Warp drive may actually be possible, NASA scientist says • Hacker News Board

Re: Warp drive may actually be possible, NASA scientist says

#21

Post by shanelja » Wed, Sep 19, 2012, 12:27 PM UTC

jonnathanson wrote: post #18

shanelja wrote: post #15

Earlier quoted context omitted.

Question 2: What would happen if you, whilst within this bubble, throw a coin attached to a piece of string out of the space ship, while still connected to the ship by the string and the coin exits the bubble? For instance, assuming the 'string' was made of a tough alloy, would it snap and the coin remain where it was at that time, would the ship be dragged back to where the coin is, or can the question not yet be an…

Honestly? I'm not sure. I know there are at least a few physicists who post on HN, and perhaps one of them could provide a more informed estimation than I. Bear in mind, this article only addresses one of the many fundamental challenges to the Alcubierre drive: the energy requirements. Typically, the energy requirement has been considered the primary challenge to the feasibility of the device. But it's not the only o…

It sounds like we are as yet a long, long way away from this being a reality, but I suppose it only takes a couple of leaps forward to make it more than just 'maybe possible'.

Re: Warp drive may actually be possible, NASA scientist says

#22

Post by gus_massa » Wed, Sep 19, 2012, 12:31 PM UTC

keyle wrote: post #11

Can someone explain what happens to time while you travel this way? Is your family at home going to be older when you come back from one of those trips?

Space-time is a single entity, so it's not possible to distort the time without distorting the time. For example, if some astronauts are traveling in another rocket with a constant relative velocity (I don't know enough special relativity to do the calculations, but if this device is constructible I would expect to have huge modifications in the time coordinate. Just in case, say goodbye to everyone before leaving.

Re: Warp drive may actually be possible, NASA scientist says

#23

Post by EthanHeilman » Wed, Sep 19, 2012, 12:55 PM UTC

jonnathanson wrote: post #13

keyle wrote: post #11

Can someone explain what happens to time while you travel this way? Is your family at home going to be older when you come back from one of those trips?

Simple answer: probably not. You wouldn't experience time dilation in this scenario, because the ship itself isn't actually moving faster than light speed. In fact, it's not moving very quickly at all. It's bending space around itself, while remaining within a flat and undistorted region of space inside the bubble. With respect to objects inside the bubble (its own frame of reference), the ship is not moving faster t…

>You wouldn't experience time dilation in this scenario, because the ship itself isn't actually moving faster than light speed.

Time dilation occurs at speeds far less than the speed of light. For instance GPS satellites and jet planes experience measurable time dilation.

I am very curious about the time effects of such a drive. Does the ability to warp space using such a device necessarily include the ability to warp time? Is it possible, within a frame of reference, to locally reverse the arrow of time and thereby reverse entropy within that pocket?

>A beam of light inside the warp bubble will still travel faster than the ship, for instance.

But that beam of light seen from outside the bubble will appear to travel faster than the speed of light.

Re: Warp drive may actually be possible, NASA scientist says

#24

Post by SolarNet » Wed, Sep 19, 2012, 1:11 PM UTC

EthanHeilman wrote: post #23

jonnathanson wrote: post #13

Earlier quoted context omitted.

Simple answer: probably not. You wouldn't experience time dilation in this scenario, because the ship itself isn't actually moving faster than light speed. In fact, it's not moving very quickly at all. It's bending space around itself, while remaining within a flat and undistorted region of space inside the bubble. With respect to objects inside the bubble (its own frame of reference), the ship is not moving faster t…

>You wouldn't experience time dilation in this scenario, because the ship itself isn't actually moving faster than light speed. Time dilation occurs at speeds far less than the speed of light. For instance GPS satellites and jet planes experience measurable time dilation. I am very curious about the time effects of such a drive. Does the ability to warp space using such a device necessarily include the ability to war…

That depends on what the outside of a warp bubble looks like. Since it's bending space all over the place, it may not be observable from outside.

Re: Warp drive may actually be possible, NASA scientist says

#25

Post by [deleted] » Wed, Sep 19, 2012, 1:13 PM UTC

jonnathanson wrote: post #13

keyle wrote: post #11

Can someone explain what happens to time while you travel this way? Is your family at home going to be older when you come back from one of those trips?

Simple answer: probably not. You wouldn't experience time dilation in this scenario, because the ship itself isn't actually moving faster than light speed. In fact, it's not moving very quickly at all. It's bending space around itself, while remaining within a flat and undistorted region of space inside the bubble. With respect to objects inside the bubble (its own frame of reference), the ship is not moving faster t…

[deleted]

Re: Warp drive may actually be possible, NASA scientist says

#26

Post by jerf » Wed, Sep 19, 2012, 1:44 PM UTC

shanelja wrote: post #15

jonnathanson wrote: post #13

Earlier quoted context omitted.

Simple answer: probably not. You wouldn't experience time dilation in this scenario, because the ship itself isn't actually moving faster than light speed. In fact, it's not moving very quickly at all. It's bending space around itself, while remaining within a flat and undistorted region of space inside the bubble. With respect to objects inside the bubble (its own frame of reference), the ship is not moving faster t…

Question 2: What would happen if you, whilst within this bubble, throw a coin attached to a piece of string out of the space ship, while still connected to the ship by the string and the coin exits the bubble? For instance, assuming the 'string' was made of a tough alloy, would it snap and the coin remain where it was at that time, would the ship be dragged back to where the coin is, or can the question not yet be an…

The coin experiences massive tidal forces and basically explodes, taking a certain amount of energy out of the warp field in order to do it.

One of the problems with this approach that has been explored in other papers is that even if you have a warp drive and even if you have actually gotten a ship into it and even if you've managed to point it in the direction you want to go, the collision of the interstellar medium with your warp field tears it apart quite violently and the warp field "collapses". And unlike when they "collapse" on Star Trek and the only manifestation is a polite electronic "whirring" noise, being in a collapsing real warp field is a death sentence, with tidal forces on par with black hole gravitational fields.

Re: Warp drive may actually be possible, NASA scientist says

#27

Post by egypturnash » Wed, Sep 19, 2012, 2:19 PM UTC

WalterBright wrote: post #6

One issue about warp drives that I never see mentioned is one has to be careful one is not creating a perpetual motion device. Consider a warp drive that transports you from, say, earth's orbit to pluto's orbit. Now, you fall back towards earth's orbit. This means that the warp drive, in order to not violate conservation of energy, must require at least as much energy as the potential energy difference between the tw…

I think you're describing a feature, not a bug. Especially if you can figure out a way to derive energy from the fall.

Re: Warp drive may actually be possible, NASA scientist says

#28

Post by wcoenen » Wed, Sep 19, 2012, 2:42 PM UTC

jasonwatkinspdx wrote: post #17

wcoenen wrote: post #5

Earlier quoted context omitted.

The mass added by the "fuel" of the orion nuclear pulse drive is negligible: a nuclear bomb has very little mass compared to the impulse boost you can extract from it. You could literally lift a city-sized space ship to orbit on the cheap with this technology. The problem is the nuclear fall-out for those left on the ground.

It's not that simple. You are vastly underestimating how much scaleup is required to sustain that acceleration up until you get a reasonable trip time. Here's the summary from NASA: "Here are four examples [large graphic][1] of what it would take to send a canister about the size of a Shuttle payload (or a school bus) past our nearest neighboring star...and allowing 900 years for it to make this journey. Well....If y…

Your references are about rocket designs, which have limits to how fast they can expel reaction mass before they blow themselves up. Orion isn't really a rocket as it does the violent reaction outside of the spaceship. With Orion, the limit is how fast the pusher plate can be cooled or how much momentum can be handled by the shock absorbers.

Granted, even with fusion bombs there is still a limit to how much energy and momentum you can extract from a certain mass, so the same concerns of diminishing returns apply. But according to Dyson's numbers, a 133 year trip to Alpha Centauri might be possible[1].

Even discounting interstellar travel, a trip time of only a few weeks to Mars with current technology sure sounds interesting to me.

[1] http://en.wikipedia.org/wiki/Project_Orion_(nuclear_propulsi...

Re: Warp drive may actually be possible, NASA scientist says

#29

Post by maxerickson » Wed, Sep 19, 2012, 3:05 PM UTC

WalterBright wrote: post #6

One issue about warp drives that I never see mentioned is one has to be careful one is not creating a perpetual motion device. Consider a warp drive that transports you from, say, earth's orbit to pluto's orbit. Now, you fall back towards earth's orbit. This means that the warp drive, in order to not violate conservation of energy, must require at least as much energy as the potential energy difference between the tw…

It seems if you had the power to violate causality and worked hard enough at it, that future event would have propagated into the present day past by now.

Maybe that's really what killed the dinosaurs.

Re: Warp drive may actually be possible, NASA scientist says

#30

Post by jonnathanson » Wed, Sep 19, 2012, 3:25 PM UTC

EthanHeilman wrote: post #23

jonnathanson wrote: post #13

Earlier quoted context omitted.

Simple answer: probably not. You wouldn't experience time dilation in this scenario, because the ship itself isn't actually moving faster than light speed. In fact, it's not moving very quickly at all. It's bending space around itself, while remaining within a flat and undistorted region of space inside the bubble. With respect to objects inside the bubble (its own frame of reference), the ship is not moving faster t…

>You wouldn't experience time dilation in this scenario, because the ship itself isn't actually moving faster than light speed. Time dilation occurs at speeds far less than the speed of light. For instance GPS satellites and jet planes experience measurable time dilation. I am very curious about the time effects of such a drive. Does the ability to warp space using such a device necessarily include the ability to war…

"Time dilation occurs at speeds far less than the speed of light. For instance GPS satellites and jet planes experience measurable time dilation."

Sure, but I think (?) the original question was asking about time dilation in the massive sense: i.e., you go on a round trip to some distant point in space and return, and it's only been a few days for you, but a few hundred or thousand years have passed on Earth. That sort of time dilation.

That sort won't occur with an Alcubierre ship. It's my understanding that the ship isn't actually moving at all inside the bubble -- or, if it is, it's moving extremely slowly.