Why you can't go the speed of light ( for some people who asked)

[dream431ca]

Actually it is VERY VERY hard to reach those speeds.. here's an example: Lets say you have a train going 20km/h and you have someone inside the train run in the direction of travel at 20km/h.

So how fast would the guy be going relative to you standing outside watching him?? 40km/h right??

Well...now lets say the train is going 200,000km/s and the guy is running down the train in the direction of travel at also 200,000km/s. If you could see this happen..you would expect to see the guy run at 400,000km/s right?? WRONG! He would actually be running at 221,000km/s. Here's why:

When something goes that fast...basically the energy is not propelling the vessel anymore, it's giving the object more mass and not acceleration. So there is a point where energy is converted to mass and it becomes alot more hard to accelerate the object because at the same time energy is building more mass on the object, so you get to a point where mass and energy cancel and the object will not accelerate anymore. If you try and go faster..you will just build up more mass and the object will slow down. In theory..to go the speed of light the object will have the mass of the entire universe before it even gets to the speed of light.

Hope this helps

 

[CyberSh33p]

sweet.... I wanna be a dense slow running death-man! I'd pwn everything near me

 

[Letters]

Demo, please!

 

[Foxtrot]

So the faster you go the more mass you gain? I don't get it...

 

[Reaktor4]

Me either. I dont see how mass can be created from travelling a certain speed. I mean do you just magically get fatter or what?

 

[dream431ca]

Hey guys it's a THEORY ok?? it's hard to picture but THEORTICALLY that what happens.

 

[Foxtrot]

Hey guys it's a THEORY ok?? it's hard to picture but THEORTICALLY that what happens.

Can you explain why?

 

[Vigilante]

200,000 Km S??S??? god damn that's fast.

I betch if I strapped a bunch of the Saturn V rockets to my bum bum I could go pretty damn fast. :E

Seriously though, I really dont understand why you wouldnt be going 400,000. If you were traveling at 200,000 and then started running foward at 200,000 how can you NOT be going 400,000? I'll ask my physics teacher this tomorrow.

 

[dream431ca]

200,000 Km S??S??? god damn that's fast.

I betch if I strapped a bunch of the Saturn V rockets to my bum bum I could go pretty damn fast. :E

Seriously though, I really dont understand why you wouldnt be going 400,000. If you were traveling at 200,000 and then started running foward at 200,000 how can you NOT be going 400,000? I'll ask my physics teacher this tomorrow.

LOL!!


Things act differently when you go that fast.

 

[Foxtrot]

That would work at any speed though wouldn't it? As long as your speed doesn't exceed the speed of the object you are in you will always being going as fast as it.

 

[dream431ca]

That would work at any speed though wouldn't it? As long as your speed doesn't exceed the speed of the object you are in you will always being going as fast as it.

What I am trying to say is if an object is going a certain speed and you are inside the object running the exact same speed in the direction of travel....At higher speeds..this would get very weird. It's one of einstein's special theory of relativitys.

 

[johnnypoopoopant]

if you go the speed of light in like a jet wont the jet blow up or something b/c its too fast

 

[hasan]

but 200,000 is not that much .. I mean, it's not close to the speed of light. only one 10th of it.

 

[dream431ca]

if you go the speed of light in like a jet wont the jet blow up or something b/c its too fast

In air....the jet would disntigrate. In a vacuume though..it would not.

 

[Jakeic]

isn't it 3.2 x 10^8 m/s or something?

 

[Reaktor4]

mps not mph

 

[Lil' Timmy]

it's just special relativity guys. let's take kinetic energy as a starting point. you've probably learned that kinetic energy (kE) equals 1/2 mass*(velocity^2). that's actually wrong, or more aptly, it's just an approximation. the relativistic equation isn't kE=1/2m*v^2, it's kE=m*c^2*(1/sqrt(1-v2/c2) - 1), which is ~m*v^2 for v <<< c.

so kinetic energy is actually much higher for objects at relativistic speeds than one would expect using classical models. by looking at the equation above, you can see that, in fact, as v --> c, kE --> ∞. so it'd require an infinite amount of energy to accelerate an object with any mass to c.

relativity includes a mass-energy equivalency relationship. because of this, any time force is used to accelerate an object, it's apparent velocity increases (obviously) but so does it's apparent mass. like the kinetic energy, this effect is asymptotic with respect to v(c). at the tiny speeds we're used to the mass change is not observable. but it has been observed at relativistic speeds, in particle accelerators (like fermilab, cern, etc.).

the relative speeds problem is also similarly resolved. let me rephrase it for clarity:

car A is traveling in a straight line at 80mph. car B is traveling in the opposite direction on the same street at 70mph. therefor their speed relative to one another is 80+70 = 150 mph.

now, car C is traveling in a straight line at 0.8c (80% the absolute speed of light). car D is traveling in the opposite direction on the same street at 0.7c. so isn't their relative speed 80%c + 70%c = 150% c??

the answer is no, and here's why: the speed of C relative to D is not 0.8c + 0.7c, it's (0.8c+0.7c)/(1+0.8c*0.7c/c^2) according to v = (v1+v2)/(1+v1*v2/c^2). as you can see at tiny Cs and Ds (like we are used to) relative speed is essentially C+D. but as C and D --> c, v --> c. it's not as complex as it looks, just plug in some numbers and check it.

now if you want to know how those equations were derived, well, i can't tell you. i'm not a physicist, so i've never read the original relativity papers, just other author's simplifications.

 

[Phisionary]

Well, Lil' Timmy covered a bit, but I'd already wrote this. I start a bit more basic. Tell me if it makes no sense.

Seriously though, I really dont understand why you wouldnt be going 400,000. If you were traveling at 200,000 and then started running foward at 200,000 how can you NOT be going 400,000? I'll ask my physics teacher this tomorrow.

It's rather complicated to explain.

This all deals with Einsteins theory of relativity. I get them confused sometimes, but this should be what is called his Special Theory of Relativity. It's special I think because it describes relatively specific phenomena involving very high velocities?? I dunno.

Anyway, Einstein had a theory that nothing could travel faster than the speed of light. Following from this idea, he tried to figure out what would have to be true about the laws of physics to make this happen.

Let's consider a theoretical situation that ties into what dream431ca proposed... Two objects are moving toward one another. Let's say, two people, each walking 4kph. They run into one another. It's pretty obvious to anyone who's gotten through grade school that they hit each other with a combined velocity of 8 kph. Ouch.

Let us assume that we have two spaceships. Each are travelling through deep space, at about 90% of the speed of light (light travels at 300,000 kilometers per second. A brisk pace to say the least. Note: this is the speed of light ina a vacuum as light travels slower through glass, air, water, etc.). They are headed directly towards one another. If they collided, this same assumption would lead you to believe that they had just crashed into each other at 180% the speed of light, or about 540,000 kilometers per second.

But, to the pilots of one of those ships, it would appear that the other ship was moving faster than the light.

I think I will have to sidetrack for a moment.

Let's pretend something else for a second. There are, again, two spaceships. One is sitting on the surface of the earth, the other is in deep space, flying out into the cosmos. Neither spaceship has windows, they are completely selaed and self-contained, and have no method of communicating outside the ship.

The ship that is flying in space is accelerating, at a rate of exactly 1 G (a Gee is a unit of measurement equal to the pull of earths gravity at sea level). This ship's drive is very advanced, and works silently, without vibration or other effects noticable within the ship.

Presume for a moment that the astronauts aboard each of the ships, one resting on teh earth, one accelerating through space, have no idea if they are on earth or in space (maybe some NASA joker slipped 'em a mickey the day before launch and they cant remember ). Each decides to perform some experiments. They bounch a rubber ball, use a computer, grow soem yeast in a cell culture. One well developed idea (I think :E) by Einsteins time was that the experiments on the ship and the experiments on the ground would have exactly the same results, were the environments sealed well enough that the outside world was not affecting them. The only outside force is the force of acceleration in one ship, and the effects of gravity on the other.

What this theory demonstrates is that no matter how fast you are moving, the laws of physics apply in the same way...
(It also demonstrates a theory that gravity and acceleration are essentially the same thing, but that's for another time)

So, back to our first two ships, on a collision course.

In the moment of impact, it would seem that two objects were colliding at a speed faster then the speed of light. Since einstein thought this was impossible, something had to happen to prevent that from happening.

The only answer that really fit was that an object travelling at so-called relativistic velocities, would not experiance time at the same rate as an object at rest (not moving at all).
Note: In truth, all objects are affected by this, but the amount of this effect is indetectably small until you start moving at many thousands of miles per hour. Relativistic speeds are conventionally considered to be significant fractions of the speed of light, say 30,000 km/sec. or something like that.
Another note: These time dialation effects have been proven to a reasonable degree. Ask me how if you wish...

What does this mean to our doomed crashing spaceships? Well, as objects begin to move at very high speeds, the local effects of time would start to divirge, so that a light source in front of them would always appear to be arriving at exactly the same velocity, or, exactly the speed of light. They would be able to detect change in the light in the form of blue shift, but that is another story.

So our spaceships, to an external stationary observer, are each travelling at 90% the speed of light. But inside the ship, time has slowed for those inside so that, if the two should collide, it would appear that the sum of their velocities was still less than light-speed.

Whew... I have to take a break. If anyone wants to know why the mass or these ships sould also increase, I can try my best to explain. If something is unclear I can try to clarify as well.

I'm no professional physicist, mind you, just an interested party.
Please! Comment if you like. I'm betting no-one actually read all this, it would be fun if I was wrong though :cheese:

 

[hasan]

I read it all on some parts I didn't get your point. like, ok, what's that experiment thing inside the ship?

I'd rather you give me a source (aka link) that talks aobut mass increase as you approach C, I always thought mass starts to turn into energy as you approach C.

 

[Phisionary]

sorry. I lost a lot of my links to physics sites. I might be abel to find em again...

The experiment in the ship is an example of how and why the laws of physics need to be the same regardless of velocity. Physical law is relative to your motion, not the motion of some theoretical 'zero velocity'. Maybe that makes some sense? I don't know exactly how to put it...

Mass doesn't turn into energy exactly (though they are kinda the same thing). The energy of acceleration is turned into mass...

Well, search a link on that if you really want to know, there's quite a few good sites I've seen...

if I get time I'll try and elaborate on what I do know of the mass/energy connection. I'd have to think it over, it's not exactly useful everyday knowledge. I do this for me mostly I bet some sites explain better than I do.

 

[CyberSh33p]

probably said already, but gaining mass != gaining volume.

 

[moppe]

Then we'll just have to get a faster light.

 

[Phisionary]

probably said already, but gaining mass != gaining volume.

yes. actually, the faster you go, the thinner you get.

 

[KiNG]

keep going phisionary. im reading.

tell me about how gravity and acceleration relate and how time dialation has been proven. what are blue shifts and why does mass expand im lost on why.

 

[TIIMMYY]

If you were going at the speed of light, and there was a light behind you, wouldnt everything be black behind you because the light cant reach you?

 

[Phisionary]

ok. thx for the interest
First. time dilation, or compression, or whatever. (I'm not exactly sure what to call it)

Well, there are things that exist known as cosmic rays. They are particles (I don't remember what exact type) that are travelling very very fast. Some are emitted from the sun, some from stars, and some are the remenants of the radiation released from the big bang I believe. A form of background radiation.

Sometimes these particles hit the earth's atmosphere, and this causes the particle to decompose into several other particles of different, lower-energy types. Scientists knew the half-life :E of thes particles, in other words, these particles were unstable when they were created, and after a certain period of time that particle will radiate some energy and become a different, possibly stable, particle.

Now, let's assume that time dilation does not occur. A cosmic ray, travelling at incredible speeds, crashes into the atmosphere. It breaks into a number of other particles, which are unstable. These particles decay into stable forms after a period of time, say... 1/1000 of a second (I have no idea of the accuracy of these numbers; it's just an example). Now, if these particles took 2/1000 of a second to reach the ground-based -etectors that scientists used, then they would hardly ever detect the unstable-type particles at ground level.

However, cosmic rays travel at extremely fast speeds, sometimes close to the speed of light (IIRC). And, scientists found that they did not detect only the stable forms of particles, but found the unstable ones as well, that should have turned into the more stable form by the time they reached the detectors...

So, this is one form of evidence that these particles, travelling at 'relativistic' speeds, are actually moving through time slower than a similar particle that was not moving; those which had been studied on earth to determine the decay rate (half-life).

Another test is simply to have two very accurate clocks (i.e. an atomic clock). Set them to the same time. Place one at a stationary location. Put the other in a fast plane and fly at high speeds for a long time. The one from the plane will be slower by millionths or maybe thousandths of a second. This has been demonstrated scientifically several times.

Okay. Two, blue-shift.

Remember, I said that light will always appear to move at the exact same speed no matter what velocity an observer travels at. A light measuring machine will measure light at 300,000 km/sec. on earth and 300,000 km/sec. in a spaceship travelling at 90% the speed of light.

Indeed, if you have a flashlight on board the ship, it would look and work the same as the one on earth. no difference would be noticed.

No imagine that your high-speed ship is headed towards a star. This same star is visible from earth, and earth and the star are not moving relative to one another.

On the ship, looking through a forward facing window, the star would appear to be more blue.

This is due to the change in velocity's effect on the wavelenght of the light. Wavelength is independant of speed. Wavelength is a term for the frequency of light (as light is a wave, in a manner similar to sound waves); it's color. The electro-magnetic spectrum is a term describing the many forms a photon (a light-particle) can take when at different frequencies. On this spectrum are radio waves (used for, well, duh), microwaves (yes, the cooking kind), infrared (night vision), visible light (what we see with our eyes), ultraviolet (sunburns), x-rays, and gamma rays (a dangerous by-product of nuclear reactions, among other things). All that seperates these are the frequency of the wave.

Igf you've ever been to a NASCAR race, or seen one on TV, you'll know that distinctive sound right at the moment the cars pass by. As they approach, a high pitch whine, a moment after, a deeper tone. Well, anyone past high-school physics should know this as the doppler effect. It is the sound waves being compressed by the cars motion as the car nears us (the stationary listener), and strecthing out as the car passes. Of course, sounds the observer might make (maybe a bullhorn) would sound similarly to the driver of the car, should he be able to hear anything but his engine....

This principle also applies to light waves. Back to the high speed spaceship. As it approaches the star, the frequency of the light is compressed. A normally white-ish star would attain a blue-ish hue, since blue is the color towards the top (higher frequency) part of the visible spectrum.

Well, I think I got that all right. I think the rest'll have to wait till tomorrow.

Edit: I'm thinking some of my explanations may not have been 100% accurate. I'm not sure. If anyone can see a problem, please point it out :thumbs:

 

[Phisionary]

If you were going at the speed of light, and there was a light behind you, wouldnt everything be black behind you because the light cant reach you?

Yes, but since (according to all the physics we know presently) this isn't possible, it'll never happen.

 

[Jakeic]

considering how big the galaxy is, then how big the universe is, and we have never left the orbit of our own planet, i think it is safe to assume we don't know a whole lot yet.

 

[lePobz]

Travelling the speed of light is most likely a far off target, but hopefully it isn't needed ... bending space to make something move faster than light whilst relative to space (because space is being shrank infront of and expanded behind the vehicle) is not travelling fast at all.

It's called Warp, people... and it's theoretically possible.

 

[falconwind]

Travelling the speed of light is most likely a far off target, but hopefully it isn't needed ... bending space to make something move faster than light whilst relative to space (because space is being shrank infront of and expanded behind the vehicle) is not travelling fast at all.

It's called Warp, people... and it's theoretically possible.

Indeed, travelling faster than the speed of light is simply impossible. It is, however, possible to "cheat". Warping space is one such way to circumvent special relativity.

You could, I believe, achieve the speed of light, however. You'd simply have to have zero rest mass.

Then again, the speed of light isn't very fast, astronomically speaking. It would only take 500 seconds to reach our sun, but it would take 4.3 years to reach the closest star, Promixa Centauri.

 

[Sprafa]

Light speed hasn't always been the same.

 

[burnzie]

My Head A splode!

 

[dream431ca]

Psisionary, you are very good. :thumbs:

 

[Maxi]

Sprafa! I DEMAND PROOOOOOOF!

Anyway, a very cool post, and since i'm taking physics... I understand some of it

 

[hasan]

as for the relationship between gravity and acceleration, well, gravity IS acceleration, but AFAIK, acceleration doesn't have to be gravity.

don't take my words for granted, but gravity occurs because objects wrap space, or "bend" it, like a ball would do to a net you know..
for some reason, this bending this bending causes objects to 'fall' and move towards the object.
but we don't feel the bend of space, for us, it's still straight.

imagine a one dimensional world, let it be a thread/string, and there is something moving inside this string. if you come and form this string into a circle, the object inside the string will still see the world as a straight line.

 

[Parrot of doom]

My understanding is that the closer to the speed of light you get (186 000 mps), the more energy you need to accelerate. To accelerate to the speed of light, you need an infinite amount of energy, which of course is not possible.

As for gravity, imagine space as a mattress. Put a football on the mattress, and it will sink down slightly (a small moon). Put a solid steel football on the same mattress, and it will sink down more (a large gas giant). The angle of the curve is a good analogy for the strength of the gravitational field.

The real headbanger comes when you think of a black hole, which some people say sinks down through the mattress to an infinite depth.

 

[PvtRyan]

Every object has a rest mass, the mass when it's not in motion. When you're in motion, your mass increases (you get stretched too, when you walk you're longer than when you stand still) and approaching c, this mass becomes infinite, requiring an infinite amount of energy to make you go faster, which doesn't exist obviously. The particles that do travel at c (photons) have no mass.

Also a funny thing about light is that, when someone is chasing a lightbeam at say 100,000 km/s, the lightbeam still moves away from him at 300,000 km/s, in contrast with your natural reaction of 200,000 km/s. So light is not relative.

Another thing is that for a moving particle, time passes slower than for a static observer, astronauts gain a few mili seconds in space, and technically, someone in a rocking chair will have time passing slower than someone in a regular chair. At c, the time stands still, from the perspective of a lightbeam you travel instantly. This is another thing that makes travelling at c impossible: you arrive instantly, you only have 0 seconds to steer, none. You are literally everywhere and nowhere in the universe.

 

[burnzie]

Every object has a rest mass, the mass when it's not in motion. When you're in motion, your mass increases (you get stretched too, when you walk you're longer than when you stand still) and approaching c, this mass becomes infinite, requiring an infinite amount of energy to make you go faster, which doesn't exist obviously. The particles that do travel at c (photons) have no mass.

Also a funny thing about light is that, when someone is chasing a lightbeam at say 100,000 km/s, the lightbeam still moves away from him at 300,000 km/s, in contrast with your natural reaction of 200,000 km/s. So light is not relative.

Another thing is that for a moving particle, time passes slower than for a static observer, astronauts gain a few mili seconds in space, and technically, someone in a rocking chair will have time passing slower than someone in a regular chair. At c, the time stands still, from the perspective of a lightbeam you travel instantly. This is another thing that makes travelling at c impossible: you arrive instantly, you only have 0 seconds to steer, none. You are literally everywhere and nowhere in the universe.

:|

wow...

 

[Phisionary]

Every object has a rest mass, the mass when it's not in motion. When you're in motion, your mass increases (you get stretched too, when you walk you're longer than when you stand still) and approaching c, this mass becomes infinite, requiring an infinite amount of energy to make you go faster, which doesn't exist obviously. The particles that do travel at c (photons) have no mass.

I think you have it backwards. I'm pretty sure that you get thinner (i.e. compressed in a longitudinal direction) with increasing velocity.

I'd try to form an explanation but my mental image of this idea is skecthy, I'd probably confuse everyone if I tried...

 

[Alec_85]

If all this is true, how come everything works perfectly in Star Trek (w8 I'm serious)? AFAIK, their warp drive is actually based on "working" theories that "would" work if we simply had the technology to back it up. At least that's what I've from their offical forums etc. Same goes for all their little experiments they have in their episodes.

Same goes for physicians who says that it's IMPOSSIBLE to go beyond light speed. Since the difference between Star Trek Warp 1 (pure light speed) & Warp 2 is NOT light speed times 2 (more like ^10 or something). I wonder how they reason when it is said that ST is based (based on is such a loose expression) on current theories on space travel? They should really say, that it's impossible with our current level of development but noooo

I wonder why ST Warp is not the same as SW Warp? Strange. Either their galaxy is 1/10 of ours or their Warp is based on some other theory.

Yeah I know. I'm a sci-fi freak :E

Edit:

I think you have it backwards. I'm pretty sure that you get thinner (i.e. compressed in a longitudinal direction) with increasing velocity.

Hmm maybe that explains why SW & ST ships gets stretched when they go to Warp speed. Have no idea what direction longitude references to though.