# What would happen if I stopped?

I mean a complete stop.

Suppose I’m sitting in some sort of craft that would survive this, let’s say the craft is in NYC’s Central Park and that I either pass through objects or just plain miss them.

How long will I:

Still be in the earth’s atmosphere?

Still be in the solar system?

Still be in the Galaxy?
How much of a speed change would be involved in coming to a complete dead stop relative to the universe?

There’s no such thing as an absolute dead stop. All motion is relative.

You need to pick something to have a speed relative to, your best bet for this example would be what’s usually referred to as the fixed starts. This would give you a lot of component velocities (sorry I’m not an astronomer I don’t know what the speeds are)

Earth’s rotation

Earths orbit round the sun

Sun’s motion through the galaxy

The galaxy’s motion relative the the local group (or whatever it’s called)

and so on…

I guess that the first two would be swamped by the later ones. C’mon guys someone out there knows. Lets give Zebra the dope.

Well, as in all deep and meaningful questions we must ponder, I turn to Monty Python. The Galaxy song.

I’ll let you do the math.

As Small Clanger said, “You need to pick something to have a speed relative to.”
The best choice for this would be the cosmic microwave background. As these COBE and WMAP pictures show, the earth’s velocity shows up as red or blue-shifting of the 2.7°K radiation. Too bad I can’t find a number to stick on that speed this morning .

If relative to the Milkyway, I came to a complete stop etc…

Okay, I had some time, so some math was done.

Just remember that you’re standing on a planet that’s evolving
And revolving at nine hundred miles an hour, 900 mph
That’s orbiting at nineteen miles a second, so it’s reckoned,19 mps = 68,400. So we get 900 + 68,400 = 69,300 mph
A sun that is the source of all our power.
The sun and you and me and all the stars that we can see
Are moving at a million miles a day. A million miles a day i approx 41,667 mph. So 69,300 + 41,667 = 110,967 mph.
In an outer spiral arm, at forty thousand miles an hour, 110,967 + 40,000 = 150,967
Of the galaxy we call the ‘Milky Way’

I’ve asked physisists that I’ve met how accurate The Galaxy song was, and they’ve tended to be of the opinion that Idle did a pretty good job. Sorely lacking is expansion speed, but that really gets to be an Appelatian dating pool (it’s all relative).

But these are angular velocities with not only speed but (changing) direction, in 3 dimensions. So we can’t stack them on top of one another in a direct line.

In short, there is a strong likelyhood that one might head through the center of the earth into space as likely as head off at some tangent or some other ridiculous angle. Either way, I recommend seatbelts and a good lid on your coffee cup.

Here you go. We’re moving at 389 km/sec with respect to the cosmic microwave background, which is (as Squink said) the best choice for a “fixed background.” I would guess that these values are corrected to cancel out the satellite’s motion around the earth and the earth’s motion around the sun, though (since these measurements were taken over a period of years.) So you’d have to add back in the Earth’s rotation and revolution. I’ll leave those as an exercise for the reader.