h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Shouldn't footnote 1 read "...186 thousand miles per second"?

Of course it should.

RhoMuNuQ

Fixed!

...
*prepares for rant*
*looks at watch*
*decides not to rant too much*
black holes do not work for time travel due to a fundamental flaw in the way we think of the abstract concept of spacetime!
...
*thinks*not enough time to explain, must shorten
gravity is the result of the universe moving "up" in the time direction
that is y it is always drawn like a stretchy grid
the more mass u have, the more inertia u have and the slower time is fro u bcuz u dun wanna accelerate up in the time direction
>8^B

I don't understand. what do you mean by time is moving up in the y direction?

no
not the y direction
the t direction
the universe is moving "up" (as in positive) in the time direction
xyzt
...
sorta
i have more time now but i am sleepy
keep asking specific questions and i'll try to give u better answers
>8^B

History, paragraph 2 - "Michell also stated that..." In line 4 "...If a star existed with a greater circumference than this critical circumference, no light would be able to escape..."

I think it should be lesser circumference, unless of course you mean the circumference of the original star and not the circumference of the dark star.

Regards,

yeah i noticed that too but forgot in leiu of a rant that was slightly more pressing according to the voices
>8^B

according to quantum there should be time reversal symmetry. So why does it matter if time is becoming more positive or negative?

Why does the motion of time cause spacetime to be drawn like "a stretchy grid"? Those two are obviously connected.

because of inertia
when they (scientists limited to 3 dimensions) draw the stretchy grid, down refers to it being pulled towards t0
>8^B

First off: you never answered my question of my it matters if time is going positive or negative (time-reversal symmetry)

Second, saying "because of inertia" doesn't answer either question in a meaningful way. You might as well have said "because of socks". It would have the same amount of meaning.

where did the stetchy grid come from?

First off: you never answered my question of why it matters if time is going positive or negative (time-reversal symmetry)

Second, saying "because of inertia" doesn't answer either question in a meaningful way. You might as well have said "because of socks". It would have the same amount of meaning.

where did the stetchy grid come from?

the "stretchy grid" is what they always use to show how matter distorts spacetime
i suppose it does not matter which direction in the time axis we are moving, just that it is away from zero
for once i am happy to explain something, because i think you are smart enough to either understand what i am saying or to show me where i am incorrect
i also like how you are asking questions instead of telling me i am flat wrong
nice open mind you have there
>8^B

now take my two previous posts and put them together
all matter has a velocity pointing "up" (it could be down, all i mean is we r moving away from the origin: t0)
we are also accelerating "down" (towards t0)
and what is acceleration times mass?
force!
aka gravity
hence, the particles look like they are resting on a stretchy grid and pulling it "down"
i have a question about the up/down thingy
is that only because most dimensions are lines and time is a ray?
>8^B

Okay, I'm trying to understand, but I'm not sure if I'm getting anywhere. Thanks for explaining. You seem to be saying that the entire universe is moving, or that all the matter in the universe is moving, which I don't understand. If everything is moving, that means it is moving with respect to something else, which means that the definition of the universe is not everything (b/c there is something else out there that it is moving with respect to).

I don't like the analogy of the stretchy sheet, b/c it requires the classical newtonian force of gravity to create it - if you were in free fall with the sheet and the ball, you wouldn't get the right effect. The ball wouldn't weigh down and distort the sheet. Further, even if you forcibly dimpled the sheet, you couldn't roll a ball along the sheet. I guess you'd need a metal sheet and a magnetic ball to hold it onto the sheet, but then you've added a whole other set of forces.

Let me run this by you, to see if I understand. An object has a certain trajectory in "free" space. It comes near the earth, where space-time is curved. The object, because of inertia, wants to keep going straight, but is forced to curve along the path given by the structure of space-time. So, in this way, inertia is a key component of gravity, the other key component being the curvature of space-time.

Is this right?

sort of
what we (as particles) are moving relative to is our past selves
but each particle moves into the future at a rate depending on the distortion of the surrounding spacetime (and its own mass if we r assuming that the particles are not zero-mass or constant-mass)
and because each particle is moving at a different rate, they distort spacetime
that is, the slower particles are pulling down on spacetime, because each particle pulls on each other particles
the grid itself (stretchy sheet) does not exist
wait
that goes back to gravity
darn
well
i guess what i am saying (now) is that the stretchy grid does not exist and it is only a metaphor used to show how particles pull on each other in four (or more) dimensions, not three (or more) as we previously thought
basically now i say gravity is a property of spacetime, not a property of space
but that hints that objects are not only pulled toward each other, but also to the trails that the object has left in the past and the ones in the future
that means that when the universe started, all the particles were being pulled towards their futures and each other's futures
that also means there is a time equilibrium point
before this point, all matter is accelerating away from the beginning of time, and after it all matter is accelerating towards the beginning of time
hmm
don't try to follow, i have given up following it and it is within my own brain
and outsider cannot comprehend without a vast background in the field
sorry i got u interested
>8^B

That's okay, I'm still working. I'll keep up with my own reading - I'm working through differential geometry now.

hmm
i was rereading my post and a thought jumped out at me
spacetime is a four (or more) dimensional one of those vector fields
like the ones that u drop a dot on a point and it follows the arrows
>8^B

well, I can picture a vector field in 2 and maybe 3 D, so by extension I understand the concept of one in 4D.

So inertia says you travel in the "same direction", but spacetime tells you that the direction is curved near heavy objects. In this case, what does inertia have to do with gravity? Inertia is still just inertia, and gravity is now something different then before, but nonetheless, something that perturbs inertial movement.

dave

now that i have confused myself i do not have an answer
i'll try, tho
hold on
*long pause*
ah yes
in my previous model, inertia was there to resist the pull of time
that is, the pull on the other particles
i think
hmm
>8^B