No no. I meant literally get squashed into a pulp and not "appear squashed to an observer".

Errrmmmm.... I'm not qualified either.....

Sure, except that to any observer, if you're truly moving at the speed of light, your length will be exactly zero. Your original statement was:


But you do look squashed to any person observing you, even when you travel at a constant speed, this time, being the speed of light.

Agreed (based on current theories).

This post has been edited by kmarc: Dec 21 2009, 11:04 PM

that's what i said.

my point, relating to TS, is that they dont get younger. meaning age was not reversed. if u depart at 20 years old, u will not get back at 19 years old. moving at or near lightspeed is not the fountain of youth .

Future theories might not make it true either; in fact it might end up being an impossibility

Else it'll bring up the question: Why haven't we seen anyone from the future yet?

Note: In the initial statement, I said that FTL is a theoretical impossibility. I said this in the context of special relativity, where an inspection of the equation for the momentum of a particle in special relativity would give contradictions if you allowed a particle with mass to travel at the speed of light, i.e. it is impossible to take an object with mass, travelling at less than the speed of light relative to an observer, and then accelerating it to the speed of light, and hence you can't expect such an object to ever travel faster than light, since it can never pass the speed of light in the first place. There was no General Relativity brought into the discussion at all.

Note 2: I did more reading; the metric introduced by Alcubierre doesn't allow for FTL travel either, or travelling at the speed of light for particles with mass.

This post has been edited by bgeh: Dec 22 2009, 04:36 AM

Errr... the "Time directive" maybe? They are here but invisible maybe? Haha... more sci-fi.....

Yes, FTL is theoretically impossible based on current theories. I have no arguments with that. However, my argument is, why should FTL be limited to current theories? As I said earlier, faster than light travel just means you travel at >300k km/s by whichever means possible. If you could travel at 300k km/s in your "bubble" when the bubble is doing the "travelling" but your spaceship and the space within the bubble is stationery (and time is travelling at normal speeds), doesn't a stationery observer outside the bubble with his ADVANCED sensor see it as travelling at the speed of light from point A to B? Your spaceship and the immediate surrounding space would not violate Einstein's theory because it is stationary. The bubble doesn't have any mass because it is a field. No current theories are violated.

But oops, I guess this thread is about FTL travel based only on current theories and other future possibilities are not relevant. But double oops, trying to achieve maybe HALF FTL speeds are also future possibilities...... If we can't even achieve those speeds AND observe it, it is also irrelevant to discuss about time dilatation and time paradox and what not, no?

Ok ok. This thread is about travelling near or at speed of light based on current theories/propulsion technology which SAYS that it can't be done and other theories/future possibilities are irrelevant. I understand.

This post has been edited by kmarc: Dec 22 2009, 07:33 AM

As to your question, I'm not able to provide an answer - haven't done GR yet [it depends whether the axioms of SR do generalise naturally into GR - from this first look at this metric, it doesn't seem to]

It is also possible that I am your mother/father/grandfather. Have you considered that possibility yet? Or that everything that happens in the universe is actually due to fairies. Or that angels move objects in such a mathematical manner as to be able to be described by our current theories, and they might choose to change it anytime to 'suit' any other theory available.

What I'm trying to get at you is that, sure, anything's possible, but most 'possibilities', when tested, are shown not to occur. It was once thought that atoms were knots in the ether, but that was shown to be wrong. Let your imagination flourish, but I'd advise you not to think that possibility means inevitability, which is what you seem to be implying here. Not all science fiction will turn out to be true.

Or to use your example: Everyone thought the Earth was flat, and then they found it was a sphere. Well, why couldn't it be hyperbolic? Why couldn't it be a Klein bottle? Why couldn't it be a torus? Why couldn't it be various other shapes? - they're all possibilities. Sure, speculate all you want by assuming it's some possibility x, but it is not inevitable that your assumption is correct. But yes, if you indeed want to discuss time travel, and have to assume one of that, go ahead, but always be aware that it depends heavily on the assumption, which may turn out to be false after all

Now, what theory do you propose then, that has physical basis in our universe? (note: GR describes a set of universes, that certain solutions exist with interesting properties, e.g. wormholes, doesn't imply they exist in our universe) That's the big thing distinguishing science from science fiction, which seems to just take a problem, and proposes a miracle solution, and builds something upon it. Fair enough if they want to make stories out of it. But these miraculous solutions may turn out to be completely untrue, which is a more general point I'm trying to make here, and which is why I've been posting in this bloody thread so much

Yes, in a sense I'm saying they're irrelevant, because the existence of such a theory hasn't been shown yet, and even if it exists, FTL (we're making the assumption here that FTL means time travel - this might not be true either) might never be possible in all these theories, which is the point I'm trying to get at here really, and there are reasons for that, for one, causality, and wrecks the idea of entropy, mass-energy conservation, etc, etc... (again, assuming FTL does mean time travel, backwards). Sure these concepts might end up being replaced in the end, but the strength of a new scientific theory is that it is able to explain all previous phenomena explained by the scientific theory it succeeds, and be able to describe something new that the previous theory wasn't able to, i.e. it would still have to explain how those concepts I put up above still 'work' within its new framework.

This post has been edited by bgeh: Dec 22 2009, 10:05 AM

What u guys england2 ah?

shhhh... orang tua2 nak berborak.

dok tepi.

I think you have confused the points of information moving at the speed of light with things physically moving at the speed of light. When we see things, we see them as they are when light has left their surface. That absolutely doesn't equate with things moving at the speed of light. That's like saying when you hear your friend's voice as he shouts to you from the opposite building, it means he's traveling at the speed of sound!

Taking your example, when we see a car moving faster than us, we know he's faster because of his relative speed. If we measure his speed to be 20km/h faster than us, it could mean he's accelerated 20km/h ahead of us or we have just hit the brakes and slowed by 20km/h with respect to the car next to us. If we measure based on a fixed frame of reference, then we'll know for sure who's speeding up and who's slowing down. That's one of the basic points of relativity.

We do these measurements based on visual observations, or lasers, or radio waves, because EM waves are the fastest things we can use. So we compare our speeds based on the traffic light behind us. The sight of the lights arrive to us at the speed of light. We're using 'c' as the scale for our ruler.

When we travel at the speed of light, time doesn't move backwards. Time stops. Mathematically speaking. Time "stops" because when we move at the speed of light, what do see at our reference point? We'll be seeing the same image, because successive images can't catch up with us. We're moving at the same speed as that bit of information (that's traveling at 'c') that we're using as a ruler to measure our time and speed. For example, if we move at 'c' away from a stopwatch, can we see the stopwatch counting up? We'll only see the same signal that left the clock the instance we hit the speed of light, because the subsequent signals can't reach us. Hence, we see the stopwatch "frozen", and time has "stopped". But, the clock on our ship will continue running! Time is running on the moving frame, but time appears to have stopped outside of the moving frame.

Now, if we move faster than light (if we could), what would happen? We would be outrunning the signals from the external clock. We'll start to pick up the signals that had left earlier. We'll see the numbers that came out earlier, and it would look like the clock is reversing, because we're outrunning the speed of the information transmission. BUT, the clock on our ship will still be running forward, and we're still measuring time!

Outside of our reference frame, nothing has changed. If we were to stop our engines, we won't be in the past, we'll still be in the present/future (i.e. a few hours after the flight started) because, we didn't gain any time. As we slow down, the signals start to reach us again. At first, compressed. And then, it'll space out again in 'normal' time i.e. the one-second ticks match up to the rate of the clock on the rocket ship. It'll be compressed because of the wavelength shift of crossing between superluminal back to subluminal speeds. More likely than not, the information in between is missing and we'll just see the jump of a few missing seconds.

So, whether we're moving close to the speed of light, at the speed of light or faster than the speed of light, we're ageing normally within our ship. It's just that time looks different when we compare it with the external reference frame.

---

Added on December 22, 2009, 2:38 pmWhen moving close to the speed of light, we see objects "squashed" mainly not because they have physically shortened, but because the light from that object has blue shifted. Not only would it look shorter (because the wavelength has compressed), its colour will also shift towards the blue end of the spectrum. This shortening or lorentz contraction is mathematically calculated based on the difference between your velocity and the speed of light, based on how light waves reaching a relativistic observer would compress.

Some would say that you'll physically compress as well, which is a logical extension of the fact that the fundamental forces holding atoms together propagate at the speed of light, so when we're going relativistic, these forces get blue-shifted and atomic structures get contracted physically.

This post has been edited by jswong: Dec 22 2009, 02:38 PM

WOW. Great explanation. That's what I been thinking (if the statement is right).

Errrmmmm.... I read your reply 5x and I'm getting a headache....

The only part I understand/agree with is the bolded part. Could you summarize the rest?

Just to reply some of you questions/statement in short:
1) When and where did I state that possibility means inevitability and all science fiction will turn out to be true? Where?
2) The Earth is round because it is proven to be round. Why speculate further as to the possibilities of the shape of Earth when it is already been proven? It is like saying "2+2=4" but maybe it could be 5... or 6.... or -1.....
3) I did not propose any theories. What I'm saying is that researchers have BARELY scratched the surface of the universe and there will be new discoveries and theories. If we only confine ourselves to available theories, then we will not progress. I did mention that current theories might be improved upon or disproved by other future theories.

This post has been edited by kmarc: Dec 22 2009, 07:20 PM

On the twin paradox subject, many forumer suggested that both the twin should aged the same when B touch down on earth as aging is a biological process and both of them should experiencing the similar molecules changes regardless of the velocity and other factor differences. Both should aged 40 years old and not one (A) 40 years and (B) 28 years.

Just like you, it also feel strange when I first tried to understand the special theory (SR) and general theory (GR) of relativity. Both theories defy the common sense we known for years and tells us a different phenomenons on how we perceive things.

The theories indeed suggests that B, the traveler aged slower (hence, younger) than A on earth due to the following:

1) The blue/red shift (like doppler effect) of light on both of the reference frames
2) Time dilation factor - The faster the speed closer to c, the higher the effect
3) Acceleration effect experienced by B in the ship while A was stationary on earth
4) The effect of gravity. Gravity has confirmed slowing down the time. When B is in a ship, the acceleration/deceleration effect on him was like a large impact of gravitational forces acted on him
5) Space/Time compression factor

An experiment was actually been done which was to start off with two identical, synchronised atomic clocks, keep one on the ground and fly the other one around in a plane for a while. When the plane lands, the clock that was in the plane is found to have run a little slower than the one on the ground.

Still not convince enough, ask this question, what do you mean by both A and B should be aged the same, ie the grow rate are the same?

The word rate means that it is time dependent. When traveling near light speed, time is no longer like what we perceive at low speed. The near light speed experience alter the space time continuum. One needs to throw away the idea there is only one "absolute" time idea in order to appreciate this.

If you are interested to know more, here is one of the link:

http://www.gmarts.org/index.php?go=420

Summary
Bob and the rocket have aged only 12 years while Ann and the Earth have aged 20 years.

The twins' times are different when Bob returns because Ann has seen Bob's time running slower than her own on average, while Bob in the rocket has seen Earth time running faster than his own on average.

Cheers.

Twins paradox and time dilations are very real phenomena. The most common example given is GPS. GPS satellites take time dilation into account (and also the slower passage of time in weaker gravity compared to the surface of the Earth). If the satellites do not do this, their time-keeping (and hence distance measurements) will be all wrong. The fact that our GPS units can reliably show us our locations to within a few feet of accuracy proves that time dilation is correct!

I used the word imply. There was no explicit mention of it, hence the word imply. You're implying that future theories will allow such a thing, and this is quite clear, to me at least, reading your posts above. I'm saying that future theories may or may not come out to replace the existing ones does not imply that FTL will ever be possible, whereas you seem to be implying that because we know so little, FTL is possible. It is not known whether it's possible, which is what I'm trying to get at.

I used the Earth is round analogy because you seem to have wanted to show that future theories might change the way we see things, which is true, but I wanted to point out that it could've been any other possibility - it wasn't inevitable that it was going to be a sphere, and putting it into the context of the discussion above, you've neglected the possibility that FTL is impossible in our universe, since you're constantly pushing the 'FTL may be impossible in current theories, but who knows if it's possible in some future theory?' aspect. It may end up to always being impossible.

I'm not saying you should confine yourself to available theories, but what about my fairy/angels theory? I understand that you're inspired by science fiction, and it would indeed be nice to have it come true, it may end up being impossible in the end after all, which is the thing I'm trying to bring into the discussion. Sure, imagine away, but do realise that it may end up impossible in the end, because from what I'm reading of your posts, you seem to only consider/bring up that possibility in future theories without mention that it need not appear in any future theories.

And yes, this wasn't specifically tailored at you alone, which is why you won't recognise some of the things I mentioned above. Rather, this is a general critique about what I've seen in this forum from plenty of participants who love talking about things that are taken for granted in science fiction, e.g. very fast travel between stars, and dreaming up miraculous solutions to problems, and they talk as though it is an inevitability - but they're assuming such a solution exists, when that hasn't even been shown yet.

This post has been edited by bgeh: Dec 23 2009, 11:49 PM

Does this mean that if we travel at the speed of light, we will biologically age much slower? Would we return back the earth (frame of reference) and see our twin as a grandfather while we are still young?

Imagine an ant on a flat surface. As it crawl on the surface, that is the absolute speed of the ant on the flat surface. Time, is like the 3rd dimension to the flat surface. When we say speed of light appear constant to all observer, disregard if the observer is moving or stationary; it's like saying an ant observing a ray of light shining in the 3rd dimension across the flat surface.

Light, in the 3rd dimension, will always appear constant to the ant, be it that the ants are moving or not. However, if the ant is moving at near LS, by normal physic, the speed of light in the 3rd dimension should have change.

When relativity theory say that light will always be constant, the last statement is not possible (where light speed have change). Rather than the light speed is changed, time slowed down.

In our 3 dimensional world, light pass through our 3-D world, slicing through the time-dimension. Which is why light speed will always be constant relative to us, no matter where and how fast we travel.

As we travel faster, still within our 3-D world, we need to obey the "light speed is constant". If not we will catch up with light speed (aka the scenario describe by jswong). The only way for light speed to remain constant, is to slow down the time around the traveler. At least that is how I reason it.

The ultimate question is, does the traveler action automatically slow down as well too? Or his action is still at normal speed but only the time slow down?

If the answer to the first one is true, then he will observe that light is travelling faster than lightspeed. If the answer to the second question is true, then he would probably aged the same as his twins on earth.

no. we dont biologically age slower. we experience everything at normal speed.

assume we travel near lightspeed for 1 year. in our experience (the traveller), only 1 year has passed. but due to the time dilation effect, people on earth probably have experienced 20 years. it's probably like watching the earth on fast forward from outside. and for the earthlings, it's probably like watching the travelers in slow motion.

but like we've discussed before, ur biological clock wont be extended. u will still die by the age of 80-90.

Thx for not getting upset or angry. Some forumers would just become irritated and angry when I "throw" a spanner in their well-oiled machine (aka belief).

"Imply" is such a strong word in this context. I would say "hope" would be a better word (which I did include in brackets early on in the discussion).

For the sake of argument, let's just assume that in this universe, for eternity, FTL is totally and absolutely impossible. That is to say, any object with mass in it's original unaltered state can never travel at FTL speeds. Fine.

However, I'd like to think that in the future, there would be a workaround to this problem. That's why I mentioned something like the warp bubble/field as an example, that doesn't violate any theories but work around it. If we humans are "condemned" to travel at sublight speeds, then we would probably be confined to this region of space for all eternity, however advanced we are (assuming we don't blow ourselves up first!!!). For advancement of the human race, that's a scary thought.

Here's what I'm getting at (Lot's of googling for this). The universe as we know it is estimated to be 93 billion light years across. There are an estimated 100 billion galaxies with each galaxy containing from 10 million to one trillion stars. Our Milky way galaxy (one out of billions of galaxy) is 100,000 light years across and contain 200 billion stars. Our sun is only one star among billions in our galaxy and the nearest star system is Alpha Centauri (wooo! I like the movie "Lost in Space"!!) which is about 4 light years away. The number of stars in this universe would be so much that only a googolplex can encompass it.

Most people would say our human mind probably could NEVER EVER comprehend the scale and numbers involved. That's why it always humbles (and inspires!) me to see this picture from the Hubble space telescope (compressed because it is too large):



The picture was taken from a region of space indicated by the red square below the moon. Each blotch is not a star but a galaxy! You can download the full big picture by googling or here: http://upload.wikimedia.org/wikipedia/en/e...eComparison.jpg

Furthermore, our time in this universe is not even as long as "a blink of the eye" as compared to the estimated age of the universe (estimated to be 13.7 billion years). As such, we are just a tiny tiny tiny tiny miniscule micro insignificant speck in this universe.

This is where I'm coming from. To think that current theories are "correct" and "ultimate" is incorrect, to put it mildly. We have just barely scratched the surface to the secrets of the universe. There are and will be lots of new discoveries to be made, new theories to put forward and new technology to create. With this in mind, some might even dare to say that it is not "IF' we can FTL, it is "WHEN". Again, assuming that we don't blow ourselves up with our own technology in the future.

An approximate analogy to this is that we are a bird. With our bird brain (haha ), we are happily chirping around, flying here and there looking for worms, build a nest and find a partner, die happily seeing our chicks grow up and fly away. In our "bird" world on the tree top, we only understand our own world as we see it while we can't comprehend the world around us. We scold with vigorous chirping when a loud plane passes by. We look on with curiousity at the multitude of cars below and we think humans are aliens coming to grab our eggs. We do not understand words or alphabets or mathematics or science. Yes, we can see and observe all those things around us but just do not comprehend what they mean.

My only regret is that our human lives are short, that we will pass through this period of time as an insignificant being that nobody will notice while the universe goes on without a hint of our passing.

Lastly, you may say that since we are in this age with our limited current theories and technology, we just have to make do with them. Fine by me. As I have stated earlier, I have no quarrels with current theories and what they implicate.

Ok, I'm blabbering . Hope you get what I mean.

Note : Sorry that I'm off-topic. My last blabbering post, honest!!!

This post has been edited by kmarc: Dec 24 2009, 01:07 PM

in reality, the human mind cannot really comprehend numbers that are larger than ~100. so yeah, the billions of stars i nthe billions of galaxies is really incomprehensible to the typical human mind. along with millions and billions of years

when those numbers are thrown around, the general idea is "a lot"