# Going the Speed of Light



## OneKube (Aug 2, 2009)

If you're traveling at the speed of light you see that time is stopped.. like if you go 40 light years and look back you see the past. Anyway if you doing the speed of light you see time stopped but really it is still going, because it is taking time for you traveling the speed of light. Sorry I was discussing this with someone.


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## V-te (Aug 2, 2009)

(This is how I understand)

If someone on earth were watching a spacecraft travel at the speed of light, the travelers time would appear to be passing slower, than them.

However, from the travelers point of view, the time is passing the same for them. (It's kinda hard to explain it)

But I do know this, We could never travel at the speed of light. maybe close to it like 99.99999999% but never truly 100%. Just like absolute zero.


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## imaghost (Aug 2, 2009)

Now I thought a while ago about this kind of thing, that if I toss a ball in the air away from me, and you go the speed of light to go catch it, you would miss it because you are going slow relative to me. it would take you years to get there. but a little later i thought, you would only have to go the speed of light for like a nano second, so you would catch it.


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## RainbowBoy (Aug 2, 2009)

OneKube said:


> Sorry I was disguising this with someone.


You mean Discussing it with some one else

I think its just like cubing (I hope you don't mind me mentioning cubes in this thread) Where you do a cube really fast and you think time is still going but when you look at it it has only past a few seconds or minutes.


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## Zeroknight (Aug 4, 2009)

This raises another question of mine:

When moving faster than the speed of sound, can you hear anything? I doubt it, but I've never done it, so I have no idea.


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## brunson (Aug 4, 2009)

Yes. Otherwise fighter pilots couldn't use their radios at supersonic speeds. With all these questions, whether speed of light or speed of sound, it's the locality of reference. The air in the cockpit is not moving in relation to the pilot, therefore sound propagates normally within the local frame of reference. The earth is moving thousands of miles per second, but within it's local frame of reference, sound propagates normally.


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## xXdaveXsuperstarXx (Aug 4, 2009)

I hate this thing where people think going the speed of light affects time. Here's what happens when you go the speed of light. 

1. You would have no shadow because light doesn't get to you.

2. It would be very, if not pitch black where you are running because light can't reach you.

3. You will hear nothing because you are going much faster then the sound barrier. (however though it would probably burst a humans eardrums)

4. Even if you did manage to "spin earth the other way" you wouldn't effect time itself, oh yeah, you would also probably cause a few major earth quakes to because of the earth shifting, but you would never be able to shift the earth because the wind force necessary would be extremely immense and would never be achievable by any living thing. If you go the speed of light to catch a ball you would get the in a matter of milli.(much much smaller though)seconds. It would not take forever. If a space craft was going the speed of light you would not see them because the human eye can only take a certain amount of pictures per second. Even a high-speed camera couldn't even pick it up. Now if this craft was 1 billion miles long and a little farther then the sun and high speed camer might be able to pick it up.


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## 4Chan (Aug 4, 2009)

xXdaveXsuperstarXx said:


> I hate this thing where people think going the speed of light affects time. Here's what happens when you go the speed of light.
> 
> 1. You would have no shadow because light doesn't get to you.
> 
> ...



:fp You dont understand relativity. Lrn2physics.

Its called time dilation, time is slowed when you travel at very high speeds, or in the presence of immense gravity.


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## xXdaveXsuperstarXx (Aug 4, 2009)

> time is slowed when you travel at very high speeds, or in the presence of immense gravity.



So if what you say is true, why can't we see rays of light in the air on earth?

Then the rays must still be going too fast for us to see? So it is still going very fast.


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## 4Chan (Aug 4, 2009)

xXdaveXsuperstarXx said:


> > time is slowed when you travel at very high speeds, or in the presence of immense gravity.
> 
> 
> 
> So if what you say is true, why can't we see rays of light in the air on earth?



Instead of trying to save face and making fallacies, you should take a physics class or perhaps use a wiki. 

http://en.wikipedia.org/wiki/Theory_of_relativity#Special_relativity


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## xXdaveXsuperstarXx (Aug 4, 2009)

Wait, what are we trying to prove? I got kind of lost on that.

EDIT:

Okay, so you would go slower because of relatively or whatever you call it. But if you were going the speed of light you would simply slow down. But I do not believe that you would change time, for you are not going at the same speed as the speed of light because it would slow you down. Either if I'm right or wrong. I firmly believe that it is impossible to change time or slow down time. I believe that time happens as it is. It is not something that we can control.


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## 4Chan (Aug 4, 2009)

xXdaveXsuperstarXx said:


> *I hate this thing where people think going the speed of light affects time. Here's what happens when you go the speed of light. *
> 
> 1. You would have no shadow because light doesn't get to you.
> 
> ...




Im disproving your fallacy.


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## xXdaveXsuperstarXx (Aug 4, 2009)

Well, I don't believe it changes time because I'm using logic . If you were in a craft going the speed of light you would experience time like other people, you are just experiencing it at a different speed then most. However if it were real the G-Force would probably rip you skin off. So, this would never happen.


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## Tim Reynolds (Aug 4, 2009)

Stop guessing about what life would be like if you were going the speed of light.

It's not possible. That's a basic fact of relativity.


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## xXdaveXsuperstarXx (Aug 4, 2009)

We know it's not possible we're just doing a hypothetical conversation. Now if this were based in space it would be physically possible because there's no gravity.


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## 4Chan (Aug 4, 2009)

Ughhh, your logic is flawed, because you're not basing your assumptions on FACTS. (i.e. Einsteins relativity.)

1. Only light can travel at the speed of light because of its mass (or lack thereof).

2. Stop trying to avoid the proven fact that time is dilated in the presence of gravity and speed.


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## mr.onehanded (Aug 4, 2009)

xXdaveXsuperstarXx said:


> We know it's not possible we're just doing a hypothetical conversation. Now if this were based in space it would be physically possible because there's no gravity.



:fp
It wouldn't seem that moving faster would slow down time, but it does. There isn't really a reason behind it's just the way it is. Basically, If two objects are moving towards each other you can use the equation velocity1 + velocity 2 to find how fast they are moving to each other. As things turn out, this equation is near accurate at low speeds but when you use speeds extremely fast - the speed of light - time slows down exponentially. This can be proven by a simple experiment, if there was a source of light on one end of a table and something to measure the lights speed on the other end, if you were to measure the speed of the light you would find the speed of light, of course, but if you were to put the light source on wheels and pushed it towards the thing measuring the speed of the light, you would still get the speed of light. This is because the speed of light can not be exceeded. So if two photons of light were moving towards each other they would be moving at each other at not twice the speed of light, but the speed of light. This was one of Einstein's largest breakthroughs because he changed everything the we hold to be true, and thus redefined all of physics.

I have no formal education on this topic, but all of the knowledge from this post was taken from this college lecture. If you are interested in understanding relativity more thoroughly check it out. 
http://www.youtube.com/watch?v=nNgzqpKZwhE


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## xXdaveXsuperstarXx (Aug 4, 2009)

Okay, so if it goes slower, it goes slower or is it that it goes slower but it doesn't. Or is it just that we have a flawed way of measuring time? I really don't get it.


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## Ellis (Aug 4, 2009)

xXdaveXsuperstarXx said:


> Well, *I don't believe it changes time* because I'm using logic . If you were in a craft going the speed of light *you would experience time like other people, you are just experiencing it at a different speed then most.*



What exactly are you trying to argue?


If you could travel on a light wave from the sun to the earth, how long would it take you?


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## xXdaveXsuperstarXx (Aug 4, 2009)

> If you could travel on a light wave from the sun to the earth, how long would it take you?



8 minutes (maybe 7, I don't remember). So your trying to say that the light itself takes 8 minutes. But if your on the light it's much slower?


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## Ellis (Aug 4, 2009)

xXdaveXsuperstarXx said:


> > If you could travel on a light wave from the sun to the earth, how long would it take you?
> 
> 
> 
> 8 minutes (maybe 7, I don't remember). So your trying to say that the light itself takes 8 minutes. But if your on the light it's much slower?



We've already verified SR, is that your final answer?


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## xXdaveXsuperstarXx (Aug 4, 2009)

> We've already verified SR, is that your final answer?


Um, yes? Why?


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## Ellis (Aug 4, 2009)

xXdaveXsuperstarXx said:


> > We've already verified SR, is that your final answer?
> 
> 
> Um, yes? Why?



Because it's wrong, in more ways than one. I wanted to give you a second chance. Sorry, I'm not here to argue or debate 100+ years of physics research, so I won't go much further. I was trying to propose an easy question that would help you think about it. The answer was no time, not ~8 minutes or "much slower" than 8 minutes. You should take a physics class in the future, it's fun stuff.


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## shelley (Aug 4, 2009)

I've been a TA for a relativity/quantum class for the past few weeks. xXdaveXsuperstarXx, just shut up and do some research before you embarrass yourself further.

It's true that none of us can travel at the speed of light. However, here's a real life example that illustrates time dilation: Muons are electron-like particles emitted from cosmic rays. They travel at relativistic speeds and have a short half life, such that without relativistic effects they would decay less than a kilometer after entering the earth's atmosphere. However, they do manage to reach the earth's surface due to time dilation (because they are traveling so fast, time passes at a different rate for the muon compared to observers on earth).

When you deal with relativity (very fast things) and quantum mechanics (very small things), there are many counterintuitive results. Relativistic time dilation has been mentioned, there is also relativistic length contraction, which makes things even weirder. But I'll let you find out about that one yourself (look up the pole-barn paradox). You can't just say "this is impossible, based on the experience of things I've observed," because nothing in our realm of experience can prepare us for the physical behavior of things that are that small or moving that fast. It seems illogical, but only because our logic is based on our experience of macroscopic, slow moving things.


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## arud45 (Aug 4, 2009)

Time is relative to your position, it's different based on speed. Someone else going the speed of light has no affect on you, and it would seemingly have no affect on them. But when you compare the two, they differ.

anyway, with today's technology/theories it is impossible to speed something up to the speed of light because it would take an infinite amount of energy.


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## brunson (Aug 4, 2009)

GPS works because every satellite carries a highly accurate atomic clock and these clocks allow the satellites to know where they are in relation to each other with great accuracy. However, because the satellites are travelling at such a high speed relative to the earth calculations must take into account relativistic time dilation in order to remain accurate.

Short form: The clocks on the satellites run slower than if they were on the ground. It's a fact, it's been measured, Einstein was right. Just because it isn't "logical" to you doesn't make a difference.


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## peterbat (Aug 4, 2009)

shelley said:


> When you deal with relativity (very fast things) *and quantum mechanics* (very small things), there are many counterintuitive results.


Oooo, please elaborate.  QFT FTW!






EDIT: I think this thread is ready to turn into the "Loop Quantum Gravity" thread, don't you?


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## daniel0731ex (Aug 4, 2009)

if you travel at the speed of light and met another person traveling at the speed of light 
in an opposite direction, the relative speed would still be the speed of light


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## JBCM627 (Aug 4, 2009)

Thank you Shelley...

The best analogy I've heard to describe special relativity:


> Consider two people sitting across the table from each other. A block is set on the end of the table. Person A observes that the box is to the right, and person B observes that the box object is to the left. But how can the box object be both to the right _and_ left?


Special relativity "paradoxes" are no more complex than this - two people observing the same thing from a different point of view. Note that I put paradox in quotes... they aren't actually paradoxes.

More technically, both people at the table see the projection of the box into a flat, invariant, 2d (or 1d if you constrain it) euclidean space. Relativity is the analog of this - but instead deals with an invariant hyperbolic (non-euclidean) spacetime. We only see the projection of objects in this 4d spacetime onto our euclidean space, which is why we see apparent "paradoxes".


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## Kyle™ (Aug 4, 2009)

Actually lots of stuff can travel the speed of light. this reply is to cubes=life.
light being massless doesn't have much to do with it. galaxies weigh more than you can imagine and they are traveling apart at the speed of light.


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## FredM (Aug 4, 2009)

Ok. I had also the problem when imagining what happens with Relativity.

Imagine you want to get to a star 4 light years away. For the traveller in the shuttle, it can take hime less than four years if he travels at a sufficient speed ?


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## brunson (Aug 4, 2009)

KYLE ALLAIRE DROPS BOMBS! said:


> Actually lots of stuff can travel the speed of light. this reply is to cubes=life.
> light being massless doesn't have much to do with it. galaxies weigh more than you can imagine and they are traveling apart at the speed of light.


No they aren't, that would violate special relativity. 

If you fire two projectiles in opposite directions at non relativistic speeds, you can compute their relative velocity by summing their speeds relative to you, e.g. 700fps + 700fps = 1400fps. 

That doesn't work for relativistic speeds. If each object is travelling away from you at 3/4 the speed of light, they are *not* travelling apart from each other at 1.5 times the speed of light, that's impossible.


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## Kian (Aug 4, 2009)

KYLE ALLAIRE DROPS BOMBS! said:


> Actually lots of stuff can travel the speed of light. this reply is to cubes=life.
> light being massless doesn't have much to do with it. galaxies weigh more than you can imagine and they are traveling apart at the speed of light.



False. 

A basic rule of the universe is that anything without mass is traveling the speed of light, anything with mass is traveling at something less than that. Galaxies are not traveling at the speed of light.

Edit: Brunson explained the galaxy issue more thoroughly, I didn't see it when I posted.


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## Ellis (Aug 4, 2009)

FredM said:


> Imagine you want to get to a star 4 light years away. For the traveller in the shuttle, it can take hime less than four years if he travels at a sufficient speed ?



No. If a star is 4 light years away, there's no way anything is getting there in faster than 4 years (or in 4 years unless it is light itself).


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## Kyle™ (Aug 4, 2009)

Completely False kian.


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## brunson (Aug 4, 2009)

Ellis said:


> FredM said:
> 
> 
> > Imagine you want to get to a star 4 light years away. For the traveller in the shuttle, it can take hime less than four years if he travels at a sufficient speed ?
> ...


From an external observer's point of view. The ship were to travel at near light speeds the passage of time to the occupants would slow so it would seem less than 4 years.


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## 4Chan (Aug 4, 2009)

KYLE ALLAIRE DROPS BOMBS! said:


> Actually lots of stuff can travel the speed of light. this reply is to cubes=life.
> light being massless doesn't have much to do with it. galaxies weigh more than you can imagine and they are traveling apart at the speed of light.



I assume this is what you mean by "traveling apart"

As quoted from wikipedia:

Universal expansion

The expansion of the universe causes distant galaxies to recede from us faster than the speed of light, if comoving distance and cosmological time are used to calculate the speeds of these galaxies.

In these examples, certain influences may appear to travel faster than light, but they do not convey energy or information faster than light, so they do not violate special relativity.



What i learned about mass was that, due to "length contraction", nothing past a certain mass can exist past the speed of light.

Also quoted from wikipedia:

An observer at rest viewing an object travelling at the speed of light would observe the length of the object in the direction of motion as zero. Among other reasons, this suggests that objects with mass cannot travel at the speed of light.

Im not sure what youve learned, but thats what i learned.

Also, i am also aware of relativistic particles such as neutrinos and cosmic rays traveling near the speed of light. as shelley stated.


EDIT: by the time i finished my reply, others had already replyed. (x


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## brunson (Aug 4, 2009)

KYLE ALLAIRE DROPS BOMBS! said:


> Completely False kian.


No, completely true.

http://math.ucr.edu/home/baez/physics/Relativity/SR/velocity.html


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## Ellis (Aug 4, 2009)

brunson said:


> Ellis said:
> 
> 
> > FredM said:
> ...



Well yea, oops. Even after the question I posed earlier 

I don't know why I was thinking external reference.


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## shelley (Aug 4, 2009)

Ellis said:


> brunson said:
> 
> 
> > Ellis said:
> ...



To be fair, he didn't specify a frame of reference.


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## JBCM627 (Aug 4, 2009)

brunson said:


> KYLE ALLAIRE DROPS BOMBS! said:
> 
> 
> > Completely False kian.
> ...


This doesn't hold if space itself is expanding (which is thought to be the case with our universe). This might be what KYLE is talking about, but this is something completely different than traveling faster than light in a universe that isn't expanding, and thus isn't considered in special relativity. It also probably isn't something people should think about if they don't understand special relativity first. Most accurately put, objects with mass can't accelerate to the speed of light.


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## Ellis (Aug 4, 2009)

shelley said:


> To be fair, he didn't specify a frame of reference.


True, but I should have specified.


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## brunson (Aug 4, 2009)

JBCM627 said:


> brunson said:
> 
> 
> > KYLE ALLAIRE DROPS BOMBS! said:
> ...


I was avoiding the issue of expansion, trying not to muddy the waters.


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## JBCM627 (Aug 4, 2009)

brunson said:


> I was avoiding the issue of expansion, trying not to muddy the waters.


Probably a good plan.

Edit
(Btw, that wasn't intended as a slap to you, but to people like xdaveXxthing)


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## Kyle™ (Aug 4, 2009)

We'll see who can run faster than light when I get my cheetah leg implants. WATER'S GETTIN' MUDDY.


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## nitrocan (Aug 4, 2009)

Oh, this is why my timer kept showing 0.02. I'll go slower from now on.


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## miniGOINGS (Aug 4, 2009)

Zeroknight said:


> This raises another question of mine:
> 
> When moving faster than the speed of sound, can you hear anything? I doubt it, but I've never done it, so I have no idea.



The speed of sound depends on the density of air pressure, which effects the speed at which sound travels. If you were going faster than the speed of sound, and sound behind you would not catch you but sound in front of you would hit you faster.

If you listen to an ambulence, the sound gets higher pitched as it's coming towards you, and lower pitched as it's going away from you.

...I think...


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## nitrocan (Aug 4, 2009)

miniGOINGS said:


> Zeroknight said:
> 
> 
> > This raises another question of mine:
> ...



Your first argument was correct but what does the ambulance thing have to do with anything?


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## miniGOINGS (Aug 5, 2009)

nitrocan said:


> Your first argument was correct but what does the ambulance thing have to do with anything?



Thank you . 

Let's say that _you_ were moving, not the ambulance. If you kept moving *directly* away from the ambulence, faster and faster, by the time you got to the speed of sound, you wouldn't hear the ambulance, but you would still be able to hear things that are in front of you or at an angle although the sound would be distorted.

...I think again...


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## nitrocan (Aug 5, 2009)

miniGOINGS said:


> nitrocan said:
> 
> 
> > Your first argument was correct but what does the ambulance thing have to do with anything?
> ...



But that's because the sound is dying, not disappearing.


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## qqwref (Aug 5, 2009)

nitrocan said:


> Oh, this is why my timer kept showing 0.02. I'll go slower from now on.



Yes, you should indeed go slower, always wait at least a second before lifting your hands away from the timer ;-)


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## Carson (Aug 5, 2009)

I have no physics background, or any real knowledge. Here is what I "think" I can take away from this conversation... someone please correct me if I am wrong:

Two objects are moving in opposite directions, each at .75 the speed of light... in reality, the distance between them would be increasing at almost the speed of light, because there speeds would be combined, however due to both objects having mass, their combined speed still cannot reach the speed of light. 

If two photons were moving away from each other, each at .75 the speed of light, then they would really be moving away from each other at exactly the speed of light due to them having no mass.

If two objects are moving away from each other, each at .75 the speed of light, then they would appear to be moving away from each other at 1.5x the speed of light from an observer.

Is this even close, or am I missing the whole point?


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## brunson (Aug 5, 2009)

There are some really good books on introductory relativity, my dad had one that I read when I was about 12, then again when I was 14 and again when I was in college. You seem really receptive to the concepts, so I'll respond.

You can start with only one fundamental: The speed of light (in a given medium) is constant in all frames of reference. No matter what, the speed of light is always constant.



Carson said:


> I have no physics background, or any real knowledge. Here is what I "think" I can take away from this conversation... someone please correct me if I am wrong:
> 
> Two objects are moving in opposite directions, each at .75 the speed of light... in reality, the distance between them would be increasing at almost the speed of light, because there speeds would be combined, however due to both objects having mass, their combined speed still cannot reach the speed of light.


Yes, but not exactly for the reason you describe. 


Carson said:


> If two photons were moving away from each other, each at .75 the speed of light, then they would really be moving away from each other at exactly the speed of light due to them having no mass.


 This is hard to say yes or no to. A photon begins its existence at the speed of light and ends it the same way. Time really has no meaning to photon. It boils down to the time dialation of a particle equals it's mass divided by the the square root of the quantity, speed of light minus its velocity. This is zero divided by sqrt(c minus c) or zero over zero. The c's may be squared, but it doesn't matter, it's still zero over zero.

Essentially, everything breaks down *at* the speed of light, so we can only discuss what happens close to the speed of light.


Carson said:


> If two objects are moving away from each other, each at .75 the speed of light, then they would appear to be moving away from each other at 1.5x the speed of light from an observer.


 No.


Carson said:


> Is this even close, or am I missing the whole point?


I'm sorry, writing this I realized I don't have nearly the time, nor the *skill* to explain this in a reasonable post, but please don't think I ducking the issue. There is a *ton* of stuff on the subject on the 'Net. Google "special relativity paradox" and grab a snack because you'll be in for a really enjoyable next three hours.


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## wing92 (Aug 5, 2009)

i want to take a shot at understanding this. let's say there's a special gun that shoots two rounds opposite directions at .75 times the speed of light. the relative velocities of the two things can only be up to the speed of light. normally they would add up to 1.5 times the speed of light. to fix this problem, given the equation speed=distance/time, and the distance isn't relative (i think) then the time has to change. the speed goes down (i know there's a better way of wording that but you get what i mean) and the time goes up, but the amount of time only goes up for those two bullets. so the two bullets would age faster than the guy that shot the gun. how close am i?


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## imaghost (Aug 5, 2009)

wing92 said:


> i want to take a shot at understanding this. let's say there's a special gun that shoots two rounds opposite directions at .75 times the speed of light. the relative velocities of the two things can only be up to the speed of light. normally they would add up to 1.5 times the speed of light. to fix this problem, given the equation speed=distance/time, and the distance isn't relative (i think) then the time has to change. the speed goes down (i know there's a better way of wording that but you get what i mean) and the time goes up, but the amount of time only goes up for those two bullets. so the two bullets would age faster than the guy that shot the gun. how close am i?


Opposite. The bullets would not age as fast relative to you. The bullet would appear to be going very slow. 


With the speed of light and relativity, I have always wondered if you can make light go faster than, well, light. If you can slow it down, can you speed it up? Black holes, if you don't know, they are basically really massive that even light cannot escape its gravitational field. General Relativity would make it to where the dip goes to a point, and that is why some people think they can send things to other places, transporter thingies. anyway, with that being said, what if I shine a flashlight on black hole? would the gravitational pull make the light go faster? 

I do realize it probably will not, since light is a constant, which is the only answer that I have gotten to this question, by a former Physics teacher, but now why can light go slower since it is a constant?


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## wing92 (Aug 5, 2009)

it's a constant as long as what it's going through is constant. hopefully i got that much right. also, how does the whole relativity thing change when wormholes are added?


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## 4Chan (Aug 5, 2009)

http://www.universetoday.com/2009/06/30/device-makes-radio-waves-travel-faster-than-light/

Faster than light phones? I dont really trust the media completely.
I thought this was impossible when i saw it a few months back.

What do you all think of it?


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## imaghost (Aug 5, 2009)

BS, didn't have to read it, just the title. Radio waves are light. Impossible to go faster than light, since it is light. 


Worm holes and black holes are different.


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## JBCM627 (Aug 5, 2009)

Sure, I can make things travel faster than light too. Just take a laser, point it at one star, then quickly point it to another. The end of the beam moves faster than light.


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## imaghost (Aug 5, 2009)

That is wrong in so many ways... it is not moving in a line across. The photons have a forward motion, not a side motion...


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## Kyle™ (Aug 5, 2009)

pretty sure people have slowed light down. heard about it in a documentary a few months back. shooting light into a cloud of molecules or something. sounded boring so I didn't really research it.


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## Ellis (Aug 5, 2009)

KYLE ALLAIRE DROPS BOMBS! said:


> pretty sure people have slowed light down. heard about it in a documentary a few months back. shooting light into a cloud of molecules or something. sounded boring so I didn't really research it.



.............

Try shining light into...... ummmm ANYTHING

Sorry, I don't want to sound rude... but seriously.


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## ThePizzaGuy92 (Aug 5, 2009)

whenever you look at anything, your looking into the past.


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## Ton (Aug 5, 2009)

OneKube said:


> If you're traveling at the speed of light you see that time is stopped.. like if you go 40 light years and look back you see the past. Anyway if you doing the speed of light you see time stopped but really it is still going, because it is taking time for you traveling the speed of light. Sorry I was discussing this with someone.



My philosophy is that an object in this dimension and remain in current form can not go faster. The only option in theory is travel via other dimensions. e.g. Just has you can fold a paper a 2D object is limited by traveling on the paper but if the 2D object can travel in 3D he can skip space and travel relatively faster than light. Still in the 3D dimension you will not go faster. Any way travel like this you will not be able to go back in time, in my philosophy you could skip and take a shortcut in space.


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## Escher (Aug 5, 2009)

lolfailthread. 
I'm still waiting on qqwref, stefan or dene to post.


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## nitrocan (Aug 5, 2009)

I'm just wondering one thing. If a photon is affected by a gravitational field, then shouldn't it have mass also?


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## brunson (Aug 5, 2009)

http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/photon_mass.html


I believe Einstein explained the effects of gravity as curvature of space, which would account for it's affect on a massless particle.

A friend told me an interesting way of looking at time dilation. 

You may consider your velocity through space and time to be a vector in 4 dimensions with a magnitude of the speed of light. When you're at rest the vector lies along the axis of time, so you are moving through time at the full speed of light. When you begin to move in another dimension, say X, then your vector moves, maintaining the same amplitude, but changing direction. Decomposing the vector into it's component x and t vectors gives you your motion in x and velocity through time.


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## cheiney (Aug 5, 2009)

Is it possible for _any_ form of matter or energy to reach superluminal speed?


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## Ellis (Aug 5, 2009)

KYLE ALLAIRE DROPS BOMBS! said:


> Ellis you sound pretty confused buddy.


Nah. Maybe you just weren't specific enough. "People have slowed down light"?
What do you mean by that? If you shine light into air it slows down, or water, or a plastic bottle. So yea, when you shine it into a cloud a molecules, it's going to slow down... big whoop.


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## Johannes91 (Aug 5, 2009)

brunson said:


> A friend told me an interesting way of looking at time dilation.
> 
> You may consider your velocity through space and time to be a vector in 4 dimensions with a magnitude of the speed of light. When you're at rest the vector lies along the axis of time, so you are moving through time at the full speed of light. When you begin to move in another dimension, say X, then your vector moves, maintaining the same amplitude, but changing direction. Decomposing the vector into it's component x and t vectors gives you your motion in x and velocity through time.


+1 Insightful

I'm a noob at physics and that paragraph cleared up some things very well for me. Much clearer than many really long explanations.


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## brunson (Aug 5, 2009)

cheiney said:


> Is it possible for _any_ form of matter or energy to reach superluminal speed?


There is nothing in SR that prohibits a particle from travelling faster than light (c), only preventing something with mass from travelling *exactly* the speed of light. A particle would have to "skip over" c, making a discontinuous acceleration in order to go from sub light to super light speed, which would violate a ton of physics. 

There is, however, nothing to preclude a particle from being created travelling superliminal. These theoretical particles are called tachyons and subluminal particles are called tardyons.

An interesting property of a tachyon is that the would travel faster the less energy they had. The more energy you put into it, the slower it travels, ultimately requiring an infinite amount of energy to slow down to the speed of light.

All this is theoretical, though...


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## brunson (Aug 5, 2009)

Johannes91 said:


> brunson said:
> 
> 
> > A friend told me an interesting way of looking at time dilation.
> ...


I just asked my friend and he says that with the right units and scaling on the axes, the point-distance formula (distance from (x1,y1) to (x2, y2) = sqrt( (x1-x2)^2 - (y1-y2)^2 ) if I remember right) even results in the correct time and length dilation formulae.


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## Kyle™ (Aug 5, 2009)

If light slows down when it hits everything, please explain how it is getting here from 5 billion light years away through so much space dust and gravitational force. Please. http://www.hno.harvard.edu/gazette/1999/02.18/light.html
edit: directed to ellis.


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## nitrocan (Aug 5, 2009)

brunson said:


> Johannes91 said:
> 
> 
> > brunson said:
> ...



(x1,y1) to (x2, y2) = sqrt( (x1-x2)^2 *+* (y1-y2)^2 )

It's basically the Pythagorean theorem. c = sqrt(a^2 + b^2)


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## brunson (Aug 5, 2009)

KYLE ALLAIRE DROPS BOMBS! said:


> If light slows down when it hits everything, please explain how it is getting here from 5 billion light years away through so much space dust and gravitational force. Please. http://www.hno.harvard.edu/gazette/1999/02.18/light.html
> edit: directed to ellis.


Why don't you go do some reading and educate yourself before trying to nit pick at everything you don't understand. 

The speed of light through a medium other than a vacuum is less that than of the speed of light through a vacuum. When light passes from a vacuum to air, it slows down; from air to water, it slows, from air to glass, it slows down. When it goes from glass or water to air, it speeds up; when it goes from air to a vacuum it speeds back up.

The article you link to describes a material that slows down light a lot more than anything else known before. When the light leaves that material it doesn't continue moving through the air at 38 miles an hour, it returns to its normal speed.


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## JBCM627 (Aug 5, 2009)

KYLE ALLAIRE DROPS BOMBS! said:


> brunson you sound pretty confused buddy.


I don't think he's confused. Ever heard the term 'index of refraction' ? Wait, Poe's Law.


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## vvtopkar (Aug 5, 2009)

@Kyle
Sorry to say this, but Brunson is a really brilliant guy that absolutely knows what he is talking about.

On another note, while we are talking about the speed of light:

Imagine a record turntable. In the case of any rotating disk, a point on the inside of the disk travels slower than a point on the edge of the disk. What if the center of a record was traveling at the speed of light, at what rate would the edge of the disk travel at?


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## Johannes91 (Aug 5, 2009)

vvtopkar said:


> What if the center of a record was traveling at the speed of light, at what rate would the edge of the disk travel at?


It wouldn't travel at all because the record would break.


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## brunson (Aug 5, 2009)

Hardly brilliant, just educated.


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## vvtopkar (Aug 5, 2009)

Johannes91 said:


> vvtopkar said:
> 
> 
> > What if the center of a record was traveling at the speed of light, at what rate would the edge of the disk travel at?
> ...



Would the edge break at the point it reaches the speed of light since the center is still accelerating?


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## JBCM627 (Aug 6, 2009)

vvtopkar said:


> Johannes91 said:
> 
> 
> > vvtopkar said:
> ...



It would break well before the edge reached those speeds due to centrifugal force. If you want to ignore that, the disk would break long before the edge reached the speed of light due to length contraction. If you had an unbreakable unbendable disk, you wouldn't be able to move it at all.


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## Horst2104 (Aug 6, 2009)

hahaha, this thread is hillarious  
after 3 years of studying physics i know that some things are hard to believe if you hear them for the first time, but u'll get used to it 

heres sth to think about:
imagine a wall with an infinite height falls over in your direction: does it make sense to run away ? 

mfg
manu


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## JBCM627 (Aug 6, 2009)

Horst2104 said:


> heres sth to think about:
> imagine a wall with an infinite height falls over in your direction: does it make sense to run away ?


is it infinitely wide?


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## Kian (Aug 6, 2009)

JBCM627 said:


> Horst2104 said:
> 
> 
> > heres sth to think about:
> ...



Hmm. I'm not sure it matters for his question. I guess I would say it doesn't matter if it runs away, because no matter how far away from the wall you are, it should never crush you, because it would need to fall an infinite distance to get there. I'm unsure of this answer, but it seems to make sense to me.


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## JBCM627 (Aug 6, 2009)

Kian said:


> Hmm. I'm not sure it matters for his question. I guess I would say it doesn't matter if it runs away, because no matter how far away from the way you are, it should never crush you, because it would need to fall an infinite distance to get there. I'm unsure of this answer, but it seems to make sense to me.


Yeah, I just thought of that too. But that brings up the question, can an infinitely tall wall fall over at all? I guess it really depends on what assumptions you make about the wall.


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## Johannes91 (Aug 6, 2009)

JBCM627 said:


> But that brings up the question, can an infinitely tall wall fall over at all?


My first thought was "Can an infinitely tall wall even exist?".


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## Tim Reynolds (Aug 6, 2009)

JBCM627 said:


> But that brings up the question, can an infinitely tall wall fall over at all?



My first thought was "hehehe there's a lot of rhyming words in that sentence"

Well let's see...if you're further away, then the angle between the wall and the floor is smaller, so it's been falling for longer, so it's going faster. But the whole infinite thing suggests it's probably infinitely massive, so you might be out of luck anyway...

I could try to actually set up some equations and send L to infinity, but I'm too lazy to do a differential equation right now.


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## imaghost (Aug 6, 2009)

The wall would never fall over, you could live your life with it falling and would never complete the fall. The top of it would be not be going faster than the speed of light, so even if it was, it would take an astronomical number of astronomical numbers of years to actually complete the fall.


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## Kian (Aug 6, 2009)

imaghost said:


> The wall would never fall over, you could live your life with it falling and would never complete the fall. The top of it would be not be going faster than the speed of light, so even if it was, it would take an astronomical number of astronomical numbers of years to actually complete the fall.



Uhh. No. It would never be able to fall. There is no amount of time at any speed where traveling an infinite distance is possible.

Obviously no such wall can exist, so the question poses a lot of problems, it's really a paradox.


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## watermelon (Aug 6, 2009)

Horst2104 said:


> hahaha, this thread is hillarious
> after 3 years of studying physics i know that some things are hard to believe if you hear them for the first time, but u'll get used to it
> 
> heres sth to think about:
> ...



To clarify:

1) Is the wall infinitely wide as well, or does it have a finite width?
2) Is the mass density of the wall uniform, or is it distributed in such a way that the wall has finite mass?


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## imaghost (Aug 6, 2009)

Kian said:


> imaghost said:
> 
> 
> > The wall would never fall over, you could live your life with it falling and would never complete the fall. The top of it would be not be going faster than the speed of light, so even if it was, it would take an astronomical number of astronomical numbers of years to actually complete the fall.
> ...



the point was that the infinite part actually was a number and did not go on forever. To us it would be an infinite distance, but it could stop, we just don't know yet. That was the point I was getting across. Of course, it is impossible to have an infinite distance between two things.


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## Horst2104 (Aug 7, 2009)

hi,

there were no assumptions at the beginning when i discussed this with some friends, so theres no answer that is wrong or right...

back to physics....

and the example of the muons hitting the surface of the earth:

while the particles accelerated in the LHC "only" will have the energy of a moving fly, we detect particles in the cosmic radiation, that have energies which compare to a really hard served tennis ball 

mfg


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## brunson (Aug 7, 2009)

<offtopic>I heard back from Kyle after a PM. This was apparently not him posting. He apologizes and is changing his password.</offtopic>


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## Carson (Aug 7, 2009)

watermelon said:


> Horst2104 said:
> 
> 
> > hahaha, this thread is hillarious
> ...



I suppose my mind instantly steers toward the logic in things as opposed to physics... Of what material is this wall composed? I don't think I would run away from a wall composed entirely of silly string.


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## imaghost (Aug 7, 2009)

Carson said:


> watermelon said:
> 
> 
> > Horst2104 said:
> ...


i am sure you would if it would kill you, if it's 20000000 feet thick, it would probably kill you if it happened to land on you.


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## mr.onehanded (Aug 14, 2009)

I love cubing because of all the smart people.


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## Si1v3rx51ay3r (Aug 14, 2009)

There was a test that was made to prove that time slow down when you go at very high speeds.

It was this - -

= = Get 2 clocks (set at exactly the same times)

= = Put one on a jet and one on the ground

= = Make the jet (with the clock) fly really fast...and stuff

= = Come back and.....one clock is a few seconds ahead/behind!!


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