Friday, 18 May 2007

The Singularity: Follow Up

If you have read my post on The Singularity you would have seen a number of errors in what I said.

I am going to post some comments Dave gave on post.

Well U did ask, & i like thinking about these sorts of things, so here's my input:

>Will somebody who knows what the are talking about >please go through this next bit and correct the errors, >it is just here for the point

> Imagine throwing a ball into the air, accelerating it at 20 m/s^2.
> The starting velocity of the ball will be 0 m/s upward.

No. I think you meant to say the start *velocity* will be 20m/s. The acceleration is *always* 10m/s^2 downward, at any time after the ball has left your hand. It is at that point of leaving your hand that the velocity is 20m/s (which should actually be recorded as -20m/s, since it is in the opposite direction to the acceleration)

> After 1 Second, the ball will be travailing at 20 m/s^2 upward
> but only accelerating upward at 10 m/s^2 due to gravity*.

The velcity will have decreased, cause by the DEcelleration due to gravity. DEceleration of 10m/s/s means after one second, the velocity will be now -10m/s. The acceleration due to gravity, or deceleration due to gravity (numerically the same, only the sign changes with direction) is always 9.8m/s/s on earth.

> After another second the ball will be traveling at 30 m/s^2 upward,
> and the acceleration will be 0. It will no longer be acceleration.

After another second (2 seconds flight time) the velocity will be zero. The accelleration is still 10m/s/s downwards. That is why the ball now starts to fall back to earth - with an initial velocity of zero m/s.

> After the next second, the ball would still be traveling at 30 m/s^2
> upward, but the acceleration is now -10 m/s^2 (or 10 m/s^2 downward).
> After another second, the the ball is still traveling up, at 20 m/s^2, (and > I don't think gravitational acceleration will increase after 10*).

The above 4 lines got me totally confused!
After the ball velocity has reached zero - the top of its flight - it will return to earth. It will reach your hand with the same velocity that it left (20m/s, but this time it is +20m/s, since it is downwards). If you, or the surface of the earth were not present (do this on the edge of a canyon), the ball will continue to accelerate downward at 10m/s/s, its velocity steadily increasing until it reaches something that stops it.

> Okay back to the point. We can see that even though there is force
> in the opposite direction, it is possible for something to keep
> acceleration, although the acceleration will become gradely less

Acceleration is always in the same direction as the force. The acceleration doesn't have to be in the same direction as the velocity: if they are, you get an increase in velocity, if not, you get a decrease in velocity.

**************

I'm open to correction here but I THINK it present they have not discovered enough matter in the universe for it to be an oscillating universe, i.e., it will never cease to expand and wil not contract under gravity.

If there is not enough matter (i.e., mass), then the forces of gravity on all the particles / planets / stars is just not enough to bring the whole expansion to a standstill.

If you throw you ball into the air FAST enough, it will have enough kinetic energy to escape earths gravity altogether, and it will never come down (on earth this 'escape velocity' is 11000 metres per second). Same thing with the big bang - if the initial explosion imparted enough kinetic energy to the matter, there may be insufficient gravity to halt its expansion.

The singularity thing is kinda more complex than just the analogy of a road disappearing to a point (parallax) because it's not just that the things IN the universe were scrunched up into zero physical dimensions, it was the universe itself that had no size - there was no up/down/left/right into which it could expand - space itself expanded and took the matter with it.
Thank you Dave.

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