stupid physics questions

[zip accident]

A lot for the layman to take in here already.

With the limit question, for example -273 degrees kelvin is the lower limit for temperature

No, zero Kelvin is the lower limit for temperature, chosen because you can't get less than zero movement.

[disciple]

Um yeah!

[Darkflame]

And why's the limit 186,000 miles per second, why not 187,000?

Well, it had to be something, so why not that?
Maybe theres other universe's with different constants, or maybe the constants change over time and this is the one we observe at the moment. Theres a lot of unknowens in the "big" big picture.

On the other hand, maybe we should just take C=1 and measure everything else relative to that and the whole of physics/maths might make more sense

[Kelloggs]

I think absolute zero (no, not Absolute_Zero) is another asymptote (and it's -273.15 degrees Celcius, last I looked), but this time one that you can't get to because of... Quantum Mechanics! Well, Heisenberg's Uncertainty Principle, anyway - if you could reduce anything's speed to zero, you'd then know exactly where it is... which you can't know at the same time as knowing that its speed is zero! (Quantum degeneracy, I think.) You'd get things like electrons "crashing" into nuclei, in the classical sense (and Goat-knows-what in the quantum sense).

Also, I just need to correct myself (again) from before; vacuum permeability is defined, not measured (not vacuum permittivity, as I thought).

[pogo]

There is the anthropic principle which says the universe is the way it is, with this number of dimensions, with physical constants as we have, because if the numbers were much different we could not exist. For some numbers if they were much different we could not have suns, planets, galaxies or even atoms and molecules, or the universe would not exist long enough for life as we know it to evolve (many of the heavier elements on Earth had to be formed in dying stars used to make our sun billions of years ago, so the universe must be billions of years older than the Earth).

[Mr Dom]

Short answer:
Stuff can go faster than light, but General Relativity breaks down so can't be used to study things that do (there is a term of 1/(1-v^2/c^2) that appears all over the place that = infinity when v=c, which gives rise to the mass going infinite & stuff.)

Alternate theories (such as Gravitational Gauge Theory) quite happily have things exceeding the speed of light. You can't see em before they hit you tho...


There is more, but I've posted it all before & it's late

[disciple]

And why's the limit 186,000 miles per second, why not 187,000?

Well, it had to be something, so why not that?

But that just avoids the question.

"because it is"

It's like asking why humans generally don't grow above 7ft, or why the clock limit on CPUs tends to be ~4Ghz, they're not just arbitary random figures, there are actual physical reasons for these limits.

[foxyloxy]

Go read Einstein's paper on it. It's pretty simple and explains everything.

[the2bears]

Have we talked about the Quintessence yet?

Bill

[Darkflame]

There is the anthropic principle which says the universe is the way it is, with this number of dimensions, with physical constants as we have, because if the numbers were much different we could not exist. For some numbers if they were much different we could not have suns, planets, galaxies or even atoms and molecules, or the universe would not exist long enough for life as we know it to evolve (many of the heavier elements on Earth had to be formed in dying stars used to make our sun billions of years ago, so the universe must be billions of years older than the Earth).

I always thought that was a bit of a cop-out explanation though. I mean, it depends heavily on the concept of "life as we know it".
I mean, with a few different constants we sure as hell know we couldn't survive, but I think the result would be so radically unpredictable its wrong to state that no intelligent life would be possible. Might even be more common under different conditions, but probably also beyond the ability of our "locally" evolved brains to picture.

But that just avoids the question.

"because it is"

Not at all, because if you read the rest of what I said, every other combination and value might exist as well. Merely not here/now.

Its like saying "isn't it amazing these exact lottery numbers came up". When, in fact, some combinations had to come up, and you could have the exact same reaction whatever numbers came up.

Doesn't mean there has to be a reason why you can't have other numbers and it doesn't, by itself, demand an underlying reason for those particular numbers to come up.

So it isnt so much avoiding the question so much as just saying "there might not be a reason"

It's like asking why humans generally don't grow above 7ft, or why the clock limit on CPUs tends to be ~4Ghz, they're not just arbitary random figures, there are actual physical reasons for these limits.

All of which, when you come down to it, will extrapolate back to the fundamental constants in some ways.

Maybe some of the constants we got fall back to greater underlying rules, but I think your always going to have a "it just is" style answer at some point.

[foxyloxy]

Man, just learn special relativity. It is not hard. General rakes my head (and most other people's - my maths just isn't good enough, and to be fair, wasn't for Einstein, if I remember my history correctly, he had to get massive help learning the insane maths required - curves in nD tensors are just bad and hard), but special is easy.

Yeh you might need to understand the calculus at the end, but it's simple calculus. (last few paragraphs - this stuff is /easy/. A-Level maths easy mostly )

It's just the properties of structure, there is nothing under it. It is. For hells sake, don't get into quantum mechanics till you understand that!

(you will always be wrong).

Read the paper.

If you want to know how the universe operates, even at a reduced model level, words won't cut it. Structure is king.

[Mr Dom]

And why's the limit 186,000 miles per second, why not 187,000?

This is because we have a defined length (a mile), and a defined time (a second). These are entirely human conventions. Then we measure what speed light actually goes at, and that's the number you observe.
Aliens would have their own measures, so to them, light travels at 37,042 quatloobs per flingzub.

Both are the same physical value (although if the aliens lived close to a supermassive black hole, in an area permeated by a high gravitational field, they would measure light as travelling a slower than we measure it out here on a spiral arm, but that's another story to be told another time.)

[Ollie]

Both are the same physical value (although if the aliens lived close to a supermassive black hole, in an area permeated by a high gravitational field, they would measure light as travelling a slower than we measure it out here on a spiral arm, but that's another story to be told another time.)

Erm, no they wouldn't. That's the entire point of relativity. Everyone measures light (in a vacuum) as travelling at the same speed, no matter what their frame of reference.

[Mr Dom]

Both are the same physical value (although if the aliens lived close to a supermassive black hole, in an area permeated by a high gravitational field, they would measure light as travelling a slower than we measure it out here on a spiral arm, but that's another story to be told another time.)

Erm, no they wouldn't. That's the entire point of relativity. Everyone measures light (in a vacuum) as travelling at the same speed, no matter what their frame of reference.

yes, that is the point of relativity.
it is also the point where I think relativity as a mathematical model is rubbish, and alternative models such as Gravitaional gauge theory are more instructive. In this model, the permittivity of free space is not constant, but is proportional to the gravitational field, so light travels slower. This gives effects such as light bending around stars a simpler model that is observably consistent with GR up to the point of an event horizon/speed of light excession whereby gauge theory doesn't go batshit insane with infinities, and still gives sensible real number results.
GR is a model, not the absolute truth.

[gilesgoat]

Both are the same physical value (although if the aliens lived close to a supermassive black hole, in an area permeated by a high gravitational field, they would measure light as travelling a slower than we measure it out here on a spiral arm, but that's another story to be told another time.)

Erm, no they wouldn't. That's the entire point of relativity. Everyone measures light (in a vacuum) as travelling at the same speed, no matter what their frame of reference.

yes, that is the point of relativity.
it is also the point where I think relativity as a mathematical model is rubbish, and alternative models such as Gravitaional gauge theory are more instructive. In this model, the permittivity of free space is not constant, but is proportional to the gravitational field, so light travels slower. This gives effects such as light bending around stars a simpler model that is observably consistent with GR up to the point of an event horizon/speed of light excession whereby gauge theory doesn't go batshit insane with infinities, and still gives sensible real number results.
GR is a model, not the absolute truth.

Let's not forget that physics is based on observation and study of real events.

There simply are/can be "lot of things we never observed YET", phisics works as long as there are reptible experiments
that can be done to confirm the theories and/or discoveries of new things that open other possibilities.

Missing those "lot of theories are" yet theories remain until they are proven/disproven by observation.

It would not be suprising at all if sometime we'll discover something else that will turn all into "yes all we knew so far
was kinda correct but was a special case of and/or there are special cases where this do not apply".

All physics always been and will be like that.