# How does time stop at C?

## Main Question or Discussion Point

I never understood how time can slow down as you reach the speed of light then it stops...

I see time as a measurement by a mechanical clock. One second will always be one second.

My ap physics teacher said they did this experiment. They took a photon or something with a very small half-life. They shot these across a measured distance x and predicted that only like 2% of them should be left when they reach impact or whatever. v=d/t, them knowing the initial velocity and distance, the time calculated showed a ton of decay. But there was 98% left, which they concluded time stopped...

Ya anyways is it the process in which it is decaying that is lowing down, not time itself? Can someone clarify this for me? Like is you traveled at the speed of light, someone on earth with a stop watch would read 10min, so would your watch right? I need understanding ahh!

I have tons of questions, but it is late!

Thanks

## Answers and Replies

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rbj
as one person (with a clock) whizzes past another at very high speed, they both measure the speed of the very same beam of light to be the same value, even when they are moving relative to each other.

the normal textbook explanation of time dilation uses a "light clock" consisting of a burst of light bouncing back and forth between two parallel mirrors whose plane are parallel to the direction of motion (from the perspective on one observer) which means that the path the light is boucing back and forth is perpendicular to the direction of motion.

now if both persons, the one with the light clock moving past a "stationary" observer at high speed, and the "stationary" observer saw the "ticking" of this light clock as the same rate, then for the "stationary" observer, he would have to see the speed of light to be faster than the "moving" observer because it would have a component of c going up and down and a component of v going forward, giving you a diagonal speed of $\sqrt{c^2+v^2} \ge c$. but that contradicts the axiom of Special Relativity that all observers must see the speed as the same.

so, instead, the diagonal velocity is c and, since the forward component is still v, then the "stationary" observer sees the up and down component of the speed to be $\sqrt{c^2-v^2} = c \sqrt{1-v^2/c^2}$ which is slower than what the moving observer sees for the up/down speed of light (which is c). but the distance between the mirrors are the observed by both observers as the same (that distance is perpendicular to the direction of motion and has no reason to be observed differently), so the "stationary" observer has to see the rate of ticking of the light clock to be a factor $\sqrt{1-v^2/c^2}$ slower than the rate of the "moving" observer.

It is time itself which slows down, at least comparitively. However you cannot say "such and such happens at c" since you can never get there, you can only discuss what happens as you approach c.

The experiment you describe isn't something that can be done with photons to my knowledge, photons always travel at c (whatever c might be in the particular medium). One classical example of the effect you're talking about is the muons which are created by cosmic ray impacts in the Earth's upper atmosphere. Muons decay in an extremely short ammount of time, so quickly that they should have never been able to make it down to the Earth's surface. They are fairly common, however, and this is because when they are created by the collision in the upper atmosphere they have a very large velocity. We on the earth see them taking some ammount of time to travel from the upper atmosphere down to our detectors, however for the muon's own internal clock only a small fraction of that time has elapsed.

russ_watters
Mentor
physicscrap said:
Ya anyways is it the process in which it is decaying that is lowing down, not time itself? Can someone clarify this for me?
Well, if you observe the same phenomena with a half dozen different types of clocks, it is probably safe to say that it isn't coincidental clock effects, but time itself that is affected.

physicscrap said:
I never understood how time can slow down as you reach the speed of light then it stops...

I see time as a measurement by a mechanical clock. One second will always be one second.

My ap physics teacher said they did this experiment. They took a photon or something with a very small half-life. They shot these across a measured distance x and predicted that only like 2% of them should be left when they reach impact or whatever. v=d/t, them knowing the initial velocity and distance, the time calculated showed a ton of decay. But there was 98% left, which they concluded time stopped...

Ya anyways is it the process in which it is decaying that is lowing down, not time itself? Can someone clarify this for me? Like is you traveled at the speed of light, someone on earth with a stop watch would read 10min, so would your watch right? I need understanding ahh!

I have tons of questions, but it is late!

Thanks
Have you ever tried to synchronize two clocks that would move with speed c relative to each other?

Well what rbj explained to me was kind of confusing.

I still don't understand... well what exactly is time?

If you are approaching the speed of light, you are doing so for a period of time. Like you are superman flying and approaching c, while you are counting 1, 2, 3, 4.... so the measurement of time is the same as it would be a guy standing still counting.

Confusing. I just need someone to explain it to me logically or something. I am a visual learner, so make it visual :)

Thanks

pervect
Staff Emeritus
physicscrap said:
Well what rbj explained to me was kind of confusing.

I still don't understand... well what exactly is time?

If you are approaching the speed of light, you are doing so for a period of time. Like you are superman flying and approaching c, while you are counting 1, 2, 3, 4.... so the measurement of time is the same as it would be a guy standing still counting.

Confusing. I just need someone to explain it to me logically or something. I am a visual learner, so make it visual :)

Thanks
You might try "Al's relativistic adventures", the winner of the (edit) 2005 Pirelli award. It can be found at

http://www.onestick.com/relativity/

(and possibly other places as well, try google).

It's very visual, and it has a "quiz" feature to help you see if you've understood it.

But you'll need a flash player and a fairly high-speed connection, according to the website.

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robphy
Homework Helper
Gold Member
Here's something visual [and animated]
http://www.phy.syr.edu/courses/modules/LIGHTCONE/LightClock/ [Broken]

(pervect, that's 2005... not 1995)

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pervect
Staff Emeritus
robphy said:
Here's something visual [and animated]
http://www.phy.syr.edu/courses/modules/LIGHTCONE/LightClock/ [Broken]

(pervect, that's 2005... not 1995)
I guess I'm stuck back in the 90's :-( - anyway I'll fix the post to give the correct date.

What did you think of the presentation, by the way? I recalll that you contributed to the contest. I remember thinking that I had a few minor reservations about the way some of the material in the award-winner was presented, but that on the whole I thought it was very worthwhile.

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rbj
physicscrap said:
Well what rbj explained to me was kind of confusing.
yeah, it wasn't the best explanation possible. Al's Relativistic Adventures is a good illustration.

I still don't understand... well what exactly is time?
it's how fast the light clock ticks.

If you are approaching the speed of light, you are doing so for a period of time. Like you are superman flying and approaching c, while you are counting 1, 2, 3, 4.... so the measurement of time is the same as it would be a guy standing still counting.
oh no, as Superman is counting 1,2,3,4 it sounds like "wwwwuuuuunnnn, ttttoooooooooo, thhhhhhrrrrreeeeee, fffooooouuuuurrrrr" to me as he whizzes by. but it sounds like 1,2,3,4 to Superman.

Confusing. I just need someone to explain it to me logically or something. I am a visual learner, so make it visual :)

Thanks
if you still have questions after seeing Al's adventure, i'll try to spell it out again with some kinda different language.

Imagine counting, from any outside point, the swings of a pendulum bob as time. The time may vary according to observer-bob relative velocity, but at least its passage is non-zero.

Then imagine riding on the bob and trying to count time by the bob alone. This seems anomalous, but actually demonstrates that the relativity of standard bob speed vs standard bob speed results in static signaling.

MathematicalPhysicist
Gold Member
physicscrap said:
I never understood how time can slow down as you reach the speed of light then it stops...

I see time as a measurement by a mechanical clock. One second will always be one second.

My ap physics teacher said they did this experiment. They took a photon or something with a very small half-life. They shot these across a measured distance x and predicted that only like 2% of them should be left when they reach impact or whatever. v=d/t, them knowing the initial velocity and distance, the time calculated showed a ton of decay. But there was 98% left, which they concluded time stopped...

Ya anyways is it the process in which it is decaying that is lowing down, not time itself? Can someone clarify this for me? Like is you traveled at the speed of light, someone on earth with a stop watch would read 10min, so would your watch right? I need understanding ahh!

I have tons of questions, but it is late!

Thanks
let's see, a time measured by a mechanical clock has a constant motion in comparison to light is also constant, but what really is fascinating that perhaps you neglected to mention is how do you observe that light motion doesn't have any time elapsed.
well this is (as i can rememeber) a convention that was made in order to make sense to the phenomona of time contraction, i don't think they can observe that light motion is absent from time.

anyway, time is man made, so it's not impossible that nature doesn't see it fit, in the light case.

Alright I just watched Al's Adventures and have some questions.

Why can't a mass reach the speed of light or beyond? How does something seem squished relative to you if the ship is going at 99.5% of c?
Also, they use a clock measured by a photon bouncing between two mirrors, forming a second. I understand how that time slows down. But lets say you use a mechanical clock with gears, how does that slow down? It doesn't right, so time actually does not slow down, but the photon just takes longer to form a second for that particular clock. And how does one's brain function slow down. If you approached c, and the clock slowed down, you would notice that you are bouncing your ball faster. How do you think slower???

Also, when Al only took two years to travel to and back, it was only two years according to HIS clock, which is affected by his speed due to it being measured by a photon. But the actual time was 20 years, but Al thought it was 2. Is this correct? Furthermore, how can something be massless?

It gave me info that I already knew, but did not answer my questions in detail.

pervect
Staff Emeritus
physicscrap said:
Alright I just watched Al's Adventures and have some questions.

Why can't a mass reach the speed of light or beyond? How does something seem squished relative to you if the ship is going at 99.5% of c?
An object cannot reach the speed of light because velocities do not add linearly. Velocities do not add linearly because space and time get "squished" by motion.

"Why" space and time get squished by motion doesn't really have an answer - we simply observe that it happens. Specifically, we observe that the speed of light is constant for all observers, and from this observation we infer that space and time must get squished in the manner which is described in "Al's relativistic adventures" in order to explain these observations.

The detailed velocity formula addition in SR is

vtotal = (v1+v2)/(1+v1*v2/c^2)

Thus .9c + .9c = 1.8/1.81 c

If you add up ANY NUMBER of velcities, v, which are less than c, the result will still be less than c.

.9c + .9c + .9c + .9c + .9c .... + .9c

for any finite number of terms n

is less than c.

Also, they use a clock measured by a photon bouncing between two mirrors, forming a second. I understand how that time slows down. But lets say you use a mechanical clock with gears, how does that slow down? It doesn't right, so time actually does not slow down, but the photon just takes longer to form a second for that particular clock.
We observe that all clocks slow down by the same amount. If they didn't, we wouldn't see the speed of light as being constant, which is what started the whole theory.

Our most accurate clocks nowadays are made out of atoms, not gears, but they keep the same time as clocks with gears do. Note that atoms and gears are both held together by electomagnetic forces, the same forces that mediate light.

Back in Einstein's day, they didn't have atomic clocks, the best clocks were based on gears and pendulums(!). But the theory applies to any sort of clock.

Relativistic effects are pronounced enough that we can see the effect of relativistic time dilation on the lifetime of short-lived particles like muons. Fast moving muons live longer than slow moving ones. This has been observed both with cosmic muons, and muons in accelerators.

The mechanism of muon decay is not even electromagnetic, so we can see that the concept of "time" slowing down applies even to clocks that are based on nuclear phenomenon and not E&M phenomenon.

And how does one's brain function slow down. If you approached c, and the clock slowed down, you would notice that you are bouncing your ball faster. How do you think slower???
I think you missed the point of the illustration :-(. If your brain slowed down, and your body slowed down, right along with the ball, if _everything_ slowed down exactly the same amount, you wouldn't notice anything. Which is the main point of that particular part of the animation.

Also, when Al only took two years to travel to and back, it was only two years according to HIS clock, which is affected by his speed due to it being measured by a photon. But the actual time was 20 years, but Al thought it was 2. Is this correct?
Al's mechanical clock, Al's atomic clock, Al's brain, Al's light clock, and Al's bouncing ball all measured two years during his journey.

This means that by any means you can measure, Al "really" experienced two years.

The people on the ground also "really" experienced 20 years.

These two statemetns are not contradictory.

Furthermore, how can something be massless?
When it's mass is zero, an object is massless. (I've never understood why this would be a sticking point with anyone.)

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pervect said:
An object cannot reach the speed of light because velocities do not add linearly. Velocities do not add linearly because space and time get "squished" by motion.

"Why" space and time get squished by motion doesn't really have an answer - we simply observe that it happens. Specifically, we observe that the speed of light is constant for all observers, and from this observation we infer that space and time must get squished in the manner which is described in "Al's relativistic adventures" in order to explain these observations.

The detailed velocity formula addition in SR is

vtotal = (v1+v2)/(1+v1*v2/c^2)

Thus .9c + .9c = 1.8/1.81 c

If you add up ANY NUMBER of velcities, v, which are less than c, the result will still be less than c.

.9c + .9c + .9c + .9c + .9c .... + .9c

for any finite number of terms n

is less than c.

We observe that all clocks slow down by the same amount. If they didn't, we wouldn't see the speed of light as being constant, which is what started the whole theory.

Our most accurate clocks nowadays are made out of atoms, not gears, but they keep the same time as clocks with gears do. Note that atoms and gears are both held together by electomagnetic forces, the same forces that mediate light.

Back in Einstein's day, they didn't have atomic clocks, the best clocks were based on gears and pendulums(!). But the theory applies to any sort of clock.

Relativistic effects are pronounced enough that we can see the effect of relativistic time dilation on the lifetime of short-lived particles like muons. Fast moving muons live longer than slow moving ones. This has been observed both with cosmic muons, and muons in accelerators.

The mechanism of muon decay is not even electromagnetic, so we can see that the concept of "time" slowing down applies even to clocks that are based on nuclear phenomenon and not E&M phenomenon.

I think you missed the point of the illustration :-(. If your brain slowed down, and your body slowed down, right along with the ball, if _everything_ slowed down exactly the same amount, you wouldn't notice anything. Which is the main point of that particular part of the animation.

Al's mechanical clock, Al's atomic clock, Al's brain, Al's light clock, and Al's bouncing ball all measured two years during his journey.

This means that by any means you can measure, Al "really" experienced two years.

The people on the ground also "really" experienced 20 years.

These two statemetns are not contradictory.

When it's mass is zero, an object is massless. (I've never understood why this would be a sticking point with anyone.)
That didn't help lol.

How could a physical mass, such as you and your ship, be physically squished? That seems impossible. Also, if you are in space, with no resistance, and have a ton of power, how do you not reach c or past? Of course you said because of being squished which makes no sense. Also, light would not seem to be going at c if you were going 1/2 its speed. Like if you were driving at 50mph, the car that is going 100mph seems to be going 50mph faster, not 100mph. Again, you said space and tiem is squished which i don't understand. I just don't understand.

I also don't understand how the universe could be here. Since something has to make something, we can't exist, but we do. What made matter? what made that thing that made matter? etc... it is infinit, which is impossible for us to be here. ahhhhhh too confusing.

physicscrap said:
How could a physical mass, such as you and your ship, be physically squished? That seems impossible.

(and other questions...)
It does seem that way, but it isn't. Keep in mind that from the perspective of the moving object everything is normal, it's everyone else who are squished.

If you accept the fact that light must travel at the same speed in all inertial reference frames then all of these effects which we have discussed here are logical conclusions which must be true, there's simply no avoiding it.

Measuring the speed of light as being constant is an experimental fact, it's been measured to a very high degree of accuracy. After that everything else falls into place if you're willing to work through the logic, all these consequences such as time running more slowly and distances being measured differently are also experimentally verified to a high degree of accuracy.

Edit: By the way, it's a good thing that you're resisting all this. Special Relativity is usually the first instance in physics where people encounter an idea that simply goes against everything they've ever known to be true. Deep in our bones we "know" that velocities add linearly, we "know" that moving observers do not see time or distance any differently than we do. These things have been true for all of our lives, we've never encountered anything in our daily experiences which would indicate otherwise. Fact of the matter is that the only reason we "know" those things is because we generally travel extremely slowly. Even with cars the largest relative velocity I've ever had with respect to someone else is about 160mph or so.

Do not feel discouraged because you don't feel ready to accept these strange ideas, believe me when I say that it literally took me months for it all to soak in when I was first learning this stuff. If you keep plugging away at it and think about the concepts, work out the thought experiments, calculate some numbers for yourself, etc. you will eventually come to understand why everything we're saying must be true. It's just a bit of a journey to get to that point

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robphy
Homework Helper
Gold Member
pervect said:
What did you think of the presentation, by the way? I recalll that you contributed to the contest. I remember thinking that I had a few minor reservations about the way some of the material in the award-winner was presented, but that on the whole I thought it was very worthwhile.
I thought the presentation was good. It was creative and effective for the target audience.... but I think I liked the physics better in Ehrlich's presentation (see the blog entry https://www.physicsforums.com/blog/2005/12/03/pirelli-relativity-challenge-2005-winners-announced/ [Broken] ). In my opinion, however, the physics presented in these winning entries is rather ordinary and superficial. I would have been more impressed with (say) a multimedia presentation emphasizing more concrete operational methods as done in the little books by Bondi and by Geroch. I tried to do this in my attempt... but I didn't realize that it had to have more entertainment value.

pervect said:
When it's mass is zero, an object is massless. (I've never understood why this would be a sticking point with anyone.)
There's "massless" and "frictionless" ... but the connotation is different for "priceless". A related suffix is -free... as in trace-free. Maybe one should adopt the prefix zero- .

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dicerandom said:
It does seem that way, but it isn't. Keep in mind that from the perspective of the moving object everything is normal, it's everyone else who are squished.

If you accept the fact that light must travel at the same speed in all inertial reference frames then all of these effects which we have discussed here are logical conclusions which must be true, there's simply no avoiding it.

Measuring the speed of light as being constant is an experimental fact, it's been measured to a very high degree of accuracy. After that everything else falls into place if you're willing to work through the logic, all these consequences such as time running more slowly and distances being measured differently are also experimentally verified to a high degree of accuracy.

Edit: By the way, it's a good thing that you're resisting all this. Special Relativity is usually the first instance in physics where people encounter an idea that simply goes against everything they've ever known to be true. Deep in our bones we "know" that velocities add linearly, we "know" that moving observers do not see time or distance any differently than we do. These things have been true for all of our lives, we've never encountered anything in our daily experiences which would indicate otherwise. Fact of the matter is that the only reason we "know" those things is because we generally travel extremely slowly. Even with cars the largest relative velocity I've ever had with respect to someone else is about 160mph or so.

Do not feel discouraged because you don't feel ready to accept these strange ideas, believe me when I say that it literally took me months for it all to soak in when I was first learning this stuff. If you keep plugging away at it and think about the concepts, work out the thought experiments, calculate some numbers for yourself, etc. you will eventually come to understand why everything we're saying must be true. It's just a bit of a journey to get to that point
I accept that light travels at the same speed. But how does a fast moving person view the light at the speed of light? I would think that it would seem slower relative to the moving person.

I understand that distances are shorter when traveling close to c. Because time is slower, thus calculating distance using d=vt the distance is less then measured by a normal moving person.

But again, I am not sure about time. How does one's mental thinking slow down? moving close to c in space makes that person feel normal. So that person would think normal, and thus bounch his/her ball at the same pace of a second if that person were NOT refering to a clock.

*just thought of this* Ok you know that the light clock with the ship is traveling close to c. So the photon has to bounch extra distance thus slowing time. But refering to the ball bouncing, doesn't the ball have to travel a diagnal distance such as the photon? same concept right? That makes no sense. What I mean is that if the photon is maintaining the same speed as the ship, could it just bounch in a straight line? ahhh I am having trouble thinking this through.

EDIT: When time theoretically slows down, and so does everything else, does the human body biologically slow down so you ACTUALLY don't age as much, or you just don't age as much relative to time? hmm

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MathematicalPhysicist
Gold Member
pervect said:
An object cannot reach the speed of light because velocities do not add linearly. Velocities do not add linearly because space and time get "squished" by motion.
what do you mean by not add linearly?
i think you can add velocities by simple algebraic arithematics and vector calculus which is linear (if you don't take into consideration non inertial accelerating motion which is not linear).

robphy
Homework Helper
Gold Member
loop quantum gravity said:
pervect said:
An object cannot reach the speed of light because velocities do not add linearly. Velocities do not add linearly because space and time get "squished" by motion.
what do you mean by not add linearly?
i think you can add velocities by simple algebraic arithematics and vector calculus which is linear (if you don't take into consideration non inertial accelerating motion which is not linear).
Let VBA denote the relative [spatial] velocity of observer B with respect to observer A.

In relativity,
VCA =/= VCB + VBA.
Thus, the spatial velocities don't add linearly. (Part of the problem is that you are trying to relate spatial velocity vectors in different inertial frames of reference, where their notions of space don't coincide. So, one has to project down into the respective spaces. Vector methods do work... but you must use 4-vectors [for example, see my post, #5, in https://www.physicsforums.com/showthread.php?t=73582].)

("Addition of velocities" should really be called "Composition of velocities".)
What does add linearly is the rapidity, where VBA=c tanh(rapidityBA)...
then
VCA=c tanh(rapidityCA)=c tanh(rapidityCB+rapidityBA),
which can be rewritten using the hyperbolic-trig identity for the tanh of a sum to obtain the velocity composition formula:
VCA=( VCB + VBA )/(1 + VCBVBA/c2 )

pervect
Staff Emeritus
loop quantum gravity said:
what do you mean by not add linearly?
i think you can add velocities by simple algebraic arithematics and vector calculus which is linear (if you don't take into consideration non inertial accelerating motion which is not linear).
By "addition of velocities", I mean that if A is going at a velcity of .9c relative to B (a statement that is true in either A's frame or B's frame), and that B is going at a velocity of .9c relative to C (a statement that is true in either B's frame or C's frame), then A's velocity relative to C is NOT 1.8 c (the sum). Rather it is given by the formula I posted earlier, which is not linear.

There's more detail in
http://math.ucr.edu/home/baez/physics/Relativity/SR/velocity.html" [Broken]

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pervect
Staff Emeritus
physicscrap said:
I accept that light travels at the same speed. But how does a fast moving person view the light at the speed of light? I would think that it would seem slower relative to the moving person.
I'm not sure why you think that.

I understand that distances are shorter when traveling close to c. Because time is slower, thus calculating distance using d=vt the distance is less then measured by a normal moving person.

But again, I am not sure about time. How does one's mental thinking slow down? moving close to c in space makes that person feel normal. So that person would think normal, and thus bounch his/her ball at the same pace of a second if that person were NOT refering to a clock.
Imagine a computer running a piece of software that's artifically intelligent. Now suppose we slow the computer down by reducing it's clock speed. The rest of the world would seem to go by faster from the "viewpoint" of the computer. The unit of time for the computer would be one CPU cycle, which would be a "tick" of its internal clock.

Replace the computer with a person. If we slowed a person down, and left the rest of the world running normally, the world would seem fast to the slowed down person. (t's easier to visualzie this with a computer, because a computer has a clock that it's easy to imagine slowing down, it's a bit harder with a person, but the idea is the same.)

But if we slow *everything* down at the same rate, neither the computer nor the person would notice anything at all.

The point is that time always seems to pass normally for everyone, regardless of their velocity, from their own viewpoint. However, when you have two people moving at different speeds, their perception of time is different. Each person thinks that the other person has been slowed down (and crushed).

G01
Homework Helper
Gold Member
physicscrap said:
I accept that light travels at the same speed. But how does a fast moving person view the light at the speed of light? I would think that it would seem slower relative to the moving person.
Have you heard of Maxwell's equations? Well, one of them predicts that the speed of light should be equal to c. This caused alot of confusion. Everyone wondered when it would travel c relative to someone else. Would I see light going by me at c if i was at rest, or if i was moving 100mph, or 200mph, which one was it. The equation didn't say what speed you had to travel to see light go by you at the speed of light. This is because it doesn't matter. Einstein postulated that everyone, no matter how fast they were travelling, would see light pass them at speed c. This didn't make any sense everyone thought! How can this be? Well Einstein had an explanation. (see next paragraph)

I understand that distances are shorter when traveling close to c. Because time is slower, thus calculating distance using d=vt the distance is less then measured by a normal moving person. But again, I am not sure about time. How does one's mental thinking slow down? moving close to c in space makes that person feel normal. So that person would think normal, and thus bounch his/her ball at the same pace of a second if that person were NOT refering to a clock.
Einstein realized the only way for everyone to see light pass them by at the speed c, no matter how fast they were travelling, was if the ammount of time and space the person experienced was less. If the distance became less, and less time passed then a person moving would still be able to see a beam of light go by them at c. (since v=d/t, in order for v to stay the same d and t have to change also). This is just the way it is. It is just how nature works. And it has beenexperimentally proven

You can't think of it as a person's brain slowing down, or the ball slowing down, or the gears in the clock slowing down. They still tick once every second. Its just that it takes longer for one second to pass. It is not something mechanical, or biological, TIME ITSELF moves slower. Thus if you were moving fast, not only would the clocks slow compared to someoone at rest, but you would also AGE LESS than the person at rest. If you were moving fast enough so that you experienced two years while someone at rest experienced 20 years, you can't say, "O well it was really 20 years." NO!! The time you experience is completely independent of other people. Both are right, you experienced 2 years, and the person a rest experienced 20, thats the way nature is.

*just thought of this* Ok you know that the light clock with the ship is traveling close to c. So the photon has to bounch extra distance thus slowing time. But refering to the ball bouncing, doesn't the ball have to travel a diagnal distance such as the photon? same concept right? That makes no sense. What I mean is that if the photon is maintaining the same speed as the ship, could it just bounch in a straight line? ahhh I am having trouble thinking this through.
The ball follows a diagonal path when seen from the outside of the ship,
and bounces straight when seen from inside of the ship. Both of these statements are correct. Its all relative to where you are looking from, just like how much time and distance a person experiences. Hence the name, Theory of RELATIVITY.

EDIT: When time theoretically slows down, and so does everything else, does the human body biologically slow down so you ACTUALLY don't age as much, or you just don't age as much relative to time? hmm
Yes, if you moved fast enough, you would be able to live millions of years COMPARED TO SOMEONE AT REST, when you only experienced 10 years. Remember though the measurment of a million years is just as correct as the measurment of 10 years.

G01 said:
Have you heard of Maxwell's equations? Well, one of them predicts that the speed of light should be equal to c. This caused alot of confusion. Everyone wondered when it would travel c relative to someone else. Would I see light going by me at c if i was at rest, or if i was moving 100mph, or 200mph, which one was it. The equation didn't say what speed you had to travel to see light go by you at the speed of light. This is because it doesn't matter. Einstein postulated that everyone, no matter how fast they were travelling, would see light pass them at speed c. This didn't make any sense everyone thought! How can this be? Well Einstein had an explanation. (see next paragraph)

Einstein realized the only way for everyone to see light pass them by at the speed c, no matter how fast they were travelling, was if the ammount of time and space the person experienced was less. If the distance became less, and less time passed then a person moving would still be able to see a beam of light go by them at c. (since v=d/t, in order for v to stay the same d and t have to change also). This is just the way it is. It is just how nature works. And it has beenexperimentally proven

You can't think of it as a person's brain slowing down, or the ball slowing down, or the gears in the clock slowing down. They still tick once every second. Its just that it takes longer for one second to pass. It is not something mechanical, or biological, TIME ITSELF moves slower. Thus if you were moving fast, not only would the clocks slow compared to someoone at rest, but you would also AGE LESS than the person at rest. If you were moving fast enough so that you experienced two years while someone at rest experienced 20 years, you can't say, "O well it was really 20 years." NO!! The time you experience is completely independent of other people. Both are right, you experienced 2 years, and the person a rest experienced 20, thats the way nature is.

The ball follows a diagonal path when seen from the outside of the ship,
and bounces straight when seen from inside of the ship. Both of these statements are correct. Its all relative to where you are looking from, just like how much time and distance a person experiences. Hence the name, Theory of RELATIVITY.

Yes, if you moved fast enough, you would be able to live millions of years COMPARED TO SOMEONE AT REST, when you only experienced 10 years. Remember though the measurment of a million years is just as correct as the measurment of 10 years.
Not to offend but I think that is complete utter bull****. I have gotten to the point where I can't really explain myself, but I will try again to emphasize my confusion.

The photon clock will go slower as you speed up, ok true. But time itself is the same no matter what. If I am standing still looking at my watch, or if I am on a nasa space shuttle looking at my watch, time is the same. "oh look it has been 10 minutes..." applies everywhere. How could your aging slow down, and how you said you could live for millions of years ok bull****. You get just as old and anyother Joe. Your body decays and whatnot.

If your are traveling at the speed of light, you feel normal like you are standing on earth, thus everything would function the same. Your bouncing ball would not bounce diagonally because it is at a constant speed with you and the ship(c). I do not understand how this is accepted as it makes absolutly no sense. a mechanical clock with gears and a battery will function at the normal second because it is not influenced by the speed in which it is traveling, thus time is the same. But relative to a photon clock, time will slow down, but does not mean it truly does.

You travel at the speed of light to a distant galaxy 10 light years away, it takes a total of 20years no matter what to go there and back and you will age 20 years.

Sorry if I sound like a narrow minded fool, but my mind cannot grasp what I consider nonsense.

"Sit down before facts like a child, and be prepared to give up every preconceived notion, follow humbly wherever and to whatever abysses Nature leads, or you shall learn nothing." - T.H. Huxley

There are a couple things you have to simply accept for now. The questions of why are either unknown or too complex to explain satisfactorily.

1) The speed of light is measured to be the same by all observers no matter how fast they're moving

2) Matter cannot accelerate to the speed of light. Stop saying "if you travel at the speed of light."

3) If someone is in a spaceship & he's moving very close to the speed of light, everything in the ship will be in slow motion. Time itself in the ship will be running slowly. The guy in the ship will see his clock working ok. This is a direct result of the first two points. It takes a while to see why, though.