119 réponses à ce sujet

[Kurt M.]

superimposed wrote...

Gladiador2 wrote...

Rodriguer2000 wrote...

 seems crazy but its the only way i see us traveling to distant planets lol real life mass relays

Humanity will rot in Earth. Period.

We even lack the technology to regurarly travel thought our own solar system (and it doesn't matter anyway, as there aren't garden worlds here apart from the Earth). We'll never have the tech required to travel around our nebula for sure, and much less to travel around the Milky Way. At most we could colonize the Moon, Mars, and a few Jupiter moons, and the latter option is already extremely improbable. Again, it doesn't matter, because nearly all the resources would need to come from Earth anyway.

I've the theory that maybe if religions wouldn't have existed (they've been a BIG slowdown in science), and humanity wouldn't have been so stupidly selfish, then maybe by now we'd have at least regular travel thought our solar system, a few viable colonies, and Helium-3 engines. And with such a good base, we would still be in trouble.

The only *REALISTIC* chance we have is that any other sapient species find us and teach us how to space-travel, much like the hanar did to the drells. If not, we'll end like them. And it's highly improbable, too

It took us over 200 years since the Industrial Revolution to get a manned Rocket to the Moon. It took us only forty years after that to make a manned Rocket to Mars Plausible. Technology grows at an exponentially increasing rate.

Maybe. But Earth's degradation, too. And I bet the latter is faster than the former.

And anyway, progress is still too slow. Closest star from here is nearly 5 light-years, and there's no guarantee it has a system with any garden world.

[TheUnusualSuspect]

max_ai wrote...

TheUnusualSuspect wrote...

adam_grif wrote...

Two spaceships, A and B are moving apart from each other at 0.866 times the speed of light. This is chosen for convenience' sake. It reults in a time dilation factor of two, which means that the from A's perspective, B's clock is ticking at half speed and vice versa.

Ok, this is where I get a little fuzzy about it.  Are both ships travelling at 0.866c away from the same relative start point in opposite directions?  If so, isn't the time dilation equal for both, and therefore wouldn't they both observe their clocks to tick at the same speed?  If not, why?  I got to Advanced Physics in Uni at 2nd year, but this stuff did my head in and I dropped it, and admit to never fully grasping relativity properly, so please bear with the fool and entertain my silly questions.

Since the ships move in constant speed then they'll observe their clocks just as you'd observe your own clock, but if ship A wants to measure the clock of ship B (or its location) then relative effects come in.
A measures the speed of B to be roughly 0.99c

Anywho special relativity isn't very helpful for such scenarios (if they were to happen), because ships tend accelerate, and special relativity doesn't take that into account. You need to account for red shift and stuff (who's red-shifting, who's not), basically it's general relativity already, which is by far more complicated.

Okay, I think I got that, but I'm still not convinced that this causes the paradox that adam_griff describes.  Maybe I'm getting confused by the frames of reference thing?

If both ships are affected by time dilation equally, then wouldn't both ships fire at the same time (from the perspective of an observer standing at the start point), irrespective of A thinking that B fired at 4 secs on B's clock.  A's clock says that 8 secs is up, and that's going to happen at exactly the same time as B's clock saying that 8 secs is up.  Wouldn't the observer standing in the middle just see both ships firing after 16 secs has passed for him?  Would that be true?  That doesn't seem to create a paradox to me (viewed from the perspective of the observer).   I mean, it doesn't matter that A perceives that only 4 secs has passed for B, the fact is that 8 secs have still passed for B by B's on-board clock. 

Alternately, take the scenario of if the observer has a gun, and a ship flies away from him at 0.866c, the ship has a time dilation factor of 2 relative to the observer, then the observer fires his gun at 8 secs passed.  The ship registers the impact at 4 secs passed on the ship's clock, and fires back.  The return shot still hits the observer at some time after 8 secs according to the observer, so there's still no paradox.  According to the ship though, even though the shot is instantanous, the light-signal from the bullet hitting the observer won't reach the ship until after 8 seconds has passed on the ship's clock, so there's still no paradox.  Doesn't matter if the observer is standing still, or travelling at speed, there's still no paradox.

Or have I missed some critical point of the example?

Modifié par TheUnusualSuspect, 28 février 2010 - 12:43 .

[SnakieHelah]

Hmmm, to the one who said that aliens would give us some kind of tech,

That is naive to think, especially for us humans, I mean if aliens would be smart enough to make spaceships, they would be smart enough to watch our progress and give us when the time comes, but the thing is, the time will never come, Do you even imagine what would happen if Earth's government would find out that there ARE aliens anywhere near us? Remember that what happened in mass effect's story, they gave tech to the Krogan, they weren't even in their civilazation stage, and look what happened to them.

[adam_grif]

Hellhawx wrote...

With the exception of futuristic technology in Mass Effect. The game is holds true to what is realistic. The only unrealistic item is Eezo, its effect and cause of Mass Effect fields, which all surrounds Dark Energy.

In addition to Eezo, which violates conservation of energy and momentum, mass effect fields have the bizzarre additional characteristic of increasing the subjective speed of light when a mass lowering field is applied (inexplicably, there's no reason it would actually do that just from lowering mass). Inertial dampeners are also mentioned by Chakwas.

Then there's the Asari EMBRACE ETERNITY psionic silliness. The Reapers building ships out of gooified people is heinously unrealistic, because apparently they can only do it with specific species because they're triyng to abosrb their essence or some crap (aka Vitalism). The Reaper indoctrination is supposedly based around subliminal messages, which is pure pseudoscience and extensively debunked by science a looong time ago. Then there's the bizarre "brainwashing people makes them less competent" axiom, which has no real reason to be there other than plot convenience.

If we factor cutsccenes into it, all the space battles shown so far are massively silly. In ME1 everything just charged head on, threw slow moving fireballs around and flopped around at point blank like beached whales. Spacecraft (particularly the Normandy since we get the most time with it) act like atmospheric fighters, when they really shouldn't be. The whole occulus situation would have been trivially resolvable by rotation the Normandy without killing its momentum and then firing on them without engaging in a silly ultra-close-range dogfight.

Characters all speak fluent, unaccented English, which flawlessly matches their mouth movements (so it's not explained away by universal translators). Species can coexist, eat the same food and have sex with other species (except for the Quarrian/Turian thing) without worrying about foreign pathogens or anything.

It's no Star Trek, but Eezo is far from the only thing unrealistic in Mass Effect.

Dark Energy does exist in real life. It is being studied. Nothing is known about it except that it may exist in black holes. Will some sort of tech similar to Eezo ever be discovered, probably not a chance. Will we ever be able to travel Light Speed? Probably not. At least in Mass Effect, they keep science realistic even under the fiction of FTL travel (like red shift, etc.)

Dark Energy and Matter is the name given to "that thing that is causing galactic expansion to accelerate". It might wind up being someting as simple as us fudging up our understanding of gravity and there being nother there at all. Or it might be as some contemporary theories have it, a kidn of matter and energy that don't interact with any force but gravity, yet make up > 90% of the total energy in the universe (meaning <10% of matter/energy is the stuff we're used to).

[max_ai]

TheUnusualSuspect wrote...

Okay, I think I got that, but I'm still not convinced that this causes the paradox that adam_griff describes.  Maybe I'm getting confused by the frames of reference thing?

If both ships are affected by time dilation equally, then wouldn't both ships fire at the same time (from the perspective of an observer standing at the start point), irrespective of A thinking that B fired at 4 secs on B's clock.  A's clock says that 8 secs is up, and that's going to happen at exactly the same time as B's clock saying that 8 secs is up.  Wouldn't the observer standing in the middle just see both ships firing after 16 secs has passed for him?  Would that be true?  That doesn't seem to create a paradox to me (viewed from the perspective of the observer).   I mean, it doesn't matter that A perceives that only 4 secs has passed for B, the fact is that 8 secs have still passed for B by B's on-board clock. 

Alternately, take the scenario of if the observer has a gun, and a ship flies away from him at 0.866c, the ship has a time dilation factor of 2 relative to the observer, then the observer fires his gun at 8 secs passed.  The ship registers the impact at 4 secs passed on the ship's clock, and fires back.  The return shot still hits the observer at some time after 8 secs according to the observer, so there's still no paradox.  Doesn't matter if the observer is standing still, or travelling at speed, there's still no paradox.

Or have I missed some critical point of the example?

It seems like you have a mish-mash of clocks there.
When 8'secs pass on A's clock, according to A, B has different time (not 8 secs), and vice versa, and the observer has also a different time. That is all because they're moving at relativistic speeds relatively one to each other.
Moreover, the distances are not symmetric (they're only for the observer).
In any case, I already wrote you the first step in figuring out everything about this problem, now you just need to apply some Lorentz transformations and you'll get all the data you need (at what time each event occurs for each ship).
I haven't read the whole description of the problem up to the end because I'm too lazy at these hours 

[adam_grif]

TheUnusualSuspect wrote...

Okay, I think I got that, but I'm still not convinced that this causes the paradox that adam_griff describes.  Maybe I'm getting confused by the frames of reference thing?

If both ships are affected by time dilation equally, then wouldn't both ships fire at the same time (from the perspective of an observer standing at the start point), irrespective of A thinking that B fired at 4 secs on B's clock.  A's clock says that 8 secs is up, and that's going to happen at exactly the same time as B's clock saying that 8 secs is up.  Wouldn't the observer standing in the middle just see both ships firing after 16 secs has passed for him?  Would that be true?  That doesn't seem to create a paradox to me (viewed from the perspective of the observer).   I mean, it doesn't matter that A perceives that only 4 secs has passed for B, the fact is that 8 secs have still passed for B by B's on-board clock. 

Alternately, take the scenario of if the observer has a gun, and a ship flies away from him at 0.866c, the ship has a time dilation factor of 2 relative to the observer, then the observer fires his gun at 8 secs passed.  The ship registers the impact at 4 secs passed on the ship's clock, and fires back.  The return shot still hits the observer at some time after 8 secs according to the observer, so there's still no paradox.  Doesn't matter if the observer is standing still, or travelling at speed, there's still no paradox.

Or have I missed some critical point of the example?

The time dilation factor of 2 is between them. It's not that they both experience a time dilation factor of 2 when compared to people at rest, the two frames have a factor of 2 when you calculate events between them.

PS. I stuffed up before, the two parties are moving away from each other at a relative velocity of 0.866, as opposed to both going away from each other at 0.866 in their respective directions. Otherwise the time dilation factor is much larger than 2.

Relativity also means that 0.866 relative to each other is the same as one stationary object and one going at 0.866 C. This is why each party sees the other as ticking at half speed. From each's perspective, they are both correct. This seems odd, but the whole point is that there is no such thing as the univeral "now".

As for what it all looks like to a third party observer, this is the diagram whipped up by somebody smarter than me:



And some text:

The paths O1 and O2 take through spacetime are the colorcoded arrowed
lines. The events in spacetime that each considers "simultaneous" and
"8 seconds after the start" are along the thinner, non-arrowed
colorcoded lines. So we see that, each of the three observers thinks
the other two have slow clocks, and that if we are allowed to move
faster than a lightcone, we'll end up going "pastward" in somebody's
reckoning.

We can trace out the shots on this diagram, also.
Step through it one more time: if green shoots
at 8 seconds out, the shot will go along the green "line of simultaneity",
and hit blue at 4 seconds elapsed. If blue returns fire from there,
it will return along a line paralel to the blue "line of simultaneity",
and catch green napping at 2 seconds elapsed.

You can see more about spacetime diagrams, and more about the
notion of "lines of simultaneity" at

sr-ticks-n-bricks.html
sr-twin-01.html

Finally, FTL still can can bite you in non-instantaneous cases;
where we're only going a "little bit" faster than light.

If you warp out, go to Tau Ceti, then with normal reaction engines
accelerate away from earth, warp out again to go back to earth,
you will indeed get back before you left. (Presuming that the
real-space delta-v before the warp/hyperdrive/tachyon-watziz
trips was "large enough"... there are formulas for such things
in the textbooks).

Modifié par adam_grif, 28 février 2010 - 12:52 .

[Lord Abrasion]

Lord_Moose wrote...

In the future we may very well find ways of traveling at ludicrous speeds to get from one star to another in no time at all.
Or we find a stargate in eqypt or a mass relay orbiting pluto, You Can Never Tell.
If you want to work on the mindcrushing math it would take to calculate the perimeters to do such a thing be my guest.

We already know how to do that... in theory.

[Biotic_Warlock]

Well seeing that no-one has found a prothen beacon (yet *shifty eyes*) tahtis ulikely. Would be cool if we could have some.

[wolf99000]

I know that they think wrapping space might work but we are way off being able to do it



just found this



An FTL propulsion system — based on Alcubierre’s warp drive — that utilizes dark energy to propel a spacecraft faster than light has been proposed, and could revolutionize space travel



just found it interesting with all the dark energy talk in me 2

[Vaenier]

screw mass effect fields, I say we use Hyperdrive and Stargates.

[Marilynn-22]

Warp Drive!

[TheUnusualSuspect]

Thanks for persisting adam_griff and max_ai, but please bear with me one last time.

The speed of light is not instantanous as we all know, so if B is observing the clock of A, it's really observing some event in A's past (time dilation), but not really A's "now". If B is 8 seconds away from A (according to B's clock), then by the time that B see's A's clock reach 4 seconds, light from A's clock had to travel 8 x 0.866c (or about 7 secs) to reach B. So by my reckoning, if B fired an instantaneous bullet that struck A at the time B reached 8 secs (viewed as 4 secs on the clock of A by observer , A would actually register that bullet hitting at 4 + 8 x 0.866s, or around 13 secs after departure by A's clock.

I must be getting it mixed up, but as you say, there's no concept of "now" aside from what we perceive as "now" in our own frame of reference, so surely by that tautology, what is "now" for us is not "now" for someone else, so how can firing an instantaneous bullet hit that other person at your local perception of "now"? We just defined that "now" is a local event, not a universal event.

I understand the 3 observers diagrame and the light cones, but even with that example, I still cannot rationalise that just because observer B perceives observer A as being at time 4 secs and fires an instanenous bullet that said bullet would actually hit A at A's clock time of 4 secs. B was looking at a historical event of A's clock, not A's clock within A's frame of reference.

There must be fairly basic premise here that I'm wrong with, because what I'm saying seems to make clear sense to me.

Thanks once again for persisting with this.

Modifié par TheUnusualSuspect, 01 mars 2010 - 12:27 .

[Knoll Argonar]

You people are just getting the topic too far.



I think it's simplier: unless we find another kind of radiation, or "dark energy" really exists and can be manipulated omehow like with mass effect fields, we're stuck in the "C = no mass" limit.



But it wouldn't be the first time science has changed it's paradigms. The Aristotelic-Ptolomeum universe system was even mathematically correct and "true", but that's just because they had incorrect rules.



I don't think modern physics are wrong at all, but anything can happen.



And, well, I loled at the "oh everything in ME universe is unrealistic" post XD

[adam_grif]

The speed of light is not instantanous as we all know, so if B is
observing the clock of A, it's really observing some event in A's past
(time dilation), but not really A's "now".

Since A and B synchronized their clocks at the starting line and agreed to count backwards from 8, light lag is not a factor here. Although, thanks to the bizarro time paradox stuff going on, it's entirely possible for A to see events that didn't end up happening in the final version of the timeline (after the return fire).

A would actually register that bullet hitting at 4 + 8 x 0.866s, or around 13 secs after departure by A's clock.

That's how long it would take for the light to reach him, yes, but since the speed of light is known he can just punch some simple numbers and work out that the bullet did indeed strike as soon as he pulled the trigger. But this is just the first shot fired, yes?

Once we factor the return fire exchange, a third party observer sitting next to B will see things like this (he's also synched with the other two):

- 8 (start moving)
- 7 (moving)
- 6 (bullet from B strikes and kills A)
- 5
- 4 (bullet streaks past from A) (B returns fire)
- 3
- 2
- 1 (A fires initially)

so how can firing an instantaneous bullet hit that other person at your
local perception of "now"? We just defined that "now" is a local event,
not a universal event.

It not making sense is why you can't have instantaneous travel in real life

The idea is that everybody's idea of Now, despite conflicting with each other, is valid. If you shoot something at lightpeed between the same two observers, by the time it gets there all observers will agree with the sequence of events that transpired. As soon as you exceed C, the calculations fail, observers disagree on what happened when, and the system collapses in on itself.

There must be fairly basic premise here that I'm wrong with, because what I'm saying seems to make clear sense to me.

It just seems that you're still thinking with portals with an absolute objective present, then getting frustrated when the thought experiment treats it as though it's not there. Don't concern yourself with being confused by it, because even people who claim they fully get it don't. Our brains don't come factory shipped with relativity.

[TheUnusualSuspect]

Knoll Argonar wrote...

You people are just getting the topic too far.

We're just trying to figure out if FTL travel really does cause space-time paradoxes, and if so, that absolutely prevents the possibility that FTL is even possible.

I postulate that it doesn't cause a paradox, and I'm asking for people with more knowledge and understanding than I to explain how I'm wrong.  If I'm wrong, FTL travel is impossible.  If I'm right, it's possible, just that we haven't yet figured out how to do it.

[Vaenier]

Best way to get around paradoxes is wormholes. You never exceed the speed of light, you just make the trip alot shorter instead

[adam_grif]

Vaenier wrote...

Best way to get around paradoxes is wormholes. You never exceed the speed of light, you just make the trip alot shorter instead

It's not having a velocity faster than C that causes the paradoxes, it's beating light there in a race that causes the problems. The actual method is irrelevant. Wormholes and Warp drives (which move space instead of the person in the space) both still give it hard in the ass to Causality.

[Knoll Argonar]

TheUnusualSuspect wrote...

Knoll Argonar wrote...

You people are just getting the topic too far.

We're just trying to figure out if FTL travel really does cause space-time paradoxes, and if so, that absolutely prevents the possibility that FTL is even possible.

I postulate that it doesn't cause a paradox, and I'm asking for people with more knowledge and understanding than I to explain how I'm wrong.  If I'm wrong, FTL travel is impossible.  If I'm right, it's possible, just that we haven't yet figured out how to do it.

Hey, i'm with you, I think FTL MAY be possible, if something undiscovered like mass effect fields (though these would break modern rules,but as I said, it already happened a few times in history) or new radiations exist somehow.

But I don't think some videogame forum is a good place to talk about space-time paradoxes and such.

Anyway, i'm curious about something: I know this time-paradox quite well I think, but as far as I know they only talk about near C or C speeds, not about >C speed, because that's supposed to be impossible from start. What does exactly say that Space-time paradox like exposed would happen if, you know, ignore Einstein for a bit?

[Vaenier]

if time slows for you as you go faster aproaching light speed, and if you go faster then light, you go back in time, why not just go 100.000001% light speed? you would basically end up at your destination instantly, right?

[TheUnusualSuspect]

Thanks griff, I think I'm starting to get it. The synched at start thing. B isn't looking at A's clock, he's just firing at 8 seconds on his clock, which is really 4 seconds on A's clock.

Ok, that I get now.

It does, however, beg this question (talking about relatively now, and not FTL travel).

How can both (A clock is 8 secs, and B clock is 4 secs) and (B clock is 8 secs and A clock is 4 secs), be simultaneously true (without even considering FTL travel)? That, to me, is a paradox in itself.  I understand that it's true within their own personal frames of reference, but any signal/information/object that departs A or B's frame of reference is no longer subject to A or B's frame of reference.

Consider this example: If B fired a probe towards A at B's time of 8 secs, at precisely the speed of light (or extremely close to it), time effectively stops for the probe. Within the probe's frame of reference, it reaches A instantly (due to time dilation), correct?

So, if the probe took an image of A's clock at the moment that it reached A, what would it see A's clock time as being? 4 secs, or 13 secs? If it's 4 secs, then A fires a response probe at the speed of light back towards B, and B sees A's probe arrive before it launched its probe.

Where I'm going with this is that even at relativistic speeds, the paradox appears to exist.

Modifié par TheUnusualSuspect, 01 mars 2010 - 01:08 .

[madisk]

Fourth dimension in space. "Bend" the space on top of itself to get to a new location.

[wolf99000]

Vaenier wrote...

Best way to get around paradoxes is wormholes. You never exceed the speed of light, you just make the trip alot shorter instead

do wormholes even exist I mean have we ever found any evidence that there is such a thing

[adam_grif]

Consider this example: If B fired a probe towards A at B's time of 8 secs, at precisely the speed of light (or extremely close to it), time effectively stops for the probe. Within the probe's frame of reference, it reaches A instantly (due to time dilation), correct?

No, not instantly, the time dilation factor would need to be infinity for that to happen. Iirc it wouldn't look like you were going a bajillion miles an hour, it would just look like everybody else was practically frozen in time.



Once it docks with A, it has to match speed and velocity, and now shares a frame of reference. Now going at normal speed everything has renormalized, and ~7 seconds has elapsed since it left from B. Time dilation shifts your frame's perception of time, but doesn't allow you to beat the clock and get there before you left. The amount of time that passed between when you left and when you got there @ ~lightspeed is the exact amount of time it would have taken for a beam of light to get there according to an observer at the launch point or destination.

[Jax Sparrow]

 Element Zero 'eeZo' is just one of many ways to achieve the technology represented as Mass Relays ingame.  There are already several mathematical formulas that would give us a hint on how to achieve faster than light travel this way if we could figure out how to manipulate gravity.  However, ingame they say we took the easy way out and are using Element Zero.  Whether it is a Warp Reactor and Warp Coils or Element Zero is irrelevant to the overall requirement of manipulating gravity.

There are other theoretical ways of achieving faster than light travel.  The Legion and Nazara quote regarding technological advancement upon predetermined paths explains why we only see one system ingame.  Which is akin to why they protectively ignore the Keepers.

And wouldn't it be Illium: CSI? or... whatever the name of the city is with the starport.

Edit ---  C.S.I.: Nos Astra
Yeah that probably would be a 'Crime Drama' I might actually watch.

Modifié par Jax Sparrow, 01 mars 2010 - 02:34 .

[adam_grif]

I didn't make the picture, it's more about the CSI photoshop thread that's going around. I'd like to see CSI: The Wards though.