Miscellaneous Science Questions

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Re: Common Questions - Now With Extra Relativity!

Postby thoughtfully » Sun Mar 29, 2009 8:22 pm UTC

Bright Shadows wrote:Where did the spot of space, matter, and / or time that exploded come from when talking about the big bang?

This is a matter of some speculation. Perhaps it was a collision of branes, a vacuum fluctuation, decay of a false vacuum, the formation of a black hole, or the bounce of a Big Crunch. But it is hard to see how this is even an answerable, well-formed question. How would you know when you had found the answer? What empirical test would you perform?

Maybe when a "complete" theory of the Universe is discovered, there may be an "obvious" answer. But any theory will still be provisional, and subject to future observations. In an important sense, there can never be a theory that is both complete and knowable. Universe as a computer and all that. So perhaps we may one day have a good guess, but I don't think it'll be a testable feature, since Universes lie behind a horizon (or may be in a disconnected spacetime? what does that even mean?), much like black holes.
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Re: Common Questions - Now With Extra Relativity!

Postby Bright Shadows » Sun Mar 29, 2009 8:32 pm UTC

thoughtfully wrote:
Bright Shadows wrote:Where did the spot of space, matter, and / or time that exploded come from when talking about the big bang?

This is a matter of some speculation. Perhaps it was a collision of branes, a vacuum fluctuation, decay of a false vacuum, the formation of a black hole, or the bounce of a Big Crunch. But it is hard to see how this is even an answerable, well-formed question. How would you know when you had found the answer? What empirical test would you perform?

Maybe when a "complete" theory of the Universe is discovered, there will be an "obvious" answer. But any theory will still be provisional, and subject to future observations. In an important sense, there can never be a theory that is both complete and knowable. Universe as a computer and all that. So perhaps we may one day have a good guess, but I don't think it'll be a testable feature, since Universes lie behind a horizon (or may be in a disconnected spacetime? what does that even mean?), much like black holes.


Did not understand:
Branes
Vacuum Fluctuation
False Vacuum
Decay of ^
How a black hole forms from nothing

I get the big crunch idea. The rest are ???.
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Re: Common Questions - Now With Extra Relativity!

Postby thoughtfully » Sun Mar 29, 2009 10:06 pm UTC

I'm not sure I understand branes either. They are a feature of some variants of String Theory. Brian Green's The Elegant Universe is a super book, and a good intro to the subject. The original idea of String Theory was that modeling fundamental particles as zero dimensional points obscures a lot of features and makes some calculations difficult or impossible, so let's bump them up to one dimensional strings. STNG:M-Theory extends this process to objects of arbitrary dimension, which are called "branes".

The black hole wouldn't form from nothing, it forms in a parent (little 'u') universe. Google "fecund universes"

Vacuum fluctuations are also known as "virtual particles". There is a school of thought that the total mass-energy of the Universe is zero, since the gravitational binding energy (binding energy is negative) might exactly balance the mass of all the stuff in the Universe. The length of a virtual particle's life is inverse proportional to its mass. So something that weighs nothing could exist forever. Within the limits of quantum uncertainty.

The false vacuum idea is what all those crackpots who talk about "zero-point energy" are referring to. The problem is, if you were able to create a new vacuum state lower than the current ground state, the new vacuum would expand at the speed of light, releasing the difference in a rather large explosion, completely replacing what came before with something even more bizarre and inexplicable.

If that still confuses you, don't worry. Nobody really knows what's going on. We just make successively better guesses.
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a newbie to special relativity... length contraction.

Postby treolor » Mon Mar 30, 2009 11:33 pm UTC

a man runs at speed u corresponding to gamma=2, carrying a 20m long ladder, into a shed of length 10m, and fits. however from the man's point of view, he encounters a high speed shed of length 5m, which is able to enclose his 20m long ladder. explain.

well, ok.. certainly from an observer's frame i get it - the length of the ladder contracts to 20/2 = 10m since it is moving, so fits in the shed.

similarly from the man's frame the shed is moving, so is of length 10/2 = 5m. but then, how is the 20m ladder going to fit in a 5m shed?? since we know it fitted in the other frame, yes, it must, but... HOW IS A 20m LADDER GOING TO FIT IN A 5m SHED??

confused.

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Re: Common Questions - Now With Extra Relativity!

Postby doogly » Mon Mar 30, 2009 11:58 pm UTC

The way to resolve this is to think about the moment in time when the ladder hits the back of the shed. There is disagreement about simultaneity which when cleared up clears up the rest of the problem (or should at least help a small bit.)
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Re: Common Questions - Now With Extra Relativity!

Postby FayeKane » Tue Mar 31, 2009 6:31 am UTC

Meteorswarm wrote:Matter cannot travel faster than, or even at the speed of light. The reason is that as you approach the speed of light, you gain kinetic energy at a much faster rate than you do at low speeds.

Padwan:

That's not why mass can't travel at c. The reason has to so with what mass is and what light is.

The two directions, time and space, are perpendicular (in four dimensions). Light is energy moving through space at c (but not through time at all). Mass is energy moving through TIME at c. When you accelerate mass, you're rotating it's direction of travel ("momentum vector") away from extent in time to more extent in space. That's why time slows down when you speed up: because you're no longer moving purely in that direction anymore.

If you could rotate your direction of travel 90 degrees, you would be traveling through space with no passage of time at all (like light).

But if you have mass, then by definition, some of your energy (technically, momentum) is pointed into the time direction. And that, again by definition, is not light.

Think of it like this:
If you have mass and continually convert some of it to energy which you use to accelerate what's left, you'd have an object growing smaller and faster, but lighter and so easier to accelerate. C is the limit of that process. The energy required to accelerate any object to c is exactly equal to the mass-energy of the object. To get to c, you have to convert ALL an object's mass to momentum, and they're be no mass left. If there's any mass left, you haven't yet reached c.

Now I'll leave it for YOU to figure out why you still can't get to c by applying extra momentum to the mass BEFORE you start converting it to energy!

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I would be happy to help

Postby FayeKane » Tue Mar 31, 2009 7:14 am UTC

1. How does a photon have momentum?

A photon IS momentum. Momentum through space. Mass is momentum through time.The two directions are perpendicular.

This might help you understand:
Antimatter is moving through time in the opposite direction. When matter touches antimatter, they may look like they're barely moving (through space), but they're both hurtling through time at the speed of light.

When they collide at some particular moment in time, their momentum through time balances, time stops for them, and all that energy is blasted outward at a 90 degree angle from time (through space). Then their energy isn't moving forward OR backward in time; both masses turn into an energy wave expanding outward through space.

That's why, when matter and antimatter touch, all the mass is converted into energy.


2. How does the basic transistor work?

A little guy controls the size of a door. The larger the door, the more other guys can run through it from the kitchen into the dining room. One pin of the transistor the kitchen, one pin is the dining room, and the third pin is the little guy.


3. What is the difference between electrons and photons?

Electrons are pure angular momentum. Photons are pure linear momentum.


4.a How does electrons release energy during collisions.

It releases energy in exactly the same way a rock on the end of a string you're swinging around in a circle gains energy (in a particular direction) when you suddenly release it.

4b. and does the electrons slow down?


Yes. In fact, that's how the dentist makes X-rays. The machine beams electrons at a metal plate which stops them suddenly, and all their energy of motion (I hate to keep using the word "momentum") is released as photons.


5. How does magnitism work?

I know, but I'd rather not say, because my explanation would be phrased such that you'd think I'm just making it up.


6. Is it possible to remove a photon's "field" and can it be used for heating?


You're doing your science homework, aren't you?


7. I was in "an electronic field", for lack of better words, and my finger started to glow, however it was just the tip of my finger, would that be static moving from flesh to fingernail?


I dunno; I wasn't there. Maybe you ate radium. BAD little boy!


8. What is the molecular structure of a super-liquid?


One of the infinite number of things I'm ignorant of is chemistry. Another is everything I understand, like relativity and spacetime. I suspect that I understand the universe approximately as well as my kitty-cat, compared to all there is to know.


9. What is the molecular structure of plasma?


Something got so hot that the electrons were stripped off the atoms and are floating around free (and so are the "nucleuses"). Since both have an electrical charge, plasma pays attention to other things which have a different charge (like the ground beneath your feet). That's why lightning (which is plasma) slams into the earth (though technically, the earth's electricity suddenly jumps up into the sky).

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Re: Common Questions - Now With Extra Relativity!

Postby Klotz » Thu Apr 02, 2009 9:22 pm UTC

How come Cerenkov radiation is blue? If the spectrum is inverse with wavelength, shouldn't the radio components, or at least the red components, be stronger than the blue?

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Re: Common Questions - Now With Extra Relativity!

Postby tdc » Thu Apr 02, 2009 9:46 pm UTC

Klotz wrote:How come Cerenkov radiation is blue? If the spectrum is inverse with wavelength, shouldn't the radio components, or at least the red components, be stronger than the blue?

Red = long wavelength, blue = short wavelength. Hence if the relation is inverse, much more blue than red intensity.

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Re: Common Questions - Now With Extra Relativity!

Postby Klotz » Fri Apr 03, 2009 12:01 am UTC

Yes that make sense. Either I wasn't thinking right, or Cerenkov goes as 1/f, in which case my confusion stands.

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Re: Common Questions - Now With Extra Relativity!

Postby Carnildo » Fri Apr 03, 2009 4:25 am UTC

tdc wrote:
Klotz wrote:How come Cerenkov radiation is blue? If the spectrum is inverse with wavelength, shouldn't the radio components, or at least the red components, be stronger than the blue?

Red = long wavelength, blue = short wavelength. Hence if the relation is inverse, much more blue than red intensity.


Also, it's blue rather than purple because our eyes don't see purple very well. It's the same reason that the sky isn't purple.

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Re: Common Questions

Postby PhaseShifter » Sun Apr 05, 2009 7:46 am UTC

Senefen wrote:
mdyrud wrote:Is it possible to actually reach absolute zero? I could have sworn that somewhere I read that that would violate some law of thermodynamics, but I can't for the life of me figure out where. I am right in believing this, or was I hallucinating?

You're right believing that. 0 Kelvin means stopping the electrons completely, which you just can't do.

If you look over your statistical mechanics, this isn't strictly true.

At T=0, 100% of the molecules (or atoms, or electrons) in a system are in the lowest available energy state. There is no implication of zero kinetic energy, just that it's at an absolute minimum.

That said, there are other reasons you can't reach absolute zero--as you approach absolute zero, thermal conductivity will vanish, so you can't transfer all the heat out of your system in any finite amount of time.

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Re: Common Questions - Now With Extra Relativity!

Postby Ralith The Third » Mon Apr 06, 2009 9:32 pm UTC

-Objects falling in set gravity in a vacuum accelerate at the same speed.


Question- If photons are a particle, and therefore have mass, how do they travel at 1c?
Question- Is there a way to neutralize magnetic fields? So as to have no effect outside of say... a cylinder.
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Re: Common Questions - Now With Extra Relativity!

Postby Sir_Elderberry » Tue Apr 07, 2009 2:32 am UTC

Ralith The Third wrote:Question- If photons are a particle, and therefore have mass, how do they travel at 1c?

They don't have mass. Massless particles exist. They all travel at exactly c.
Is there a way to neutralize magnetic fields? So as to have no effect outside of say... a cylinder.

Superconductors block them, if I remember correctly. I believe you can also set up some other, less cold arrangements that would do similar things, but that's the first thing that came to mind.
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Re: Common Questions - Now With Extra Relativity!

Postby thoughtfully » Tue Apr 07, 2009 4:22 am UTC

Mass is one of the squirmier terms in physics. Particles (like photons) with no rest mass still have energy and momentum. Thus they have mass in the sense that mass and energy are equivalent, and are affected by gravitational fields, but in the normal usage of the term, this doesn't count (it would cause more confusion if it did). Physics is an amazingly tightly integrated self-consistent discipline, we can allow them this one little flaw. Anyway, it's the broken symmetries flaws that give something its personality and uniqueness, right?
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Re: Common Questions - Now With Extra Relativity!

Postby thecommabandit » Wed Apr 08, 2009 5:53 pm UTC

So, I don't know about common questions, but I don't think it's worth making a whole new thread over:

Where does the helium created from a tokamak fusion reactor go? Does it just mix in with the hydrogen plasma? Is it extracted somehow? Can it be?
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Re: Common Questions - Now With Extra Relativity!

Postby Ralith The Third » Wed Apr 08, 2009 8:16 pm UTC

Why, don't you know what they fill balloons with?
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Re: Common Questions - Now With Extra Relativity!

Postby thecommabandit » Wed Apr 08, 2009 9:28 pm UTC

With helium, which they extract from the atmosphere. I'm not asking about the usage of it, I'm asking about the mechanics of it being removed from a reactor.
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Re: Common Questions - Now With Extra Relativity!

Postby thoughtfully » Wed Apr 08, 2009 11:30 pm UTC

This is complete speculation, but the things do need to get refueled when the H runs out. Until then, it all mixes in the plasma, just as in a star's core. Nobody's made a tokamak that actually operates for extended periods yet, so I'm guessing it all gets done when the thing is reset for the next run. Maybe there's a slick zero downtime method, but there's no obvious reason why existing tokamaks would need one.

I don't actually know how long research tokamaks are run typically. I'm just reasoning from generalities.

An interesting question is how the plasma gets in there. Is the magnetic confinement set up first, and plasma injected, or is there cold plasma, confinement applied, and then its heated? If there's injection, then presumably there could be fresh H injected and some of the He enriched stuff could be bled off in sufficiently small amounts so as to cool in a manageable way.
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Re: Common Questions - Now With Extra Relativity!

Postby gmalivuk » Thu Apr 09, 2009 12:46 am UTC

thecommabandit wrote:With helium, which they extract from the atmosphere.

You sure about that?
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Re: Common Questions - Now With Extra Relativity!

Postby Sir_Elderberry » Thu Apr 09, 2009 2:03 am UTC

gmalivuk wrote:
thecommabandit wrote:With helium, which they extract from the atmosphere.

You sure about that?

I'm pretty sure about something else. Most of it comes from natural gas deposits, iirc.
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Re: Common Questions - Now With Extra Relativity!

Postby thecommabandit » Thu Apr 09, 2009 5:05 pm UTC

gmalivuk wrote:
thecommabandit wrote:With helium, which they extract from the atmosphere.

You sure about that?

D'oh. I'm not sure what I was thinking of there, but yeah, it comes from natural gas deposits. Fail.
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Re: Common Questions - Now With Extra Relativity!

Postby Cronqvist » Tue Apr 14, 2009 12:38 am UTC

Hey, uhh...

This is kinda only half-serious,
but a friend and I were talking,
he fancies himself a bit of a cosmologist,
and we were discussing dimensions as measurements of reality,
time being the fourth, etc.,
but the idea of proabability being the fifth came,
it sounded sound.

Could probability be considered the fifth,
that it's only apparent on the quantum scale,
and when a wave function collapses
it is the particle branching
and taking different paths through the fifth dimension?
Conceptually, maybe, at least?

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Re: Common Questions - Now With Extra Relativity!

Postby lordofnarf » Tue Apr 14, 2009 3:25 am UTC

I'm not 100% sure that I'm right, but doesn't relativity state that it is possible for things to travel at or above c so long as they didn't accelerate to c? it's only acceleration that causes dilation and deformation effects, so if something had always existed at or above c, or was caused (by some unknown phenomenon) to spontaneously travel at or above c, that it could theoretically do so?

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Re: Common Questions - Now With Extra Relativity!

Postby doogly » Tue Apr 14, 2009 3:54 am UTC

The 5th dimension thing makes no sense. What do you think dimension means?

Dilation and contraction are special relativistic effects due to relative velocity, not acceleration. Acceleration is a bit trickier to account for, usually you want to whip out a metric to handle this. It's true you can have tachyons traveling faster than c. You can also have lots of things traveling at c, but they must be massless. Light for instance!
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Re: Common Questions - Now With Extra Relativity!

Postby thoughtfully » Tue Apr 14, 2009 3:03 pm UTC

Also, stuff traveling faster than c must have always been so. They have imaginary mass, and have the same restriction on approaching c from the other side as massive particles do. They can, however, increase their velocity without bound (according to Special Relativity). Tachyons, we call them.
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Re: Common Questions - Now With Extra Relativity!

Postby Sir_Elderberry » Tue Apr 14, 2009 11:31 pm UTC

thoughtfully wrote:Also, stuff traveling faster than c must have always been so. They have imaginary mass, and have the same restriction on approaching c from the other side as massive particles do. They can, however, increase their velocity without bound (according to Special Relativity). Tachyons, we call them.

Just so people know, there's no evidence they exist.

Also, they travel backwards in time.
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Re: Common Questions - Now With Extra Relativity!

Postby lordofnarf » Tue Apr 14, 2009 11:45 pm UTC

thoughtfully wrote:Also, stuff traveling faster than c must have always been so. They have imaginary mass, and have the same restriction on approaching c from the other side as massive particles do. They can, however, increase their velocity without bound (according to Special Relativity). Tachyons, we call them.


So is it theoretically possible for something to spontaneously be caused (but not accelerated) to go at above c speeds, and in effect become a tachyon without always having been one?

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Re: Common Questions - Now With Extra Relativity!

Postby doogly » Tue Apr 14, 2009 11:48 pm UTC

They have no evidence you exist either, so I think you should both resolve to be courteous to each other about it.
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Re: Common Questions - Now With Extra Relativity!

Postby Carnildo » Wed Apr 15, 2009 3:24 am UTC

lordofnarf wrote:
thoughtfully wrote:Also, stuff traveling faster than c must have always been so. They have imaginary mass, and have the same restriction on approaching c from the other side as massive particles do. They can, however, increase their velocity without bound (according to Special Relativity). Tachyons, we call them.


So is it theoretically possible for something to spontaneously be caused (but not accelerated) to go at above c speeds, and in effect become a tachyon without always having been one?


No. In order to be able to go faster than c, an object needs to have imaginary rest mass.

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Re: Common Questions - Now With Extra Relativity!

Postby TheCitadel » Mon Apr 20, 2009 11:19 pm UTC

This is not a relevant question, but I'm curious about it. My Biochemistry teacher said hydrocyanic acid smells like almonds. My question is, how do they know? Isn't that thing supposed to kill you right away, even in small quantities? Or is there some reaction that brings out the smell and neutralizes the killing properties, however ridiculous that may sound?
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Re: Common Questions - Now With Extra Relativity!

Postby Ended » Tue Apr 21, 2009 9:34 am UTC

Meteorswarm wrote:Also, pit fruits (like *bitter* almonds, but also peach pits, cherry pits, etc.) actually contain a small amount of cyanide, which is why the smell like it.
Chewing apple pips releases an almond flavour for this reason.
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Re: Common Questions - Now With Extra Relativity!

Postby thecommabandit » Tue Apr 21, 2009 9:31 pm UTC

Ended wrote:
Meteorswarm wrote:Also, pit fruits (like *bitter* almonds, but also peach pits, cherry pits, etc.) actually contain a small amount of cyanide, which is why the smell like it.
Chewing apple pips releases an almond flavour for this reason.

And is also the reason you shouldn't collect apple pips and then eat a large quantity at once. I heard one guy did that and died [citation needed].
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Special relativity discussion/questions

Postby afarnen » Thu Apr 23, 2009 6:08 am UTC

If a body were to start at rest and begin to move at 0.999c relative to an observing body, its time would be slowed and its size would be very small in the perspective of the observing body. The moving body would, of course, notice this same phenomenon of the observing body. Now what happens when the moving body actually reaches the velocity c? Mathematically, its size would be zero and its time would be stopped. What would the observing body actually observe then? Doesn't it follow that this same thing happen to the observing body from the perspective of the moving body, so whatever becomes of one body, becomes of the other (relatively speaking)? it seems to me like the principle of relativity still holds, (however how would one "observe," in a way familiar to us, when one is still in the four dimension)? What about when we cross over to the imaginary numbers, by going faster than c relative to a body? Would that mean that each body would observe the other body in backwards motion while they move forward through time? If backward/forward is relative in this way, does that mean that slower than c/faster than c is also relative? And again, what happens at c?

Of course Einstein said none of this could happen.. but is there empirical data to support the "limiting behavior" idea that we cannot reach c?

oh the mindf*#$ of reading relativity for the first time...

Sorry if this comes across as an uneducated rant. I'm holding myself back a lot, actually. Please discuss.

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Re: Special relativity discussion/questions

Postby seladore » Thu Apr 23, 2009 6:41 am UTC

Yes, there are data that show that a massive body can't reach [imath]c[/imath].

A moving body has momentum

[math]p = \frac{mv}{\sqrt{ 1 - (\frac{v^2}{c^2})}}[/math]

Which is asymptotic approaching the speed of light. What this means is that it would take an infinite amount of energy to accelerate a body of finite mass to the speed of light. Even turning all the matter in the universe into energy, and using it to accelerate the body with 100% efficiency, we'd still only get close to [imath]c[/imath].

The only things that can travel at [imath]c[/imath] are massless particles, such as photons. And yeah, they are weird; time does stop for them.

afarnen wrote:however how would one "observe," in a way familiar to us, when one is still in the four dimension


If you think about it, we are existing in 4-space right now - we move freely in three of the dimensions, and are constrained in the fourth, time-like dimension. Like H G Wells said;

H G Wells wrote:Can an instantaneous cube exist?'

'Don't follow you,' said Filby.

'Can a cube that does not last for any time at all, have a real existence?'

Filby became pensive. 'Clearly,' the Time Traveller proceeded, 'any real body must have extension in four directions: it must have Length, Breadth, Thickness, and - Duration.


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afarnen wrote:What about when we cross over to the imaginary numbers, by going faster than c relative to a body? Would that mean that each body would observe the other body in backwards motion while they move forward through time? If backward/forward is relative in this way, does that mean that slower than c/faster than c is also relative? And again, what happens at c?


You can't go faster than [imath]c[/imath] relative to anything. To add velocities properly, you use the formula

[math]s = \frac{v+u}{1 + (\frac{vu}{c^2})}[/math]

Which again never gives an answer higher than [imath]c[/imath].

If you use the formulae correctly, it is probably easier than you are imagining. No imaginary numbers, nothing going backwards in time. Sure, you have to get used to space and time dimensions being a bit plastic, but once you've got your head round that it's actually OK.


Oh, and don't hold back. As long as it's not covered by the common questions, then feel free to ask anything (unless it's a homework assignment, then people tend to want to give hints rather than full answers).

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Re: Common Questions - Now With Extra Relativity!

Postby afarnen » Fri Apr 24, 2009 1:15 am UTC

Thanks, that all makes sense. I guess I better get back to my holy little relativity book now. On to the general theory!

P.S. And sorry, mods, for forgetting about this thread...

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Re: Common Questions - Now With Extra Relativity!

Postby Zhatt » Fri Apr 24, 2009 8:13 pm UTC

Asking this question I know I'm missing something basic, but I don't know what it is:

A hot air balloon goes up because the hot air is not as dense as the air around it. The cold air wants to sit below the hot air because of weight and gravity, right? Helium is less dense than hot air and therefore wants to rise faster than the cold air as its displaced. Following the concept that the less dense the matter in the balloon, the better, but the lowest density you can have is a vacuum. You can't "fill" a balloon with a vacuum and have it rise. At what point (relative to the balloon and air around it) does a really low density mass just become some loose atoms floating around in a vacuum? :|

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Re: Common Questions - Now With Extra Relativity!

Postby oxoiron » Fri Apr 24, 2009 8:50 pm UTC

Zhatt wrote:You can't "fill" a balloon with a vacuum and have it rise.
You can if you can keep the balloon from collapsing.
At what point (relative to the balloon and air around it) does a really low density mass just become some loose atoms floating around in a vacuum? :|
If there are atoms floating around, it isn't really a vacuum, although many people work with very low pressure setups and call them 'vacuums'. Nobody bothers to correct them, even though we all know that real vacuums don't exist in containers of any reasonable size. I'm surprised that there isn't an agreed upon measurement where we all say, "Fewer than X number of atoms per cubic meter effectively constitutes a vacuum." I suspect this is because it all depends on how stringent your requirements are.
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Re: Common Questions - Now With Extra Relativity!

Postby Zhatt » Fri Apr 24, 2009 10:31 pm UTC

oxoiron wrote:
Zhatt wrote:You can't "fill" a balloon with a vacuum and have it rise.

You can if you can keep the balloon from collapsing.


So, wait. Are you saying that if we had a hypothetical envelope that was light, but strong enough to not buckle under the pressures, you could just pump the air out of the balloon and have the same effect as filling it with helium or the like?

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Re: Common Questions - Now With Extra Relativity!

Postby gmalivuk » Fri Apr 24, 2009 10:52 pm UTC

Yes, that's exactly what would happen. But there's no "just pump the air out" about it, because doing so without it collapsing is really difficult for anything that'd be light enough to work.
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