what was happening long before the mathematics of General Relativity were in place. He was able to deduce what was happening with gravity by using thought experiments... and then the math followed a few years later.

That is generally how all this came about... but without going into too much detail. I think understanding Einstein's thought experiments (for both Special and General Relativity) are nearly as important as understanding the mathematics of them.

 

[The Borg Queen]

How fast can you run?

Why can't you run faster than that?

 

[Rett Mikhal]

Here it is in Laymen's terms.

Light always moves at the same speed. Always.

When you are standing still, it is going the normal speed.

When you are going mach 20, it is going the normal speed.

When you are going 1/2 of its speed, it is going the normal speed.

When you are going .9999999999 of its speed, it is going the normal speed.

Since the space part doesn't change, time has to change. Two people moving at different speeds will see light going the same speed because time slows down as you approach the speed of light. It's scientific fact.

So to go .99999999 of the speed of light would dilate time to the point an hour's worth of travel would be millions of years to everyone going no where close to that speed. Plus, it would take you thousands of years to get to another star system at that speed, regardless, so trillions of years would have passed and then at that point, the entire universe has ended.

Beyond lightspeed... has yet to be seen in terms of time dilation.

Here's a nifty video that explains it!

http://www.youtube.com/watch?v=V7vpw4AH8QQ

 

[sojourner]

Always. Except when they slow it down in a lab.

 

[Robert Maxwell]

Light always moves at the same velocity in a vacuum. That's the important part. Passing through any kind of medium will slow light down. It's the speed of light in a vacuum that is the absolute speed limit of the universe.

 

[Chaos Descending]

Layman's Terms:

Energy and mass are equivalent.

All of the mass-energy in a object depends on how much it has due to its, well, mass, and how much it has due to how fast it's going.

To speed something up from one speed to the next higher speed takes an amount of energy that is dependent upon the mass of the object.

Now remember, the mass-energy of an object depends on it's rest mass and the speed it's traveling, so the faster something is going, the more mass-energy it has. Therefore for each little bit faster you want to make something go, it takes greater and greater amounts of energy to make it go that small little bit faster, which then increases its speed, and therefore its energy, and therefore its mass. So to speed it up a little more takes even MORE energy, which increases its speed, and therefore its energy and therefore its mass...

So, doing the math, it turns out that it takes an infinite amount of energy to speed something up to light speed.