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Serenity: In space no one can hear you scream cause this movie is actually scientifically correct (ok not really)

 

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Serenity: One Captain. One Psychic. One Assasin. One Doctor. One Shepherd. Another Assasin, but different from the first. One Mechanic. One Companion, which is like a geisha or a courtesan, I guess sort of. One... um... did I do Mechanic? Which movie is this?

 

Aand my favourite:

Serenity: If you loved Katerina Witt in 'Carmen on Ice', you'll love this

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All the talk about Star Trek got me thinking, what if you could generate an artificial gravity field? I've seen gravitational pull represented by a ball resting on a sheet, the depression it forms makes for a pictorial representation of the planet's gravity field. If you could create those artificially-you could have a spacecraft with a gravity field generator built into the front area of the ship. It would create a gravitational field in front of the ship-a 'depression' so to speak that the ship would forever fall towards but never arrive to until it was shut down. It might not go faster than light but perhaps it would make for faster travel within the solar system. If you could cut the travel time to Mars down to 3 or 4 months or less with such a system it would make the idea of going there much more plausible. B)

I dont fear the dark...the dark fears me!

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What actually would happen if you travelled 50 million light years away at the speed of light and came back again, is that you would find yourself 100 million years into the future of your home planet.

THis is because as you near C, time slows down realative to you, until if you could actually reach the C itself (which you couldn't) time would stop altogeter, meaning that you could instantly travel anywhere in the universe.

Think of it like this - photons don't age, time doesn't pass for them. To us, it's takes a photon 50 million years to traverse the distance from a star that's 50 million light years away, but to the photon, the journey is instantaneous.

 

This is called the "twin paradox," because you would think if your twin stayed on earth and you traveled near light speed for a while, then came back and met up with your twin, you would have aged less than your twin, because time passes more slowly in your reference frame. But, you can choose different reference frames so that your twin is moving away from you at a velocity near c while you stand still, so time should dilate for him and you should be older than him. Paradox!

 

Like most relativity paradoxes though, it's a fallacy. The reasoning assumes the two frames of reference (moving spaceship and moving earth) are equivalent, when in fact Special Relativity says only inertial frames of reference are equivalent. An inertial frame is one where there's no acceleration. The traveling twin's frame is not inertial, because they had to decelerate to turn around and come back. That requires General Relativity to calculate what would happen. I don't claim to know anything about that, but when we were learning special relativity, the professor assured us that if you take general relativity into account, the twin on the earth ages more when you slow down and turn around, so you do in fact age less if you're the one in the spaceship, and it resolves the twin paradox.

 

Also, I just looked it up now and apparently you can explain it with spacetime diagrams and other stuff too.

 

http://math.ucr.edu/home/baez/physics/Rela...in_paradox.html

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There never was any paradox. It's not like people sat around for years trying to figure out the answer, it's pefectly obvious.

It may be correct to say that either of the twins can say the other one is moving away from them at 99.9% of c, but it's only the traveling person's frame of reference which changes, because they have to change directon and come back, and changing direction is acceleration.

The traveling person is not staying in uniform motion, they are accelerating and decelerating to and from speeds near c, while the person on earth is always in uniform motion.

Relativity only applies to bodies in uniform motion.

Civillisation will not attain perfection until the last stone, from the last church, falls on the last priest.

- Emil Zola

 

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All the talk about Star Trek got me thinking, what if you could generate an artificial gravity field? I've seen gravitational pull represented by a ball resting on a sheet, the depression it forms makes for a pictorial representation of the planet's gravity field. If you could create those artificially-you could have a spacecraft with a gravity field generator built into the front area of the ship. It would create a gravitational field in front of the ship-a 'depression' so to speak that the ship would forever fall towards but never arrive to until it was shut down. It might not go faster than light but perhaps it would make for faster travel within the solar system. If you could cut the travel time to Mars down to 3 or 4 months or less with such a system it would make the idea of going there much more plausible. B)

That's not going to happen. Gravity is just a force, isn't actually 'made' of anything. You can't generate it from nothing, and whatever matter you use to generate the gravity is also going to affect the ship.

You can already travel to Mars using existing rocket technology in a matter of 2 weeks if you go in a straight line.

Civillisation will not attain perfection until the last stone, from the last church, falls on the last priest.

- Emil Zola

 

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You can already travel to Mars using existing rocket technology in a matter of 2 weeks if you go in a straight line.

 

I think the problem with such travel is not the actual distance, but the amount of fuel needed to accelerate to that sort of speed (which increases the mass of the craft, therefore requiring even more fuel, and so on).

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There never was any paradox. It's not like people sat around for years trying to figure out the answer, it's pefectly obvious.

 

That's why I said it was a fallacy. People do actually sit around and worry about it nonetheless, because they have a little knowledge about relativity, but not enough to understand why it's a fallacy; a little knowledge is a dangerous thing.

 

Relativity only applies to bodies in uniform motion.

 

I see what you're saying, but it's technically not quite true when stated that way. Relativity still applies to non-inertial frames, it justs says they're not equivalent. So the assumptions of the twin "paradox" are faulty from the start because they assumed the two frames were equivalent, so it can't be solved like a simple problem in Special Relativity. General Relativity can solve problems involving non-inertial frames, and you can do the twin paradox calculation with General Relativity to prove that the traveling twin really does age less.

 

Apparently you can also show that the traveling twin ages more without going to General Relativity by using a 4d spacetime diagram, and Minkowski's non-Euclidian "distance formula" to give "proper time." ( dTau^2 = dt^2 - dr^2 )

 

As for going to Mars in shorter times, I think there are still a lot of projects improving propulsion systems. I don't know much about them, but the projects include: ion drives, light sails, and something using a nuclear reaction for propulsion. I'm pretty sure none of these have been tested in manned craft, so the travel time to mars could definitely be improved with existing technology. I'd be curious to know where Odd gets his figure of 2 weeks from?

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It was just an estimate. Working it out on a calculator, it's more like 40 days, if mars was at it's closest (36 million miles) and given that current rockets can do 10 miles per second.

 

Nuclear energy will probably be next, but nuclear energy is still only 1% efficient.

Civillisation will not attain perfection until the last stone, from the last church, falls on the last priest.

- Emil Zola

 

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Plasma drives are the propulsion of the future - Aussie researchers at the ESA have just developed a prototype plasma drive that provides ~10Km/s thrust with a tiny amount of fuel, no moving parts, no electrodes, and uses very little electricity. More thrust than Ion drives, less fuel than conventional rockets, relatively cheap (also only in preliminary stage of testing though). http://news.bbc.co.uk/2/hi/technology/4527696.stm

 

And you are technically correct in saying that astronomical bodies (eg Jupiter and the Sun) orbit around a common gravitational centre, though it is also OK to say that Jupiter orbits the Sun. While less massive objects always revolve around larger ones, the common centre of gravity is offset from the centre of the larger body due to the gravitational pull of the smaller body. When the two bodies are of similar size, this distinction is pretty clear - a good ecample is the Pluto/Charon situation.

 

And actually, a tenth planet was recently added to the list, though it hasn't AFAIK been named yet, I think it is substantially bigger than Pluto, and orbits quite a long way out. It is very dark (low albedo) and so is very difficult to spot.

 

Again, the definition of a Planet has been defined as a body with a common centre of gravity with the Sun - plans to drop Pluto as a planet have been rejected. Technically, Pluto/Charon should be considered as a binary planet. A planet is a body large enough to be squashed into a ball by its own mass, and shares a common center of gravity with a star. Or something like that. Pluto is always going to be on the border line of any definition - it is just wierd.

 

At the moment it is a six month journey to mars, and the round trip is two years, as it is more resonable to wait until the Earth and Mars are closest to each other to attempt the trip. And that is using gravitational slingshots around Venus and Earth, as the amount of rocket fuel required is enormous. Taking a direct line with currently in-use technology would be prohibitively expensive.

 

EDIT: I looked at the link and it isn't the one I was thinking about.... I'll try to find the one I meant :)

Edited by obscurus
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There are several asteroids which are bigger than the 400km diameter threshiold that gives them enough mass to become spherical - why aren't they called planets as well?

The first asteroid to be discovred was Ceres, and it was at first called a planet, but as other asteroids were found it was demoted. I think as many other Kuiper belt objects are found the same thing will happen with pluto. Either that, or we end up with several dozen 'planets'.

Pluto is fundamentally a Kuiper belt object, as is shown by its very small size, distance and wild orbit.

Civillisation will not attain perfection until the last stone, from the last church, falls on the last priest.

- Emil Zola

 

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Pluto is not much smaller than Mercury, and its orbit at its closest to the sun actually brings it closer to the sun than Neptune. The I dont see a problem with Ceres being defined as a planet... The problem is there are a lot of objects in the Solar system (not to mention other star systems) that just don't easily fit into any simple categories. I personally like the definition of a planet as any object with sufficient mass to be roughly spherical. Obviously that would then include the moon and a large number of planetary satellites, but all of these definitons are arbitrary anyway, so we shouldn't get too hung up on what constitutes a planet and what doesn't (after all, they are just labels - they have no practical relevance at all).

 

Perhaps Mercury should also be demoted from its planetary status - after all it is smaller than some of the moons of Jupiter and Saturn.

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Well, everyone except me - I've never been near a university.

Pluto is not much smaller than Mercury, and its orbit at its closest to the sun actually brings it closer to the sun than Neptune. The I dont see a problem with Ceres being defined as a planet... The problem is there are a lot of objects in the Solar system (not to mention other star systems) that just don't easily fit into any simple categories. I personally like the definition of a planet as any object with sufficient mass to be roughly spherical. Obviously that would then include the moon and a large number of planetary satellites, but all of these definitons are arbitrary anyway, so we shouldn't get too hung up on what constitutes a planet and what doesn't (after all, they are just labels - they have no practical relevance at all).

 

Perhaps Mercury should also be demoted from its planetary status - after all it is smaller than some of the moons of Jupiter and Saturn.

 

Eh? You said planets should be defined solely by size - if they're big enough to form a sphere, then they're a planet.

That's a stupid idea. That's like saying any living creature big enough to be a human should be called a human.

What's the difference between an object that's 390km in diamater and one that's 410km in diameter?

The only difference is that one becomes roughly spherical and the other doesn't.

Shape is no way to define a planet.

I think there should be several criteria, includng a certain mass, which means there is a certain minimum amount of gravity and therefore atmosphere, it should orbit in the same plane as the major planets and not wander in and out of another's orbit at wild angles.

It should be massive enough that it does not have to share space with hundreds of similar objects, and was able to either assimilate them while it was forming, trap them as moons, or kick them out the way the major planets have done.

Of course it doesn't really matter what you label them, but at the same time there has to be some kind of consistency. You can't have pluto being called a planet while a dozen other Kuiper belt objects, which are virtually identical, are not.

It's just an accident of history, that pluto happened to be the first Kuiper belt object discovered, and I don't think that alone gives it the right to planetary status.

Civillisation will not attain perfection until the last stone, from the last church, falls on the last priest.

- Emil Zola

 

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That's not going to happen. Gravity is just a force, isn't actually 'made' of anything. You can't generate it from nothing, and whatever matter you use to generate the gravity is also going to affect the ship.

You can already travel to Mars using existing rocket technology in a matter of 2 weeks if you go in a straight line.

Gravity may be a force, but so is magnetism and we use that in various ways dont we? We can use electricity to generate a magnetic field and use magnets in a generator along with motion to generate electrictiy so why would it be impossible to find a way to artficially generate a gravity field? I've read that some physics researchers speculate that all these forces are related to each other in some form or fashion, we just havent found the right links yet, but if we were to-surely there would be a possible technological way to generate a gravitational field without needing a large mass?

 

Imagine what we might could do with such technology!

 

1. Gravity Drive as I mentioned before.

2. Artifical gravity on spaceships-not just Star Trek anymore!

3. If we could project and control localized gravitational fields perhaps this could be the real life basis of the 'shielding' we see in the sci-fi shows-a localized gravity field outside the ship that can deflect stuff that has mass. B)

I dont fear the dark...the dark fears me!

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Generating gravity is not the same as generating electric or magnetic fields. That works because that's already the way nature works, the perpetual motion of electric and magnetic fileds generating one another is what makes light.

THe forces many all have been united once, but only at ridiculously high temperatures and pressures - the kind you only get in the fist few billionths of a second after the big bang, when all the matter in the universe was confined in a small space. There's no way that can be artifically generated.

Scientists simply don't know what gravity is, it is not generated, it just exists, and it affects everything without exception, it's also incredibly weak compared to the other forces.

Gravity is the big sticking point when it comes to theories of everything.

Maybe it will be possible in the future, maybe anything will be possible, but I'm sure it'll be very, very far in the future, and we'll have thought of other ways to travel quicky in space before that, like matter/anti-matter drives or something. THat's at least theoretically possible, the only problems being how you generate so much anti-matter, and how you store it. I guess the solution would be to generate as you need it,. so it requires no storage.

Civillisation will not attain perfection until the last stone, from the last church, falls on the last priest.

- Emil Zola

 

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Well, everyone except me - I've never been near a university.

 

We can tell ;)

 

Eh? You said planets should be defined solely by size - if they're big enough to form a sphere, then they're a planet.

That's a stupid idea. That's like saying any living creature big enough to be a human should be called a human.

What's the difference between an object that's 390km in diamater and one that's 410km in diameter?

The only difference is that one becomes roughly spherical and the other doesn't.

Shape is no way to define a planet.

 

It is a perfectly reasonable idea, if for no other reason than it is simple. Shape is as good a way to define a planet as any, and it is no way comparable to definitions of human beings (who are, by the way, defined by our shape, albeit in a much more complex way).

 

I think there should be several criteria, includng a certain mass, which means there is a certain minimum amount of gravity and therefore atmosphere, it should orbit in the same plane as the major planets and not wander in and out of another's orbit at wild angles. It should be massive enough that it does not have to share space with hundreds of similar objects, and was able to either assimilate them while it was forming, trap them as moons, or kick them out the way the major planets have done.

Of course it doesn't really matter what you label them, but at the same time there has to be some kind of consistency. You can't have pluto being called a planet while a dozen other Kuiper belt objects, which are virtually identical, are not.

It's just an accident of history, that pluto happened to be the first Kuiper belt object discovered, and I don't think that alone gives it the right to planetary status.

 

The problem with your definition is that is needlessly complex, and results in too many borderline objects sittting on the fence of planethood. And just takes too long to explain, which for something as simple as a planet is really unnecessary.

Is an object the size of earth with an atmosphere, that happens to be NOT orbiting any star, just drifting through space not still a planet? What about an object the size of jupiter captured by a star, but in a highly eccentric retrograde orbit? Planet or not?

An Earth-like planet with an atmosphere and oceans orbiting the Sun or another star on a plane 90 degrees to the eccliptic? Not really a planet?

 

I agree that consistency would be desirable, and nothing would be more consistent that a simple definition based soley on physical properties of the object, and nothing will generate less consistency than a classification scheme based on numerous arbitrarily defined parameters involving complex descriptions of orbital patterns, companion objects, atmospheric levels, frequency of similar objects in similar orbits, and with numerous exceptions clumsily derived to fudge objects that don't quite fit the criteria one way or the other into a category...

 

True, my classification scheme results in hundreds of objects being defined as planets that previously were not considered planets, but is entirely consistent and will be applicable to any star system, or even the absence of a star system, while your scheme is highly inconsistent and requires all kinds of exceptions, and is only applicable to one star system. My classification scheme can easily be explained to a child, yours would confuse even professional astronomers, and cause enormous debate about this object or that object being a planet or not.

 

Planet = any object with suficient mass to collapse into a spheroid, but small enough not to spontaneously ignite and become a star. Consistent, simple, clean and sleek. Does requre redefining some objects however.

The simpler the scheme, the better.

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It is a perfectly reasonable idea, if for no other reason than it is simple. Shape is as good a way to define a planet as any, and it is no way comparable to definitions of human beings (who are, by the way, defined by our shape, albeit in a much more complex way).

The problem with your definition is that is needlessly complex, and results in too many borderline objects sittting on the fence of planethood. And just takes too long to explain, which for something as simple as a planet is really unnecessary.

Is an object the size of earth with an atmosphere, that happens to be NOT orbiting any star, just drifting through space not still a planet? What about an object the size of jupiter captured by a star, but in a highly eccentric retrograde orbit? Planet or not?

An Earth-like planet with an atmosphere and oceans orbiting the Sun or another star on a plane 90 degrees to the eccliptic? Not really a planet?

I didn't say it has to meet all of those criteria, the problem with pluto is that it fails to meet ANY of them.

It meets your pointless shape test, and that's it.

I would probably remove the angle test, since it would probably be possible for a forming planet to be nudged badly out it's orbital angle by collisions, even though it didn't happen in this solar system.

As for things drifting through space, they certainly would not be called planets, and the chances of a planet from one star floating off and being captured by another star are so mindbogglingly remote, it's laughable even thinking about it, and as far as we know, planets do not form by themselves in deep space.

 

True, my classification scheme results in hundreds of objects being defined as planets that previously were not considered planets, but is entirely consistent and will be applicable to any star system, or even the absence of a star system, while your scheme is highly inconsistent and requires all kinds of exceptions, and is only applicable to one star system. My classification scheme can easily be explained to a child, yours would confuse even professional astronomers, and cause enormous debate about this object or that object being a planet or not.

I think you'd find - if you weren't being obtusely unfair - that it's perfectly clear. It's obvious straight away using the system that there are 8 planets in our solar system. And of course we should base the numbers on the properties of our own solar system. At this point there is no reason to assume that all solar systems dont' form in the same way, and will have very similar properties.

With that soluiton only one object currently has to be redefined, with your solution a dozen objects will have to be redefined., and we'll end up with hundreds of planets.

You're basically defining planets the way you might define eggs - have a little plastic sheet with various sized holes in it, and see which one the planet fits through.

What if a comet happens to come in that's just big enough to be spherical? It has all the properties of a comet, behaves like a comet, but suddenly it has to be popped through the egg gauge and called a planet.

WHat about ex-stars that have cooled down and become dwarfs, they can be the size of planets, and spherical, and are no longer generating their own heat - are they now planets?

Civillisation will not attain perfection until the last stone, from the last church, falls on the last priest.

- Emil Zola

 

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