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Lazarus and the Gimp
09-03-2006, 23:07:22
Any of the resident Phys-heads want to tackle this?


First my assumptions. If these are wrong the rest is defiantly wrong

According to relativity all points of reference are equally valid.

According to relativity as an object speeds up its mass increases, at the speed of light its mass would be infinite.

Gravity is a function of mass and distance with the formula (mass1*mass2/distance^2)

Definitions. V1 the velocity at which your mass is increased buy a factor of 10.

Take a space ship shaped somewhat like a catamaran. The cross spars between the 2 hulls are capable of taking a compressive force of 9000 nutons, the gravitational pull between the 2 hulls is only 100 nutons (nice safety margin).

The ship accelerates and at some point reaches V1 relative to the planet itís parsing.

An observer on the planet would see a ship moving at V1 thus its mass is 10 times what it was, the compressive force on the supporting spars is 10000 nutons and thay fail.

An observer siting on the ship observes the ship to be stationary, so the support spar holds, and with the planet moving past it at V1, thus the planets mass (and therefore gravity) is increased buy a factor of 10 causing most structures to fail (because nothing is built to stand in a 10 g field).

Can this contradiction be reconciled within relativity?



Needless to say, I'm buggered if I know.

Japher
09-03-2006, 23:22:13
If the mass increases would not the value of the structual support?

Also, another function of relativity is that length also increases. So while it may be getting heavier it also get "longer" or "thiner"

KrazyHorse
09-03-2006, 23:30:31
Answer: there is no contradiction.

a) F = GMm/r^2 only works in the nonrelativistic regime (where velocities are slow)

b) Even if he managed to fix the giant mess he's made by combining mutually exclusive sets of assumptions, forces are transformed by boosts. The fact that I am feeling a force F is a frame-dependent statement.

Needless to say, if you were to do the problem correctly from the two different reference frames (catamaran and planet) it would go something like this:

Guy on catamaran: Doesn't my spaceship look cool? I wonder what the force holding the two halves of my spaceship apart is? (scribble scribble scribble). Ah. There it is. F!

Guy on planet: Hey, look! A spaceship shaped like a catamaran! Hmmm. I wonder what the stress-energy tensor looks like for such a system. (scribble scribble scribble) Hmmm. Interesting! Hmmm. I wonder what the force holding the two halves apart is in my reference frame? (scribble scribble scribble). F prime, you say? Hmm. I wonder what that force transforms to in the catamaran's reference frame? (scribble scribble scribble). Fdouble prime!

F double prime equals F equals the force felt by the spar

KrazyHorse
09-03-2006, 23:31:12
length also increases

Length contracts in the direction of motion, son.

Japher
09-03-2006, 23:33:28
that's what I meant

KrazyHorse
09-03-2006, 23:43:14
increases = contracts?

;)

Japher
10-03-2006, 00:06:51
Increases in shortness

yeah


uh


you'd be surprised how little nonpracticle physics classes us engineers are required to take

all I was doing was pointing out a missing factor

of course, your explination is better

Funko
10-03-2006, 09:17:49
MrG has a massive increase in shortness.

mr_G
10-03-2006, 09:30:34
huh?

hung like a horse maaik hung like a horse.

a shetland pony that is.

Drekkus
10-03-2006, 10:19:31
more like a shitland pony.

Lazarus and the Gimp
10-03-2006, 19:25:38
I posted KH's response, and this is what I got back-


Your point a, I donít see why but I canít disagree.

Your point b how can my remaining assumptions be mutually exclusive and part of the same theory (I drew them from the same theory did I not).

The implication is that the mass of any object is always its rest mass when viewed from its own frame of reference and the only effect of the increased mass is the gravitational force it exerts on objects that are moving relative to it.

Of cause that creates its own set of problems such as loosing the reason why you canít get to the speed of light due to mass change. (as you approach the speed of light your mass increases exponentially there for your harder to accelerate there for you would need exponentially more energy to accelerate. Ultimately infinite energy would be needed to get to the speed of light.) but if your mass is based on your frame of reference your mass hasnít increased and your free to accelerate.

Or is the base statement there a popular misconception.

Immortal Wombat
10-03-2006, 19:30:06
lol Newtonian relativity. What a wonderful demonstration of Kuhnian incommensurability.

How did you come to be arguing physics with a fifteen year old, Laz?

DaShi
10-03-2006, 19:37:43
The universe exists as long as it is in motion. If any part of it were to come to a complete full stop, the entire universe itself would cease to exist.

Lazarus and the Gimp
10-03-2006, 19:41:13
Originally posted by Immortal Wombat
lol Newtonian relativity. What a wonderful demonstration of Kuhnian incommensurability.

How did you come to be arguing physics with a fifteen year old, Laz?

Hell, he knows more about the subject than I do.

KrazyHorse@home
10-03-2006, 19:59:13
The implication is that the mass of any object is always its rest mass when viewed from its own frame of reference

If that frame of reference is inertial (or, in the view of GR, is a free frame) duh.

Of cause that creates its own set of problems such as loosing the reason why you canít get to the speed of light due to mass change. (as you approach the speed of light your mass increases exponentially there for your harder to accelerate there for you would need exponentially more energy to accelerate. Ultimately infinite energy would be needed to get to the speed of light.) but if your mass is based on your frame of reference your mass hasnít increased and your free to accelerate.

:rolleyes:

What, and acceleration is now a Lorentz invariant?

There's a classic problem which involves constant acceleration from the viewpoint of the accelerated party. In an inertial frame their motion asymptotically approaches the speed of light, but never reaches it. The proper time experienced by the accelerated party asymptotically approaches a finite value as coordinate time (time experienced by the inertial observer) goes to infinity...

KrazyHorse@home
10-03-2006, 20:02:26
There are two basic lessons to be learned here:

a) Don't mix and match physical theories.

b) You can't just jump from one reference frame to another without carefully transforming all the quantities you want to compare.

Vincent
10-03-2006, 20:07:17
c) Don't post it here or people will die or boredom

Asher
10-03-2006, 20:16:15
Bill Nye the science guy! BILL! BILL! BILL! BILL! BILL! BILL!

(SCIENCE RULES!!!)

Lazarus and the Gimp
10-03-2006, 20:44:08
The fact that I don't understand any of this doesn't stop it being oddly compelling. They're such pretty words.

King_Ghidra
13-03-2006, 10:53:32
Originally posted by Immortal Wombat
lol Newtonian relativity. What a wonderful demonstration of Kuhnian incommensurability.

ok you win, you made me google kuhnian incommensurability

i should have known i would end up in some wittgensteinian linguisto-semantic nightmare

still 'lol newtonian relativity' indeed

Drekkus
13-03-2006, 11:13:57
lol indeed.

Gary
13-03-2006, 11:45:10
Oh it's not boring. Pretty unintelligable :D but not boring.

But there's a problem with passing on someone else's knowledge to another forum. Since it isn't one's own, it's difficult to rephrase the answers into one's own words. So you're reputation rests entirely on the expert. Bwa hahahahah.

MoSe
13-03-2006, 11:55:31
yeah, you could say you rely on experts exchange!

Lazarus and the Gimp
13-03-2006, 17:31:48
Originally posted by Gary

But there's a problem with passing on someone else's knowledge to another forum. Since it isn't one's own, it's difficult to rephrase the answers into one's own words. So you're reputation rests entirely on the expert.

I'm making it quite clear that I am merely passing on information that I couldn't hope to understand. My reputation as a wide-eyed innocent in the world of fizzix remains unsullied.

KrazyHorse@home
13-03-2006, 17:37:37
Has he given up yet?

Lazarus and the Gimp
13-03-2006, 18:59:10
Sort of.

It was quite funny, because it's a really bitchy forum, and he was being mercilessly hounded by adolescent Slipknot fans who were claiming to be ninjas in quantum physics.

Japher
13-03-2006, 19:10:12
oooooooh, ninjas!

DaShi
13-03-2006, 19:26:01
They flip out and split atoms.

KrazyHorse@home
13-03-2006, 19:32:07
Originally posted by Lazarus and the Gimp
Sort of.

It was quite funny, because it's a really bitchy forum, and he was being mercilessly hounded by adolescent Slipknot fans who were claiming to be ninjas in quantum physics.

Ooooh. What's the URL?

Funko
14-03-2006, 09:04:52
Originally posted by Lazarus and the Gimp
Hell, he knows more about the subject than I do.

Yeah, but you know what you don't know.