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View Full Version : Warp drive/conventional drive question...

Durakken
2008-Nov-14, 01:37 PM
Let's say there is a star roughly 8ly away that 2 ships are going to to colonize and they travel parallel to each other...

Ship A uses a Conventional Drive to achieve a speed of 2x light speed
Ship B uses a Warp Drive to achieve a speed of 2x light speed

What happens? Ship A should take like 80 years of normal time to get there, but assuming they travel at the same speed wouldn't they get there at the same time?

sabianq
2008-Nov-14, 01:55 PM
i would asume that this question should be in the ATM section or Off Topic section.

mostly because i would wager that,

A: a conventional drive cannot exceed the speed of light,
and
B: that a warp drive does not exist yet.

LotusExcelle
2008-Nov-14, 01:57 PM
Is this a Trek question?

Argos
2008-Nov-14, 01:59 PM
I doubt the concept of 'speed' could be applied to warp drive.

Durakken
2008-Nov-14, 01:59 PM
While neither exist there are theories about what happens when you go faster than light and warp drive is theoretically possible...It's not against the mainstream... It's a question of what happens when both things happen at the same time...

LotusExcelle
2008-Nov-14, 02:02 PM
Hmmm. Simply put neither going the speed of light nor warp drive is possible. Particularly conventional drives reaching or exceeding SOL is not possible.

Durakken
2008-Nov-14, 02:05 PM
Well with warp... timespace is bent...things inside the bubble happen at the same time as things outside the bubble. It does take time to get to the place still... It would take them 4 years to get there either way...

On the other hand Relativity would mean that time is slowed on the ship so that it takes 4 years on the ship, but several times longer... but the ships would be going at the same speed?

Would Ship A arrive and find an 80+ year old colony? And how would that look from the warp ship... would it look like the ship is actually moving really slowly, 1/10 the speed of light?

NEOWatcher
2008-Nov-14, 02:06 PM
Ok; let's say we stretch the imagination into a Star Trek technology mode. It still leaves questions on the question.
What is "normal time"?
How do we get 80 years?

Durakken
2008-Nov-14, 02:08 PM
80 years is just a time i threw out... it's not a real number, but it would still be some longer time than percieved on the ship...

Normal time is the time that passes normally on earth.

Jeff Root
2008-Nov-14, 02:19 PM
Let's say there is a star roughly 8ly away that 2 ships are going to to
colonize and they travel parallel to each other...

Ship A uses a Conventional Drive to achieve a speed of 2x light speed
Ship B uses a Warp Drive to achieve a speed of 2x light speed

What happens? Ship A should take like 80 years of normal time to get
there, but assuming they travel at the same speed wouldn't they get
there at the same time?
Let's be more specific.

Ship A uses Jeffinagle Drive to achieve a speed of 2x light speed
Ship B uses Rootski Drive to achieve a speed of 2x light speed

Now you tell me what happens with those two drives I just made up.
Do they arrive at the same time? Do the passengers on ship A feel
like they've been turned inside out? Do the stars rush by ship B in
a blur? You know as much about how the Jeffinagle Drive and the
Rootski Drive work as any physicist. You tell me what happens.

-- Jeff, in Minneapolis

NEOWatcher
2008-Nov-14, 02:25 PM
80 years is just a time i threw out...
So let's leave it in the receptacle you threw it out in. :)

it's not a real number, but it would still be some longer time than percieved on the ship...
If it's 8 ly away, then anything faster than light speed from the point of view of the stationary observer on earth would see it reach there in less than 8 years time.
If you tie 2x ly to the speed as observed by the stationary observer (of course that doesn't have basis in known science) then it will take 4 years.

Normal time is the time that passes normally on earth.
Whether we are talking real relativistic speeds, or sci-fi type of speeds, if the same person is measuring the speeds, times and distances, then they will always be the same no matter how the moving person/item is experiencing.

So; I suspect that the real question would be what kind of effect is experienced by someone within a warp bubble vs someone going the same speed who's not in a warp bubble.
If we can stretch our imagination to a Sci-fi warp drive we might be able to come up with some ideas based on computations below light speed.
That's where I can't help.

If I'm interpreting your thoughts right, this seems based on Sci-fi concepts and might belong in the media section with maybe a reference to the Sci-fi drive being used.

Durakken
2008-Nov-14, 02:30 PM
v.v It would be nice if a bunch of intelligent people would act I dunno civil.

A conventional drive is a drive that uses regular thrust to get to whatever speed they get to... Obviously there is some sort of inertia dampener or way to avoid the problems those speed would have naturally on the human body...

A warp drive is a drive that creates a bubble around the ship of regular space while in front of the ship the space is compressed and the back of the bubble is expanded. back to regular space.

A conventional engine possible of those speeds is possible but not logical to do
A warp engine is also possible but takes more energy than what is in the universe apparently

This isn't a question of whether it is possible but rather of what happens when they are used at the same time...

LotusExcelle
2008-Nov-14, 02:34 PM
Hmmm. I'll restate that a conventional drive (chemical, ion, etc) is NOT capable of hitting or exceeding SOL.

Beyond that - consider that a conventional drive would need to accelerate and decelerate.

grant hutchison
2008-Nov-14, 02:43 PM
v.v It would be nice if a bunch of intelligent people would act I dunno civil.Your question is: "What would happen if [impossible physics] and [unknown physics] were used at the same time?"
The responses you've received are about as good as it's going to get, I'd say. :)

Grant Hutchison

LotusExcelle
2008-Nov-14, 02:46 PM
What would it sound like if a dragon ate a wizard? What if there was a wyrm next to the dragon eating a sourcerer? Kind of the same thing.

ravens_cry
2008-Nov-14, 02:48 PM
The theoretical Alcubierre Drives may allow one to arrive faster then the time takes light takes, when light takes the conventional path. Unfortunately, it needs things like exotic matter and negative energy, in amounts that are, to put it mildly, prohibitive. I have heard estimated saying that the amount of energy needed would exceed the amount in the known universe, hardly cost effective.
As for a conventional drive (you mean rockets, right?) going two times light speed, I am sorry, it isn't happening. If something is made of matter, both anti and pro, it can't beat, or even keep pace with, light going on the same trip. It's frustrating to all us wannabe starship captains, but that is the way the universe works. I wish it otherwise, but wishing doesn't bend the laws of physics.

LotusExcelle
2008-Nov-14, 02:50 PM
Well this is why sci-fi offers up things like the warp drive mentioned in the OP or, for example, hyperspace and such. The problem is that everyone can have any answer for what things look like or act like for such drives as they are sci-fi... not real... and therefore anything can happen especially if it fits into the plot.

Durakken
2008-Nov-14, 02:55 PM
Ok let's say they only go 1/2 the speed of light.

Now the conventional engine works
and the warp engine can get fuel from some unknown source.

the question remains unchanged.

How would the ships view each other and what would happen when they arrive?

grant hutchison
2008-Nov-14, 03:06 PM
So two ships that have accelerated using different means of propulsion fly parallel to each other at the same speed?
They'll see each other at rest, and arrive at their destination at the same time. The elapsed time measured aboard the ships will be shorter than the time measured on Earth, but not dramatically so at half lightspeed.

Grant Hutchison

Jeff Root
2008-Nov-14, 03:09 PM
Durakken,

You'll still have to tell us. You are the one who is deciding what
properties these "drives" have, so you are the one who has to decide
what their effects are. Only you know. We don't. Nobody else does.

-- Jeff, in Minneapolis

Durakken
2008-Nov-14, 03:11 PM
What about the time dilation that would happen on Ship A but not on Ship B

cjameshuff
2008-Nov-14, 03:13 PM
Ok let's say they only go 1/2 the speed of light.

Now the conventional engine works
and the warp engine can get fuel from some unknown source.

the question remains unchanged.

How would the ships view each other and what would happen when they arrive?

Now you're asking about the difference between something possible and something completely unknown. Better, but still not answerable.

If FTL is possible, then time travel and paradoxes are possible. Time dilation is quite thoroughly verified, and there's no apparent way to reconcile it with FTL that makes time travel and paradoxes impossible. The most likely conclusion is that FTL is not possible, making your question unanswerable. If it is, your question is unanswerable because it either allows paradoxes with no known resolution or a completely unknown mechanism for avoiding such paradoxes.

The Alcubierre drive can theoretically allow an object to "travel" faster than light. However, there's no known way to form the Alcubierre "bubble" at the beginning of the trip, and destroying it at the end is impossible...similarly to how information can not escape from within the event horizon of a black hole, the contents are causally separated from the outside. The apparent answer is that the ship using the Alcubierre drive sees nothing and will never be seen by anything outside, you may as well consider it to have been permanently removed from the universe.

grant hutchison
2008-Nov-14, 03:17 PM
What about the time dilation that would happen on Ship A but not on Ship BThat's really up to you. It's your warp drive.

Grant Hutchison

Delvo
2008-Nov-14, 04:15 PM
If the "B" ship's "warp field" somehow protects it from time dilation, I presume you mean its time would proceed the same as it does at the point they started from just as if it had never left. In which case the question is just another way of asking about the difference between that starting point's time and the time on ship "A". In that case, it's a fairly standard relativity question about a traveling observer and a stationary observer, and there's no need for a second ship whose time just happens to match the stationary one's time.

I suppose you might instead mean that ship "B" travels as if there were no relativity, in a universe where time is constant & universal as we thought it seemed before relativity. In that case, the question is just another way of asking how relativity is different from constant, universal time and thus how our relativistic universe is different from the way it would be if time were constant & universal. But then the two ships would be in two different universes, not flying right next to each other in the same one, so it's not the situation you described, so I suspect this isn't quite what you meant.

eburacum45
2008-Nov-14, 04:18 PM
Durakken has mentioned that a warp drive ship would not undergo time dilation. There is some justification for that idea, as Alcubierre has said that his idea for a warp-ship exists outside normal space-time so would not have to obey relativity.

http://www.npl.washington.edu/AV/altvw81.html

For those familiar with usual rules of special relativity, with its Lorentz contraction, mass increase, and time dilation, the Alcubierre warp metric has some rather peculiar aspects. Since a ship at the center of the moving volume of the metric is at rest with respect to locally flat space, there are no relativistic mass increase or time dilation effects. The on-board spaceship clock runs at the same speed as the clock of an external observer, and that observer will detect no increase in the mass of the moving ship, even when it travels at FTL speeds. But I wouldn't like to promote the idea that the Alcubierre drive is hard science- it is, rather, an interesting concoction.

ravens_cry
2008-Nov-14, 04:43 PM
Well. . .I would put it under the same heading as wormhole travel or a recent idea for a limited time machine involving lasers, a neato hypothetical derived from equations that have done a great job so far at explaining the universe as we know it.

Durakken
2008-Nov-14, 04:55 PM
The problem I'm having with this is that Ship A and Ship B if we keep their speeds constantly equal one would experience time dilation and the other wouldn't...

You would say that if a ship went from earth to it's closest neighbor and returned the crew of the ship would only experience 16 years of life but time on earth would have passed several times that...

Now if the second ship is a warp drive ship that ship would experience 16 years of life and time on earth would have passed 16 years...

If they both did this journey at the exact same time... even though they are both going the same "speed" it would seem to me that ship A, when viewed by a Ship B would have to be going vastly slower for this to be happening... So would Ship A really be going 1/2 the speed of light?

grant hutchison
2008-Nov-14, 04:59 PM
But I wouldn't like to promote the idea that the Alcubierre drive is hard science- it is, rather, an interesting concoction.Yes, calling the Alcubierre metric a "drive" is in fact a wild overstatement, like calling the Kerr metric a "time machine".
For the reasons cjameshuff describes, the Alcubierre metric is very, very far indeed from being a means of picking up a material object at point A and depositing it at point B.

Grant Hutchison

cosmocrazy
2008-Nov-14, 05:13 PM
Lets just say that somehow the conventional ship reaches C. Then the only time experienced for the crew of that ship would be the time taken to accelerate up to then down from C. The total distance traveled as measured by them would be the distance it took to accelerate then decelerate, regardless the distance they traveled and as measured by a relative observer. The crew would find that they had recorded a instant "hyper-jump" at the point of reaching C. between these 2 distances (acceleration to deceleration). For the crew of the warp drive ship their measured distance would be the 8 light years they had traveled at half the time light would take. 4 years. the conventional crew would have aged for the acceleration to deceleration time. The warp drive crew would have aged 4 years. The same distance + time traveled would be measured for them both by a stationary relative observer to them both.
I think.

cjameshuff
2008-Nov-14, 05:27 PM
If they both did this journey at the exact same time... even though they are both going the same "speed" it would seem to me that ship A, when viewed by a Ship B would have to be going vastly slower for this to be happening... So would Ship A really be going 1/2 the speed of light?

To put it simply, you can not construct an internally consistent rule system that incorporates all of relativity and FTL (or time dilation-less) drives or communication. You can ignore the inconsistencies or limit how accurately your system follows relativity, the approach typically taken in SF that includes FTL. For example, if you use an absolute rest frame, with time dilation depending on speed relative to that frame rather than to any other frame, you can define a global time and avoid time travel, etc, while keeping both FTL and time dilation. This conflicts with relativity and does not reflect reality, but might be acceptable for a system of story or game mechanics that would otherwise either lack FTL or would be filled with characters who have for some inconceivable reason have never tried to exploit their transportation for time travel.

Or you can throw out causality and let time travel and paradoxes occur. This can be interesting and strange, but would be very difficult to pull off well. Stephen Baxter apparently does this in his Xeelee novels, which I have been meaning to read someday...

Durakken
2008-Nov-14, 05:27 PM
a stationary observer would see them travelling both at the same speed?
an observer from ship B would see it as going slower?
an observer from ship A would see ship B as going?

But what about if the stationary observer is on earth able to see both for the entire duration of the flight...how can you explain that one comes back earlier than the other?

grant hutchison
2008-Nov-14, 05:28 PM
You would say that if a ship went from earth to it's closest neighbor and returned the crew of the ship would only experience 16 years of life but time on earth would have passed several times that...

Now if the second ship is a warp drive ship that ship would experience 16 years of life and time on earth would have passed 16 years...

If they both did this journey at the exact same time... even though they are both going the same "speed" it would seem to me that ship A, when viewed by a Ship B would have to be going vastly slower for this to be happening... So would Ship A really be going 1/2 the speed of light?It seems like the resolution to your problem is that the journey takes sixteen years on Earth for both ships. But one ship returns containing a crew that has aged less than sixteen years; the other returns containing a crew that has aged sixteen years.
As Delvo points out, the crew that is miraculously isolated from time dilation just age at the same rate as the observers on Earth. Presumably they're also isolated from relativistic length contraction, and see themselves covering the full eight light years during their sixteen-year flight, just as the folk on Earth observe. Whereas the other crew, subject to time dilation, also observe relativistic length contraction, and find that they cover less than eight light years in less than sixteen years. Everyone measures the velocity as half lightspeed.

Grant Hutchison

cosmocrazy
2008-Nov-14, 05:33 PM
One of the other things to consider for the conventional drive ship is flight control. At the point that ship reached C for the crew aboard distance and time becomes zero. So they would just instantly crash straight into what ever lay in their flight path or into the object of their destination from their reference frame. To over come this the ship would have to be controlled by a relative stationary controller. But here again lies a problem. at the point the ship reaches C any signal sent to control it would never get there. So really the best we could hope for is a very close percentage of C which is at least theoretically possible although extremely difficult to achieve.

Durakken
2008-Nov-14, 09:05 PM
grant the thing with that is that it doesn't work like that...

The ones in the conventional drive ship would perceive 16 years passing and it would be longer to the outside world. It wouldn't be shorter to them and the outside world experience 16 years so it's not a correct answer >.>

grant hutchison
2008-Nov-14, 10:20 PM
grant the thing with that is that it doesn't work like that...

The ones in the conventional drive ship would perceive 16 years passing and it would be longer to the outside world. It wouldn't be shorter to them and the outside world experience 16 years so it's not a correct answer >.>Thing is, it really does work like that. Absolutely no doubt about it. :)

Under special relativity, your time dilation factor is 0.866 for half lightspeed.
If you travel eight light-years at 0.5c, it will take 16 years according to external observers, but only 16x0.866 = 13.86 years by your own reckoning.
However, you'll observe those eight light-years to be contracted to 8x0.866 = 6.93 light-years.
In your 13.86 years aboard ship you will travel 6.93 light-years by your own measurements, at a velocity, by your own estimate, of 6.93/13.86 = 0.5c.
It hangs together.

Grant Hutchison

Durakken
2008-Nov-14, 10:23 PM
I see... that makes sense.

mugaliens
2008-Nov-15, 12:13 AM
Let's say there is a star roughly 8ly away that 2 ships are going to to colonize and they travel parallel to each other...

Ship A uses a Conventional Drive to achieve a speed of 2x light speed

This is impossible, ie, non-existent. Thus, there can be no informed commentary on something that doesn't exist.

Ship B uses a Warp Drive to achieve a speed of 2x light speed.

This is purely imaginative and speculative, as no known faster than light means of travel exists. Thus, any commentary on this as yet to be (if ever) discovered means of propulsion would similarly be imaginative and speculative.

What happens? Ship A should take like 80 years of normal time to get there, but assuming they travel at the same speed wouldn't they get there at the same time?

There is no comparing something that does not exist (impossibility) to another. Comparing something imaginative and speculative to another is itself imaginative and speculative.

Comparing something that does not exist/impossible to something imaginative and speculative is like comparing finding the end of infinity to an 11-story tall Stay Puft Marshmellow Man.

An interesting aside - so clever was his characterization in the movie Ghostbusters, that most people never realized that both the Stay Puft Marshmellow man character and the company, were fictitious - they only existed in the movie, never in real life.

astromark
2008-Nov-15, 12:37 AM
For the sake of your question I shall disregard the laws of this universe....
A star 8 l/y away and two ships going there,. One propelled through space by a thrust engine, while the other uses some form of 'warp' engine. Assuming proper care with the human body's ability to withstand acceleration rates are factors here then why do you think any thing would or could be different ? If both ships leave at the same time and travel at the same rate... yes they would arrive together and at the same time and would be seen to have done so from any place abserving... All this 'what if' stuff is really up to you, the fiction writer. Thats the whole idea behind a work of fiction...It is not real. You Can break all or most of the rules. You do not, and in this case can not be correct. It is NEVER possible. Please your self. What you think and write is so.