Flying to replace driving?

[Khan]

What? Surely all my physics education wasn't folly enough to think that the speed of light can't be broken. Even achieving 3x10^8m/s (right?) is very hard to do in laboratory conditions, hence the uncertainty around graviton research.

[Dunenewt]

Oops, the link above was supposed to be:

http://en.wikipedia.org/wiki/Varying_speed_of_light

Khan:

Things which can travel faster than c

[edit] Wave velocities and synchronized events

It has long been known theoretically that it is possible for the "group velocity" of light to exceed c.[11] One recent experiment made the group velocity of laser beams travel for extremely short distances through caesium atoms at 300 times c. In 2002, at the Universit

[SandChigger]

Yes, but the point is: no information can be transmitted or matter travel faster than c. (In fact, no subluminal object can even be accelerated up to c.)

[Edric O]

SandChigger is correct. All the things mentioned in that wikipedia article are in a sense "cheating" - the thing traveling faster than c is not actually matter or information.

In fact, the law of causality strictly forbids faster-than-light travel for matter or information, since faster-than-light travel is equivalent to travel back in time (because of the behaviour of time and space under general relativity, if you could travel faster than light from point A to point B, then from B to C and finally from C back to A, you could arrange it so that you return to A before you left; if it were possible, that would create all the known paradoxes associated with time travel).

(In fact, no subluminal object can even be accelerated up to c.)

True, but you can accelerate an object to speeds that asymptotically approach c. You could for instance travel at 299,792.457 km/s (and cross the galaxy in a time that, from your perspective, amounts to just a few seconds ;) ).

[Caid Ivik]

I would prefer something like this, cheaper fuel ;D

http://www.flyingmachines.org/hens.html

[SandChigger]

True, but you can accelerate an object to speeds that asymptotically approach c. You could for instance travel at 299,792.457 km/s (and cross the galaxy in a time that, from your perspective, amounts to just a few seconds ;) ).

IFF you have access to infinite energy, you can, you mean. ;)

The speed you mention is about 0.9999999966643592 c. I believe that means that in one year you'll travel the equivalent of 12,243 light years in the rest frame, so it'll still take you a bit over eight years to cross the galaxy. Best pack a lunch and change of undies. Or two. :D

[Dunenewt]

This reminds me of an essay I read, could have been by Stephen Hawking, I can't remember, but it was talking about time passing slower, the quicker you went.

[SandChigger]

The faster you go, the slower your clock appears to run to a non-moving observer. (You, of course, notice no change.)

Clocks also run slower at the bottom of (or lower in) a gravity well. That's why they build the clocks in satellites to run a little slow...so they'll stay in synch with those on the Earth's surface. ;)

[Dunenewt]

Really?  Because I read an essay once, I think it was something like a Star Wars version of the Science of Dune book, and it said that although they were twins, they would be different ages because Luke had spent his time on one planet, whilst Leia travelled on star ships quite a lot, and the closer you get to c, the slower time passes.

[Edric O]

The speed you mention is about 0.9999999966643592 c. I believe that means that in one year you'll travel the equivalent of 12,243 light years in the rest frame, so it'll still take you a bit over eight years to cross the galaxy. Best pack a lunch and change of undies. Or two. :D

Ok, so I didn't do the math. Close enough. :P

One idea I read about is that, if you have enough energy to begin with, and a way to store it, you could have relativistic shuttles going between solar systems with very little additional expense of energy per flight beyond the initial investment. It goes like this: At point A you invest X amount of energy to accelerate the shuttle to relativistic speeds. At point B, your destination, you decelerate back into the rest frame and store most of the kinetic energy you lost into some sort of energy storage device. You can then use that stored energy again for your return journey, and so on back and forth like a ping-pong ball. Of course you wouldn't get 100% efficiency, so you'd need some new energy input for each journey, but with high enough efficiency this new energy input can be kept rather small.

The acceleration/deceleration device at each end of the journey would probably look like a giant tube or cannon, and it would have to be extremely long because it would take a long time to get to relativistic speeds at an acceleration the human body can endure (around 10 m/s^2).

Really?  Because I read an essay once, I think it was something like a Star Wars version of the Science of Dune book, and it said that although they were twins, they would be different ages because Luke had spent his time on one planet, whilst Leia travelled on star ships quite a lot, and the closer you get to c, the slower time passes.

Yes, that's true, in the sense that if you get closer to c, the time that seems to you to be one hour is longer than an hour for people in the rest frame.

For example, the diameter of the Milky Way galaxy is about 100,000 light years. At a speed of 0.9999999966643592 c, it would take you over a hundred thousand years to cross the galaxy, from the point of view of an observer outside your ship (such as the people on the planet you left behind). But, as SandChigger calculated, from your point of view only a little over 8 years would pass. So for every year that you experience, 12,500 years pass in the outside universe.

This effect can of course be used to create a sort of one-way time travel into the future.

[Dunenewt]

Ok, so I didn't do the math. Close enough. :P

One idea I read about is that, if you have enough energy to begin with, and a way to store it, you could have relativistic shuttles going between solar systems with very little additional expense of energy per flight beyond the initial investment. It goes like this: At point A you invest X amount of energy to accelerate the shuttle to relativistic speeds. At point B, your destination, you decelerate back into the rest frame and store most of the kinetic energy you lost into some sort of energy storage device. You can then use that stored energy again for your return journey, and so on back and forth like a ping-pong ball. Of course you wouldn't get 100% efficiency, so you'd need some new energy input for each journey, but with high enough efficiency this new energy input can be kept rather small.

The acceleration/deceleration device at each end of the journey would probably look like a giant tube or cannon, and it would have to be extremely long because it would take a long time to get to relativistic speeds at an acceleration the human body can endure (around 10 m/s^2).

Would a mass driver do the job?

[SandChigger]

The acceleration/deceleration device at each end of the journey would probably look like a giant tube or cannon, and it would have to be extremely long because it would take a long time to get to relativistic speeds at an acceleration the human body can endure (around 10 m/s^2).

What percentage of c are you thinking of? At 9.81 m/s^2 it's going to take you about 318 days to get to 0.9 c. That's a fairly impressive tube you're going to need. ;)

Mass driver, huh? On the ship you mean, right?

[Dunenewt]

What if the people were sedated?  Would higher acceleration be possible then?

[SandChigger]

:O

If you don't mind my asking, what are you majoring in at uni?

(I'm gonna guess it's nothing science related, right? ;) )

Um...let's see...where to start?

An acceleration of 9.81 m/s^2 is equivalent to one gee. (Put one person in a cubicle with no windows on the surface of the Earth and another person in an identical cubicle on a spaceship accelerating in the direction of the cubicle ceiling at 9.81 m/s^2 and both will experience an equivalent "attraction" to the floor of their cubicle. Neither will be able to tell if they are on Earth or in an accelerating ship.)

An acceleration greater than the above will feel like an increase in gravity. At 2 gee you would feel like your body weighed twice as much. I don't recall what the tolerance is, but more than a few gee will kill you. Your bones will fracture, unable to support their own weight, and your other tissues lose their integrity. At a sufficiently high acceleration, you become a greasy layer along the floor or walls. Unless we discover a cheap and efficient means of generating and manipulating gravitational fields, "inertial dampening"

[Dunenewt]

:O

If you don't mind my asking, what are you majoring in at uni?

(I'm gonna guess it's nothing science related, right? ;) )

Um...let's see...where to start?

An acceleration of 9.81 m/s^2 is equivalent to one gee. (Put one person in a cubicle with no windows on the surface of the Earth and another person in an identical cubicle on a spaceship accelerating in the direction of the cubicle ceiling at 9.81 m/s^2 and both will experience an equivalent "attraction" to the floor of their cubicle. Neither will be able to tell if they are on Earth or in an accelerating ship.)

An acceleration greater than the above will feel like an increase in gravity. At 2 gee you would feel like your body weighed twice as much. I don't recall what the tolerance is, but more than a few gee will kill you. Your bones will fracture, unable to support their own weight, and your other tissues lose their integrity. At a sufficiently high acceleration, you become a greasy layer along the floor or walls. Unless we discover a cheap and efficient means of generating and manipulating gravitational fields, "inertial dampening"

[SandChigger]

There's some surprising data here:

http://en.wikipedia.org/wiki/G-force

Duration of exposure seems to be a factor.

[Dunenewt]

Yeah, in crashes several people have experiences over 100G.

So perhaps if the initial acceleration was pretty massive, but for only a split second before decreasing...

[D2k Sardaukar]

How can you get from the subject 'flying to replace driving' to 'speed of light' and G-force?

[Dunenewt]

Well Edric said he'd rather have maglev trains than planes, and then it spoke about their theoretical top speed in a vacuum, which was the speed of light...

[Hypatia]

Science-oriented topics can wander all sorts of places. That's how a lot of scientific discoveries get made. ;)

Personally, I'm waiting for somebody to invent the transporter. Failing that, I wouldn't mind being able to fly -- not in a plane (been there, done that, didn't really care for it)-- just me.

[SandChigger]

You do realize that a Star Trek "transporter" (or Puppeter stepping pad or posthuman fax or stargate, even) is a death-machine that just produces a copy that thinks it's you, right?

[Hypatia]

Not all of us are afraid of the unknown. ::) Mind you, if the essentials that make me myself are left intact, it doesn't matter if the process should duplicate me in less than 100% perfection... I could do without my various allergies. I wouldn't mind being an inch or two taller.

I'd even be happy if I woke up one morning with the ability to teleport.

[SandChigger]

It's not a matter of fear of the unknown, but one of <b>actually thinking</b> things through to their logical conclusion.

Remembering that this is a Dune-related board, it's the same problem as that "datapacket" that Omnius Prime beams out in the "flash of light" signal in <i>Bottle of Corny-oh!</i>: unless a teletransportation device opens some sort of pathway between two points in spacetime that allows a traveller or object to pass intact, bodily, from one to the other, then it must necessarily analyze/disintigrate the traveller into some structural representation (data) for transmission to the destination. The actual atoms are not sent (have fun accelerating them to lightspeed) and the traveller reconstructed using them...so YOU don't actually go anywhere. You die and a clone built from the specifications of the data signal steps out at the destination thinking it's you. It's worse than a reawakened ghola...because there's no part of the original there.

(I was never one of those who got into the Star Trek technical manuals. If they explain the transporter using some sort of "matter stream" or the like (disassembling and sending the actual matter), then they're full of crap, 'cause that ain't ever going to happen. And reconstruction of an object at a distance without a reception device is equally ludicrous.)

An ability to teleport, though, now THAT is perfectly possible.

In the fantasy universe of the New Dune, I mean. ::)

[Hypatia]

If you re-read my first post, you'll note that I used the word "transporter" in the generic sense, not the 'Star Trek' sense. Even on Star Trek they had discussions about whether one's first experience in a transporter destroyed the original person forever.

I just don't have a lot of faith that my local City Council, in its divine stupidity, will ever understand how important public transportation is to people who either don't drive, don't own a vehicle, or can't afford to drive. They already don't understand what a handy thing a high-speed train connection in Red Deer would be between the major cities in Alberta. Just because it's a 90-minute drive to Edmonton or Calgary doesn't mean everybody has that option. And Alberta used to have really good highways. But much depends on the priorities set by whichever premier is in power, and those we've had during the past 15-20 years have been quite uninterested in stuff as boring as maintaining infrastructure.

[SandChigger]

I added other similar devices in parenthesis in my first reply, and the Star Trek specific stuff in another in my second.

Reading is fundamental.