Celestia Forums

Is there any way or add-on I can apply that when Travel is applied at near-light (c) velocities, the scene is crunched appropriately and time is dialated -- though obviously since the sim isn't likely tracking star motions and anything slower than pluto I guess the coolness of time dialation making all things seem -- what was it now, slower in the rear view mirror (or at least the outskirts of my vision) and faster in the foreground? Also, using Relativity, although light view at FTL is somewhat whimsical at best, could the effects be applied in from a tacheon-eyed view assuming we could still interect in SOME way with light? At c, all is a seathing Exawatt pulse of EM straight in front of you -- poof, you infinite-mass bugger, you dead by the most deadly raygun immaginable. But apart from the world looking very boring at c, could we at least view it around c, certainly slower, maybe faster?

n/t

TimeHorse wrote:....
Also, using Relativity, although light view at FTL is somewhat whimsical at best, could the effects be applied in from a tacheon-eyed view assuming we could still interect in SOME way with light? At c, all is a seathing Exawatt pulse of EM straight in front of you -- poof, you infinite-mass bugger, you dead by the most deadly raygun immaginable. But apart from the world looking very boring at c, could we at least view it around c, certainly slower, maybe faster?

Man,
this is wild;-)

Do you think you understand what you are writing here?

You better recall that --while tachionic matter might well exist -- we immediately would run into a /violation of causality/ once tachionic matter (v>c) is able to interact with normal, non-tachionic stuff (v<c)...

A violation of causality -- in popular terms-- would e.g. mean that you can kiss your girl-friend before touching her

Bye Fridger

Fridger,

Now that you've ruined our hopes of ever reaching the stars, do you realise that you've just put an end to the lucrative SciFi business?

Bad, bad boy, you should be ashamed of yourself!

Christophe wrote:Fridger,

Now that you've ruined our hopes of ever reaching the stars, do you realise that you've just put an end to the lucrative SciFi business?

Bad, bad boy, you should be ashamed of yourself!

Why, Christophe?

all that is needed is a little more patience and a good "deep freezer" aboard

Perhaps some clever SciFi 'business managers' also stumble over a lonely wormhole one day or a hidden door to take a "shortcut" via extra dimensions....

These possibilities are at least not immediately ruled out.

Bye Fridger

Wow this all sounds interesting, is there a place where I can read more on tachionic matter and violation of casualty?

Scorpiove wrote:Wow this all sounds interesting, is there a place where I can read more on tachionic matter and violation of casualty?

Hmmm... a good explanation of why FTL causes causality violations can be found here.

I mean if I can understand it, anybody should be able to

chaos syndrome wrote:

Scorpiove wrote:Wow this all sounds interesting, is there a place where I can read more on tachionic matter and violation of casualty?

Hmmm... a good explanation of why FTL causes causality violations can be found here.

I mean if I can understand it, anybody should be able to

Thanks I appreciate it.

t00fri wrote:all that is needed is a little more patience and a good "deep freezer" aboard :lol:

As long as you don't fear psychotic computers, you're ok I guess.

t00fri wrote:Perhaps some clever SciFi 'business managers' also stumble over a lonely wormhole one day or a hidden door to take a "shortcut" via extra dimensions....

These possibilities are at least not immediately ruled out.

I think we might as well bet on our current understanding of the world being totally wrong. You won't make me enter a worm-hole anytime soon.

Okay, going back over the Lorentz contractions, I would suggest the following in terms ONLY of spacial orientation. I may cover blue/red shift in another post but as hinted at, the faster you go, the shorter the wave lengths become and at c its worse than GoogleWatt Gamma rays.

From a radial point of view, at speeds near c, there is a length-dialaton equivalent to lambda = sqrt(1-v**2/c**2). So at v = 3/4 c, you have a lambda of 1/2. Thus, objects that would normally appear 100 lyr appart will seem a mere 50 ly appart. This should also apply to items in front of you, causing them to appear "closer". The net effect is a tunnel effect that allows you to see your rear on your periferee receeding away at an appropriate shift. If you look back at 3/4 c, you will probably see pitch black because all the light coming from behind you is now IICC directly overhead, to your left, to your right, below and all other cardnal angles in between.

What interests me is that in Celestia, traveling even at c, never mind 3/4 c -- like real life -- can be quite boring, even when one takes time dialation into account. So often 1 lyr / s is a more appropriate speed for travel. Unfortunately, as you can see lambda becomes immaginary at these speeds. So how do we display anything whose relative distance is imaginary?

I suggest for the purposes of symmetry that we take the absolute value of the resultant lambda to get the reverse effect. Or, alternatively, we assume all physics is imaginary and simply multiple all terms by i, getting negative the absolute value in most cases.

Thus at 5/4 c, you again have lambda = +/- 1/2 and therefore the same effect as 3/4 c. At 2 c, you have the universeal view equivalent to rest, because lambda = +/- 1. At 1 lyr / s, you have the most percular effect of your entire view being concentrated behind you because lenghts have been expanded so greatly.

What do you think?

If relativistic effects ever get incorporated into Celestia, I'd expect time dilation to be part of it. In other words, the observer's point of view would see the universe as shrunken and traversable in a small amount of time.

selden wrote:If relativistic effects ever get incorporated into Celestia, I'd expect time dilation to be part of it. In other words, the observer's point of view would see the universe as shrunken and traversable in a small amount of time.

True.

Relativistic effects doesn't do any harms to SciFi, on the contrary.

Here's why (sorry for my bad English, I'm doing my best here) :

in classical physics, when you want to travel to the next star from our Sun (about four light years from the sun), you could do it with ANY speed you want. There's no speed limit. So you can reach the star in, say, 1 minute only by traveling with a much faster than light velocity. When you return to the Earth, 1 minute later, people on Earth will have experienced only 2 minutes of life. Time is absolute in classical physics and runs the same for everyone.

In relativistic physics, you can't travel faster than light. Time is relative and doesn't run the same for every observers. And there is a relativistic contraction of lenghts and distances. So, if you want to go to the next star, you can do it ALSO in one minute only (in your own spaceship), because the distance appears to be contracted if you travel at, say, almost the speed of light. But there's a price to pay. When you return to Earth (one minute later, in your spaceship), people on Earth will have experienced a very long time of life, much longer than you. Earth is now the Planet of the Apes. This is the well known "twin paradox" of relativity theory. There's no paradox here, in reality.

So you see, relativity isn't in conflict with sci-fi, it supports it, actually.

TimeHorse wrote:...
What do you think?

The present approach in Celestia is as follows as I have detailed many times before:

The observer is treated as a "testbody", as we generically would call it in theoretical physics:

-- no mass hence no sensitivity to gravity
-- able to travel with infinite speed >>c, i.e. not subject to relativistic effects.

Such theoretical "constructs" are a familiar concept and used frequently in various contexts.

They are merely meant to /probe/ a system where physical laws are realized consistently, without interacting with it themselves!

[ Often one rather considers "testbodies" that are supposed to be infinitely heavy such that they would not experience any recoils from the system they are probing....]

With the role of the "Celestia observer" made clear,
let me recall that I have implemented in Celestia the simplest "relativistic" effects due to the finite speed of light a long time ago in form of the light travel delay option.

Clearly further options can be implemented but things get quite non-trivial easily. Such options mostly would refer to treating the observer as a more or less real spaceship:

-- associating a finite mass to that "spaceship" is problematic, since a physically correct simulation becomes far too complicated (and time consuming) very easily. We have discussed this often and agree that we leave feasible naive i.e incorrect implementations of such gravity effects to game programmers in respective software applications...

[ Celestia does implement interplanetary gravity effects, however, in a very sophisticated manner in form of the VSOP87 theory involving 100's of correction terms ...]

-- for our massless realistic "spaceship" we could correctly implement special relativity by optionally restricting its speed exactly to the speed of light, as appropriate for a massless "body".

This would allow us to correctly incorporate the relativistic spectral Doppler shifts, the modifications of the field of view and time dilatation effects.

Hopefully, we get to this in a future version of Celestia.

Gravitational lensing:
--------------------------

This would be a most interesting effect due to general relativity that could be correctly realized, once we would get off to work on a "Cosmological Celestia mode".

I have tried repeatedly to get us into that exciting extension, but so far failed apparently due to a massive "inertia" of the other developers...Perhaps towards Celestia 2.0 something will happen in that respect?

Bye Fridger

t00fri wrote:

TimeHorse wrote:...
What do you think?

The present approach in Celestia is as follows as I have detailed many times before:

The observer is treated as a "testbody", as we generically would call it in theoretical physics:

-- no mass hence no sensitivity to gravity
-- able to travel with infinite speed >>c, i.e. not subject to relativistic effects.

Bye Fridger

Even massless particles are following "lightlike" (or "null") geodesics of spacetime, and are sensible to gravity.

Even a "testbody" cannot travel faster than light in (special or general) relativity, or it isn't a "test" particle.

Your Celestia observer is a ghost. Or maybe a virtual particle ?

Personnaly, I see this in a more complicated way, which could be consistent with relativity theory :

There's an infinite set (or collection) of STATIONNARY observers, everywhere in the Celestia universe (which is Euclidian, by the way). All those observers are using synchronised clocks and defines a single reference system. When the camera is moving, we actually gather the information from those observers all the way and make a "movie". There is no need whatsoever for relativistic effects here. The camera isn't really "moving".

So no Doppler effects, no time dilatation or lenght contractions of space. The camera is just a way to jump from one stationnary observer to the next one.

Cham wrote:

t00fri wrote:

TimeHorse wrote:...
What do you think?

The present approach in Celestia is as follows as I have detailed many times before:

The observer is treated as a "testbody", as we generically would call it in theoretical physics:

-- no mass hence no sensitivity to gravity
-- able to travel with infinite speed >>c, i.e. not subject to relativistic effects.

Bye Fridger

Cham,

cham wrote:
Even massless particles are following "lightlike" (or "null") geodesics of spacetime, and are sensible to gravity.

Yes, but only in /general/ relativity. That only becomes relevant in practice on cosmological scales like in case of "gravitational lensing". Within our solar system, for example, these effects are certainly negligible. I hope you agree...

Cham wrote:Even a "testbody" cannot travel faster than light in (special or general) relativity, or it isn't a "test" particle.

The observer of course would have to take "non-causal Euclidean shortcuts". Why not?;-)...Causality for a "testbody" does not seem to be essential, really...

Cham wrote:Your Celestia observer is a ghost. Or maybe a virtual particle ?

Sort of...

Cham wrote:Personnaly, I see this in a more complicated way, which could be consistent with relativity theory :

There's an infinite set (or collection) of STATIONNARY observers, everywhere in the Celestia universe (which is Euclidian, by the way). All those observers are using synchronised clocks and defines a single reference system. When the camera is moving, we actually gather the information from those observers all the way and make a "movie". There is no need whatsoever for relativistic effects here. The camera isn't really "moving".

So no Doppler effects, no time dilatation or lenght contractions of space. The camera is just a way to jump from one stationnary observer to the next one.

Yes, I tend to agree. You may formulate it this way. If you prefer.

Bye Fridger

Well, if tachyons are more than theoretical than wow. Since time stops at the speed of light i would imagine it would speed up again when its past by and object of negatiive mass (im supposing the tachyon is a particle of negative mass?). However time would travel backwards in this case, would it not?


Second Comment: If at light speed time is stationary and past, present, and furture are one, does that mean in a sense that everything has happened already. Which brings me to another theory of mine. Time must be infinite for their to be light, right? Maybe this is just a crazy connection.

this is interiesting does anyone have a comment on what chrisr said?!

Cham's response is quite correct and gets to the nub of the matter.

In Celestia when it says 'Speed=c', this is the classical Newtonian c. However, to achieve the same effective speed in relativity, you simply apply the transformation of distance/time *but using the space traveller's measurements of these* and not the earthbound observer's.

This turns out to be c/sqrt(2) = 71% c.

So if Celestia simply converted its Newtownian velocity to a relativistic one (a simple calculation), you would see how fast fractions of c really look. Of course, you can't go past c, *but you don't need to*. As Cham points out, you can get anywhere in the universe in any amount of time (theoretically, of course - but that's what we're about). In the real world, you need to accelerate pretty hard to get to Alpha Centauri in a day, but there's nothing stopping you from doing it, in theory.

When you see speeds of 1ly/sec in Celestia, this should be converted to a relativitic one and it would come out to, say, 99.999% c.

So let's assume the programmers can add that conversion in to display your speed in rel units (trivial) and we have at least an accurate depiction of the time you get to places.

Then what can be added (over time) are the following:

Set tau (time at origin) to use dilation so that your system clock speeds up as you slow down near your destination and you then show your 'home time'. E.g., you zip off to Jupiter at high speed on 20040101. You get there in three days and slow down and stop. Your system clock no longer reads 20040104 but rather 20040120 or whatever the value for the dilation is (I'm too lazy to calculate that now, but again it's straightforward).

Then we have
1) correct speed as a fraction of C
2) the real time (home time)

Both these calculations only need to be done once per iteration (unless you want to be extremely accurate for bodies moving relative to each other, but this is overkill) so it shouldn't chew up any CPU resources.

After this you can look at incorporating some of the visual relativistic effects like headlighting and doppler shift. These have to be done per object, because the effects depend upon the projection of their distance in the direction of travel. Perhaps these will then become resource intensive. Still, if they're optional, then why not!

I hope the authors think about this because I think it would be such a brilliant educational addition to highlight the key message of relativity: time really is linked to space! If a user travels through the galaxy for half an hour at 99.9999999% c and returns home to find the sun has enlarged and gobbled up earth in the few billion years while you were out playing (even though it was only half an hour to the traveller), I think that will be a pretty powerful demonstration.

What do you all think?

Cheers
Sean

Sean,

one important ingredient into Celestia's design philosophy is to keep its physics content conceptionally transparent.

The implementation of (special) relativity is on our "shopping list" since a long time. But there is no point to do it in this incomplete, hybrid way as you suggest. Besides trivial relativistic kinematic effects on which you dwell above, we have to incorporate also a lot of less trivial new 3D graphics effects related to the relativistic distortions of the field of view along with various related phenomena.

So far I have only implemented the simple "light travel delay" option (LT) that is handy if you want to do precise timings of celestial events.

Bye Fridger

chrisr wrote:...
Since time stops at the speed of light i would imagine it would speed up again when its past by and object of negatiive mass (im supposing the tachyon is a particle of negative mass?).

...

No, tachyons have negative mass squared, i.e. imaginary mass! Negative mass is physically indistinguishable from positive mass, i.e. that sign is not measurable. It's taken positive by convention in particle physics.

Bye Fridger