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The wall of light

Posted by: Gygantar - Mon Oct 04, 2010 3:25 am
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The wall of light 
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Post The wall of light   Posted on: Mon Oct 04, 2010 3:25 am
Ok, so chuck Yeager didnt die when crossing the speed of sound, what will happens to us if we cross the speed of light? Is it just another demon out of our imagination and nothing will happen? What are the serious theories and hypothesis?

Thank you! ^^

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Post Re: The wall of light   Posted on: Mon Oct 04, 2010 10:47 am
It's a physical limitation that no object with a mass can ever move faster than light because you would need infinite energy to even reach c.

That is until somebody finds a flaw in Einsteins theories and comes up with a more accurate description of the inner workings of our universe.

With that out of the way, there are some hypothesis on how to circumvent that fact by not actually moving faster than light but still reaching your destination "faster than light", for example by warping space-time itself like it is the case with the Alcubierre drive. However, none of those methods seem to be practically achievable in the foreseeable future.

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Post Re: The wall of light   Posted on: Sat Oct 09, 2010 1:48 am
Marcus Zottl wrote:
It's a physical limitation that no object with a mass can ever move faster than light because you would need infinite energy to even reach c.

That is until somebody finds a flaw in Einsteins theories and comes up with a more accurate description of the inner workings of our universe.

With that out of the way, there are some hypothesis on how to circumvent that fact by not actually moving faster than light but still reaching your destination "faster than light", for example by warping space-time itself like it is the case with the Alcubierre drive. However, none of those methods seem to be practically achievable in the foreseeable future.



Yes I actually saw an explanation of the Alcubierre drive, by the guy himself in fact. Its on Youtube. Thanks for the input! =D

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Post Re: The wall of light   Posted on: Sat Oct 09, 2010 1:46 pm
If you are the guy on the starship... you will preceive youself going faster than light. The 80 lightyear trip you are planning will only take an hour. Alas, it is an illusion. At those speeds time dilation becomes a major factor. Your clock wll be telling you, you are moving faster than the speed of light. Of course it will be relative... everyone elses clocks will say your clock is running slow, in fact very very slow. So you will be able to travel the 80 light years in an hour from your prespective from everyone elses it still takes 80 years for you to make that trip.

Btw Time dilation is confirmed. You can't put a probe on another planet if you don't factor in the slower clock speed your probe encounters during the trip. If you don't your probe will crash into/miss the planet. Don't believe me... ask nasa.


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Post Re: The wall of light   Posted on: Sat Oct 09, 2010 7:58 pm
Akkman wrote:
If you are the guy on the starship... you will preceive youself going faster than light. The 80 lightyear trip you are planning will only take an hour. Alas, it is an illusion. At those speeds time dilation becomes a major factor. Your clock wll be telling you, you are moving faster than the speed of light. Of course it will be relative... everyone elses clocks will say your clock is running slow, in fact very very slow. So you will be able to travel the 80 light years in an hour from your prespective from everyone elses it still takes 80 years for you to make that trip.

Btw Time dilation is confirmed. You can't put a probe on another planet if you don't factor in the slower clock speed your probe encounters during the trip. If you don't your probe will crash into/miss the planet. Don't believe me... ask nasa.



Very interesting! There is talk of a photonic drive that could allow you to go faster than lightspeed. But you have to prevent the effect on the astronauts. Or could we combine two technologies? A good running jump with a photonic drive and an actual "jump" with a jump drive or whatever?

I know its Sci-Fi vs real tech ! =D But its interesting to wonder! It would make astrogation look like a dragster race with a trampoline at the end! :P

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Post Re: The wall of light   Posted on: Mon Oct 11, 2010 8:48 am
Whoa, not so fast there. Time dilation is described by Einstein's special theory of relativity, but that very same theory says that anything with mass can not go faster than the speed of light. So what you are saying doesn't make sense.

In Newtonian mechanics, F delta_t = m delta_v, where F is a constant force applied to an object, delta_t is a period of time during which the force is applied, m is the object's (constant) mass, and delta_v is the total change in velocity of the object.

Apply a constant force of 1 Newton to a space ship with a mass of 3 kg for 6 seconds, and the ship's speed (as seen by an observer relative to which we're measuring it) will increase by (1 * 6) / 3 = 2 m/s.

Note that how big the speed difference is depends on the mass; apply the same force for the same amount of time to someone on a bicycle and someone in a lorry, and the cyclist will be going quite a bit faster, because it's lighter. The change in momentum (m * v) however, will be the same.

Now, according to Newtonian mechanics, you can simply keep pushing, and the momentum will keep increasing, with it the speed and off you go. Do it long enough, and you will be going faster than light.

Unfortunately, it turns out that Newton's theory is not complete. For every day velocities the error is so tiny that it couldn't be observed with the methods of Newton's time. The first hint we got was that the orbit of the planet Mercury didn't follow Kepler's laws for planetary motion exactly. It took quite a while for someone to figure out that there wasn't an additional planet throwing Mercury off-course, but that our theory of motion was incomplete.

That someone was of course Einstein, although the bit of the mathematics that is relevant here had been worked out several years previously by Lorentz.

In special relativity, the momentum of an object is not m * v, but m * gamma * v. This gamma is the so-called Lorentz factor, and is equal to 1 / (sqrt(1 - v^2 / c^2)), with v the velocity, and c the speed of light. With this equation we can see what happens for different values of v. If v is 0, then gamma is 1 / sqrt(1) = 1, and so everything looks just like in Newtonian mechanics. If v = c, that is, we are traveling at the speed of light, then gamma = 1 / sqrt(1 - 1) = 1 / 0. You cannot divide by zero mathematically, so according to the theory of general relativity, it's impossible to travel at the speed of light. (There is a special case if your mass is zero, for example when you're a photon, where m * gamma * v has a finite result, hence light can travel at the speed of light. To the great joy and relief of researchers and students alike, because it would have been a bit silly if light couldn't travel at the speed of light, but I digress ;-))

Another way of looking at it is that as you keep pushing your space craft, you keep increasing your momentum m * gamma * v, but more and more of that increase is taken up by gamma getting larger, so that v changes less and less as you get closer to the speed of light. If the observer-at-a-standstill were Newton, he would say that he saw you pushing, so that your momentum must increase, but he also saw your speed barely changing. In Newtonian mechanics, the only conclusion would be that if m * v is increasing, and v doesn't change, m must be increasing. So Newton would conclude that your mass was getting larger the faster you went! Sometimes, your ordinary constant mass m is referred to as your rest mass, and this virtual mass m * gamma as your relativistic mass.

The equations for time dilation also use gamma: if you are looking at a clock carried on a space ship moving at velocity v and compare it to one in your hand, you will observe the time between two ticks of the clock on the ship to be gamma times as long as the time your own clock takes. If the ship is standing still, there is no difference, if it's zipping by at half the speed of light, then its clock will seem to take 1/sqrt(1 - 0.5^2/1^2) = 1 / sqrt(3/4) ~ 1.15 times as much time as your clock does for a single tick. Interestingly, an observer on the space ship will see your clock go slower by the same amount.

And then, that spacecraft will look oddly squashed to you too, its nose-to-tail length will seem to have changed by 1/gamma to you, so that a 100m space ship will seem to be only 87m long if it's going by at half the speed of light. The people inside won't notice, as their rulers have shrunk by just as much, but if they look out the window, they will see you going by at half the speed of light, and you will seem rather thin to them!

Clearly, this theory is completely crazy, and should be disregarded. The problem is that every single experiment we've ever devised to show that it's wrong has confirmed it, so we're stuck with it :-).

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Post Re: The wall of light   Posted on: Mon Oct 11, 2010 9:36 am
Lourens, are you a teacher? Because that is possibly the best explanation of the special theory of relativity that I've ever read! :)

Btw:
"Whoa, not so fast there." Was probably the greatest opening for a post on that topic as well! :D

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Post Re: The wall of light   Posted on: Tue Oct 12, 2010 1:47 am
Thank you for the explanation! Although this is quite beyond my capacity to comprehend. LOL! I'll re-read it later. :P

Still, we need to test it, thats what I conclude. And testing will give us leads to get what we want: Light speed. =D

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Post Re: The wall of light   Posted on: Tue Oct 12, 2010 8:44 am
Gygantar wrote:
Thank you for the explanation! Although this is quite beyond my capacity to comprehend. LOL! I'll re-read it later. :P

Still, we need to test it, thats what I conclude. And testing will give us leads to get what we want: Light speed. =D


It has been tested (please read Lourens post!).

If (and its a very big if), speeds of light speed or more are possible, we, as a race, are some centuries away from developing the technology to do it, because that technology is so far away from our current understanding as to be almost magical. (With apologies to A.C.Clarke)


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Post Re: The wall of light   Posted on: Tue Oct 12, 2010 12:29 pm
Yes that was a very good exposition of relativity! Bravo Lourens.

We already have the concept of a couple of ways to "cheat" around relativity, its just that we don't have all of the pieces to make it technically possible. A lot of it centered on that we can't generate the energies required for most of them (which at this point is probably a good thing).


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Post Re: The wall of light   Posted on: Tue Oct 12, 2010 8:29 pm
JamesHughes wrote:

It has been tested (please read Lourens post!).


What I meant is I didnt have the time to read it well I was busy, I just scanned through the lines! English is my 2nd language also, thus making it harder to understand.

A+

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Post Re: The wall of light   Posted on: Tue Oct 12, 2010 10:27 pm
Thanks for the compliments ;-).

@Marcus: I work at the University of Amsterdam, but not in a teaching position, so no, I don't teach. I've been a teaching assistant for a few months during my computer science studies, and I've been explaining things to classmates all my life, that's pretty much it. I'm going to be doing a PhD though, and that usually means a bit of teaching as well, so hopefully I'll get a chance. I'm looking forward to it :-). Also, the opening was a fluke! I didn't even realise it until you pointed it out.

@Gygantar: Sure you can understand it. Just go slow and read it one sentence at a time, and think about it a bit. Yes, it's a bit more complicated than most stuff you read in the media these days, but that's because that stuff is the information equivalent to a cucumber: lots of volume, barely any calories. And English is my second language as well, so that's no excuse :-).

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Post Re: The wall of light   Posted on: Wed Oct 13, 2010 6:26 am
Or, you could just watch the video
http://www.youtube.com/watch?v=7Z7GtgfTZ6w

:?


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Post Re: The wall of light   Posted on: Wed Jun 08, 2011 2:46 am
@Gygantar: Sure you can understand it. Just go slow and read it one sentence at a time, and think about it a bit. Yes, it's a bit more complicated than most stuff you read in the media these days, but that's because that stuff is the information equivalent to a cucumber: lots of volume, barely any calories. And English is my second language as well, so that's no excuse :-).[/quote]


Well, maybe you're better at your second language than I am, ever thought of that?

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Post Re: The wall of light   Posted on: Wed Jun 08, 2011 8:59 pm
That could be. I'm very sure my French is worse than your English though :-). Again, just take it one sentence at a time, and if you get stuck, ask. We're more than happy to explain.

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