# Speed of light...instantatious Travel??

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### #1 fatty_ashy

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Posted 14 April 2003 - 04:04 AM

Hi people, this is my first time here!! i'm glad there are people out here that like this kindda stuff...my frens say it's boring...oh dear, i'm ranting...

Erm, I was wondering if travelling at the speed of light actually means instant travel.

According the time dilation factor....let's say if we are actually travelling at the speed of light exactly. Basically that would mean the Time dilation factor is 1/0; dividing one by zero gives infinity doesn't it? that means if we are actually travelling at speed of light, in real time, we would be taking ___ lightyears, but if the time dilation factor is up to infinity, doesn't that sort of mean that time would hardly move in the ship? According to Length Contraction, millions of lightyears would just seem like a snap!!

Anyone has an idea of their own?

### #2 Tormod

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Posted 14 April 2003 - 04:47 AM

Hi! And a warm welcome to you.

I'm not sure I get your point. Travel at the speed of light _is_ travel at the speed of light, i.e. some 360,000 kilometers per second. Strange things happen at this speed, yes, like the conversion of matter into energy - which is why only energy travels at the speed of light (photons, for example). Instant travel would mean _faster than light_ travel, which would be impossible for any object that travels at a rate lower than the speed of light. That would be teleportation...which we recently discussed here.

Division by 0 does not get you an infinity, it gives you an error. Any calculation which gives you an infinity is probably not the best way to try to understand the Universe.

If what you say is true, however, then the light which comes from the Big Bang has never experienced any "time" in our sense of the word (ie, slow, forward motion of time). The light particles/waves would be much, much younger than the current age of the Universe.

But in fact, we observe light to be moving through space at a fixed speed, so it cannot be travelling instantly. Sorry...but feel free to show me that I'm wrong.

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### #3 fatty_ashy

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Posted 14 April 2003 - 06:36 AM

Ummm...i'm not sure if i was clear. i read from some website about time dilation.
Which means let's say IF i travel in a ship at 99% the speed of light, the time dilation factor is 7. erm, so if i'm in space for a year constantly travelling at that speed, and i land on earth; seven years would have passed on earth despite i aged only one year.
so if i AM travelling at the speed of light, i would have travel ____ light years to an observer, but it would be just a fleeting moment for me. am i wrong??

### #4 Tormod

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Posted 14 April 2003 - 10:42 AM

No, you are not wrong. But time dilation is a strange phenomenon. Einstein postulated that when two bodies move relatively to each other, both will observe that the other's clock slow down. If you travel to Alpha Centauri and back at the speed of light, while I stay on Earth, you might get back after my death while you yourself will only have aged a few years.

But remember that this is all theory...nothing material will ever reach the speed of light, because the energy needed to accelerate an object to that speed will crush the object and turn it into energy at an ever increasing rate. (This is an over-over-simplification). A starship will most likely never be able to reach a speed of 99% of the light speed.

I suggets you read the book "E=mc2, The Biography of an Equation", by David Bodanis. Or better yet, read "Relativity" by Albert Einstein. It's not that hard. Well, it is. But not. Get it?

This is also coverd in depth by Carl Sagan, Stephen Hawking, and many other cosmology writers. In "How to build a time machine" Paul Davies does a good job explaining the Time Dilation effect. It's full of paradoxes but it makes sense in some strange way.

Which I probably don't, sorry about that.

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### #5 paperclip

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Posted 16 April 2003 - 07:43 PM

Comment: Division by zero doesn't necessarily give you an error. If you take lim(x->0)+ [1/x] you'll get infinity, which is an acceptable mathematical answer. lim(x->0)- [1/x] gives you negative infinity. It's not an error, per se, but more an indeterminable state, unless the limit is defined.

But, as you said tormod, this doesn't have practical applications.

Quick question: If travel at the speed of light necessitates a passage of time somewhere, does travel through a wormhole do likewise? Since light speed is thought to be the "barrier" for all speed possible, then travelling through a wormhole would be instantaneous and circumvent this speed limit. So would the universe compensate by forwarding (or reversing?) time elsewhere?

-paperclip

### #6 administrator

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Posted 17 April 2003 - 02:05 AM

paperclip, you're right about the zero part, of course.

The wormhole thing: no, I don't see why the Universe needs to compensate. The speed limit is not broken. A wormhole is a tunnel through space-time, like I wrote above, just like a tunnel. You do not travel faster than light when you go through the wormhole, you simply go from point A to point B in a very short time. If you had travelled around the wormhole the trip would have taken you much longer.

It is always the traveller's reference frame we are talking about...the traveller never breaks any speed limits, because (the time it takes for him to travel from A to divided by (the distance he has covered) does NOT provide anything but a quite normal speed. See my tunnel analogy above.

Now, what you should really be asking is what is a wormhole and how can it create a tunnel in space-time.

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### #7 administrator

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Posted 17 April 2003 - 08:26 PM

Hey Fatty, I’m not a physicist, but I’ve reached the same conclusion as you from my limited studies. I only found this web site because I was looking to see if others were discussing the very issue you raised. I was delighted to find that I wasn’t alone. From what I can piece together, travel would be "instant" for an object traveling at light speed.

According to the relativistic effect known as “length contraction,” the length between to points in space for an object in motion is shorter than the length between the same two points in space for an object at rest. This is because for an object in motion, distance between two points shrinks by a factor of gamma.

At 95% of the speed of light (.95c), gamma is about 3.2. So if the distance between two points of space is 100 light years for an object at rest, then for an object traveling at 95% of the speed of light, the distance between those same two points in space is only 31.25 light years (100/ 3.2).

At 100% of the speed of light ©, gamma is infinite (0). Therefore, running the same mathematical equation, if the distance between two points in space is 100 light years for an object at rest, then for an object traveling at 100% of the speed of light, the distance between those same two points in space is zero (100/0).

So, I believe that you are exactly right. For an object traveling at light speed, travel from any to points in the universe is essentially “instantaneous” because, for that object, there is no distance between any two points in the universe.

Somebody please correct me if I am wrong.

### #8 syndicated

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Posted 18 April 2003 - 06:51 PM

"Length contraction" sounds like a pretty cool theory and everything, but doesn't the fact that it takes light approx. 8.5 minutes to reach earth from the sun completely disprove it? Light, although pure energy, has to travel that distance - as Tormod pointed out. This would imply that any background radiation left over from the big bang which we have observed is actually radiation which is being radiated right now by existing stars, pulsars blah blah blah...

It is beyond my understanding why this length contraction theory is still being used, if what we are observing today disproves it.

Ben

### #9 fatty_ashy

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Posted 18 April 2003 - 09:41 PM

Hi Ben...i was thinking about what you said. You mentioned Light takes approx 8.5 mins to reach earth. How does that disprove Length Contraction? What length contraction says, is that WE observe an object moving over a period over time, however, the object ITSELF feels as if less time has passed. Soooo, how does that go agaist Length Contraction?
Btw, Length contraction is part of Relativity. (i think)

### #10 syndicated

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Posted 19 April 2003 - 07:21 PM

I probably should have been clearer in what I said.
It was stated that for an object travelling at light speed the distance between any 2 points in 0, due to this length contraction theory. This would also suggest that since distance is 0, the time it takes to travel X distance at light speed would also be 0, Yes?
How can that be possible? EVERYTHING takes time. Otherwise it wouldn't matter, according to planck's time right?
We measure the distances in the universe by light years, the time it takes for light to travel that point to us. Taking time dialation into effect, sure, it takes less time for that light to reach us, but it still takes time and travels that distance, no matter if we're observing it, or the observer is travelling at the speed of light.

Maybe there is something I'm not understanding about this theory, but it just doesn't jive with me.

Ben

### #11 syndicated

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Posted 22 April 2003 - 10:46 PM

Judging by the fact that no one has responded, I have either said something really stupid, or really smart.
9 times out of 10, the stupid response seems to be the one that i say.... someone let me know!

### #12 fatty_ashy

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Posted 23 April 2003 - 03:26 AM

well syndicated...maybe you do not really understand what length contraction means.
For example, object A is moving at a very high speed and let's asumme his time dilation factor is 7. If he travels over the distance of 7 000 000 000km, time dilation says he would only experience 1/7 of the time past right? So does that mean he only travels 1000000000km? No, it does not. The person himself would only ObSERVE that he travelled only 1 000 000 000km, but in actual fact, he has travelled 7 times that amount.
So if one were to travel at the speed of light, let's say he travels for 50 light years, 50 years would have past outside the spaceship, but he would have only observed a moment. Similarily, the ship actually takes time to travel, but the passenger does not observe that time passing. Get it?? He actually takes that time to travel, but he does not notice it.
Sorry if i'm not very clear.

### #13 Tormod

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Posted 23 April 2003 - 11:03 AM

syndicated,

sorry that you didn't get an answer...it was Easter weekend and I'm sure people were a bit busy.

Here's a link to a simple page with a nice illustration showing length contraction:

http://www.glenbrook...specrel/lc.html

Tormod

### #14 sardonyx247

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Posted 06 July 2003 - 12:39 AM

Time is only relvent to the observer! If you see something moving at the speed of light YOU will think it is instantaneous, if you were deaf then you would think that the speed of sound was instantaneous too! A light year is how far it light TRAVELS in ONE YEAR. So you would be traveling very very fast but it will take TIME to get there.

### #15 fatty_ashy

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Posted 06 July 2003 - 09:08 PM

well said! That was exactly what I have been trying to say

### #16 alternative3

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Posted 08 July 2003 - 08:40 AM

my first post ...

i've been reading these forums off and on with a lot of interest and finally have two quick questions to ask ... (please pardon my ignorance of physics etc)

- If I were moving at the speed of light through deep space or whatever, would I get squished into a near-2D line? Would I survive?

- Aren't galaxies receding from each other at the speed of light suggesting that they are all moving at the speed of light? If so aren't we all already moving at the speed of light? How does the relativity theory explain this?

that's it

### #17 Tormod

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Posted 08 July 2003 - 03:42 PM

alternative3, welcome to our forums!

As for question 1, I don't have an answer at hand.

But question 2 is interesting. Where did you read that galaxies receed from each other at the speed of light? Think about it: if all the galaxies are moving away from each other at the speed of light, would we ever see light coming from _any_ galaxy?

Galaxies do not move at relativistic speeds (meaning speeds close to that of light). Some galaxies are even moving towards us. You can read more about the speed of galaxies here:
The Hubble Constant

Tormod