Physics Questions

[Kurt_]

1)
a) If we are accelerating due to the expansion of the universe, why don't we feel it?
b) Same thing for the orbit around the Sun.
c) Same thing for the rotation of the Earth.

2) THEORETICALLY (I know you'd disintegrate due to air friction and all that), if you are in an object traveling at 1 km slower than the speed of light, and you walk/run forwards, what happens? Are you ABLE to walk forwards? It's impossible to travel the speed of light, but is it relative to anything?

3) What happens if you were to sit at the center of the universe? Would you be torn apart by the expansion of the universe (since it expands in all directions)?

4) (Kind of wishful thinking) Do you think that the center of our universe and it's expansion is due to the linking between the center of our universe and the center of another universe in which the other universe is shrinking, pouring matter into ours, fueling our expansion?

[vskid]

1)
a) If we are accelerating due to the expansion of the universe, why don't we feel it?
b) Same thing for the orbit around the Sun.
c) Same thing for the rotation of the Earth.

You only feel acceleration. As we orbit and rotate, its at an almost constant speed. As for the expanding universe, if its accelerating, maybe its too slow for us to feel (or the earth's gravity makes up for it), or its expanding at a constant rate now.
And for number 2, it would be even cooler to fire a gun at that speed, because a bullet can go a lot faster than a human can run. Maybe you'd vaporize if you tried running...

[Triton]

http://en.wikipedia.org/wiki/Metric_expansion_of_space

[gannon]

If we stopped rotating you'd never feel it anyways...you'd get smashed into an object and die

[vskid]

If we stopped rotating you'd never feel it anyways...you'd get smashed into an object and die

lol, it took me a second to figure that out. Go into a wall at approximately 1000 MPH, that'd suck if you survived (powdered bones, flesh turned into mush, etc.). That is assuming your house can withstand the deceleration long enough for you to hit it.

[jperryss]

2) THEORETICALLY (I know you'd disintegrate due to air friction and all that), if you are in an object traveling at 1 km slower than the speed of light, and you walk/run forwards, what happens? Are you ABLE to walk forwards? It's impossible to travel the speed of light, but is it relative to anything?

From the Straight Dope:
"You probably have the idea that if you are standing in a bus moving at speed u, and you walk forward at speed v, your total forward speed w is expressed by the straightforward sum u + v. Alas, this is a cruel illusion.

In reality, what we might call "addition of velocities" is governed by the awe-inspiring equation

w = (u + v)/(1 + uv/c^2)

where c^2 is the speed of light squared..."

http://www.straightdope.com/classics/a2_095.html

[Gamelver]

for the speed of light question: as far as we know, nothing can go past the speed of light. Therefore, if you were to shoot a gun travelling at very close to the speed of light and shot a gun, it's impossible for the bullet to get past the speed of light.

If you were at the center of the universe (speculation here) I think you wouldn't feel anything, as it's just "space" that's expanding. Everything would simply move away from you at the same speed.

for you fourth question:...who the f*** knows ?

[Rekarp]

1)
a) If we are accelerating due to the expansion of the universe, why don't we feel it?
b) Same thing for the orbit around the Sun.
c) Same thing for the rotation of the Earth.

1a. The Universe is probably not accelerating and is moving at a constant velocity or the rate of acceleration is so slow that we do not notice it.

1b. Now orbiting around the sun is a little bit more difficult because we are experiencing a centrifugal force (at least the Earth is). I would assume that the earths own gravity would be a stronger force and kinda override it.

1c. The Earth is rotating at some what of a constant rotation which wold mean no acceleration.

Now think about this. If the Earth stopped rotating we would experience more force from the Earth due to the loss of centrifugal force. This probably wouldn't be that much force but its something to think about.

2) THEORETICALLY (I know you'd disintegrate due to air friction and all that), if you are in an object traveling at 1 km slower than the speed of light, and you walk/run forwards, what happens? Are you ABLE to walk forwards? It's impossible to travel the speed of light, but is it relative to anything?

Well if you where in space you would not have to worry about air friction. I am pretty sure modern science has not answered this yet but it seems plausible. Take for the example the episode of Futurama where Bender gets fired out of a torpedo tube at the ship's maximum velocity. If a ship was going the speed of light and fired a projectile would the fabric of time and space unravel and implode the Universe? Dunno. I will ask my Physics Prof. and see what he says.

3) What happens if you were to sit at the center of the universe? Would you be torn apart by the expansion of the universe (since it expands in all directions)?

I would assume you would just sit there. Yes, the Universe is expanding but thats because of the big bang that happened which gave all the matter in the Universe the momentum to continue to expand. Theres a theory out there that some time (gizzilion years or something like that ) that the momentum from the big bang will run out and the gravity from the galaxies will pull the Universe back together in a big crunch.

4) (Kind of wishful thinking) Do you think that the center of our universe and it's expansion is due to the linking between the center of our universe and the center of another universe in which the other universe is shrinking, pouring matter into ours, fueling our expansion?

Well since most of the Universe is a Vacuum, I would think that its just more vacuum. But, a more important question is what is our Universe expanding into?

/edit : That Straight Dope guy has it right about if you where going near the speed of light. But what if you where traveling at the speed of light or more importantly what if you are light and experience a black hole.

[Gamelver]

The universe isn't really expanding "into" anything, as far as we know. Think of it like dots on a balloon, with the surface of the balloon being our universe and the dots as galaxies. When you blow the balloon up (simulating the expansion of the universe) the dots move farther away. Essentially, space (the membrane of the balloon/universe ) is being "stretched".

[limpport]

3) What happens if you were to sit at the center of the universe? Would you be torn apart by the expansion of the universe (since it expands in all directions)?

That also means that it would expand back on itself. Logicaly, the expansion would be in the shape of a sphere. Now imagine every point on the sphere (basicly the whole thing) acting as the center of another sphere, and so on.

[jperryss]

I enjoy threads like this one, and actually sorta miss studying this stuff in high school. I hope no one screws up and gets it locked.

1c. The Earth is rotating at some what of a constant rotation which wold mean no acceleration.

Yes and no. The Earth is rotating at a constant speed, but everything on the surface (and technically everything that's not exactly in the exact center of the Earth) is feeling a constant centripetal force from the spinning planet. Ever see how a dragster or a funny car's tires get all tall and skinny when they start spinning off the line? Same thing.

My guess is that either a) the centripetal force is too minor for us to feel, or b) the Earth's gravity cancels it out.

[Kurt_]

Many of you are confused as to what acceleration is. Acceleration IS the change in speed, but it can also be the change in a number of other variables, one such being DIRECTION. This was one of the major problems with the model of the atom. An orbiting electron would lose energy (due to acceleation) and collapse into the nucleus. But that didn't happen. Ever.

And Limpport clearly didn't read his PopSci. Remember that Megapixels anyone? The nebula or galaxy or supernova or something that was expanding abnormally, compared to the previously believed spherical expansion?

[limpport]

And Limpport clearly didn't read his PopSci. Remember that Megapixels anyone? The nebula or galaxy or supernova or something that was expanding abnormally, compared to the previously believed spherical expansion?

Nope!

[teraflop122]

(1a) The acceleration is too subtle to feel at the human scale.
(1b) The acceleration is too subtle to feel at the human scale.
(1c) We do feel it- we are all slightly lighter because of it. Stop our rotation, and the change in weight would probably be noticeable or measurable.

(2)You become more massive as you travel faster. The energy needed to accelerate increases with mass. Objects travelling at the speed of light have infinite mass. Accelerating to the speed of light would require infinite energy. I know some people are strong, but last time I checked no one here has infinite strength.

what if you are light and experience a black hole.

One of three things: your path is bent as you pass; you go into orbit; you fall in.

If a ship was going the speed of light and fired a projectile

The ship would need infinite energy to fire a projectile = impossible.

(3) The universe does not have a "center." Everything is moving away from everything else. From my perspective, I am sitting in the center of expansion. From your perspective, you are sitting in the center of expansion. From an alien's perspective, he/she/it is sitting in the center of expansion.

(4) 1st, there is no "center." 2nd, current theories state that the total quantity of matter in the universe is fixed.

However, there ARE some forces thought to be remnants of forces in another universe. Some versions of String Theory and M Theory allow for Gravity, an extremely weak force, to be the shadow of a much stronger force of gravity in another universe. You could then conjecture that Electromagnetism, an extremely strong fundamental force, exists as a very weak force in another dimension.

[Kurt_]

The universe does not have a "center." Everything is moving away from everything else.

If there is no center, how does EVERYTHING move away from EVERYTHING else? If there wasn't a center that would be impossible. At least 1 particle would be moving towards another, in regards to the expansion of the universe.