I have some questions about the behavior of objects in space - NASA-type space. It may be a single question in multiple forms. I'd appreciate comments from knowledgeable people.

1. If an object (unpowered) is moving through space and does not strike or fall into the gravitational pull of another object, will it continue forever at the same speed?

2. If not, why not?

3. Is the universe currently expanding, or contracting? If it is expanding, will its movement end with its parts (stars, planets, asteroids, et c.) maximally dispersed at the end stage (heat death(?)) of entropy?

4. Are the orbits of objects (including planets) in our solar system decaying? That is, are objects in solar orbit slowing down and moving closer to the sun?

Thanks, and please remember that straightforward answers are prohibited on page one.

Treadmills and magnets.

I don't think just any object traveling through space could continue on forever without any interruption at the same speed.

Gravity/Escape velocity for the solar system.

Gravity/Escape velocity for the galaxy.

Wouldn't either of these alter the speed?

Space isn't empty. The density of matter may be quite low, but it isn't zero.
Gravity is everywhere. It may be very very weak but it is there. It's what makes galaxies spin. Gravity waves are detectable, and have been.

Guess I'll see you on page two, then, if this thread even makes it that far.

Until then
1. no
2. because I said so
3. I could tell you but then I'd have to kill you
4. There are no orbits, all objects in the solar system are fixed into a series of crystal spheres rotating about the Earth.

Like the wise man said, space isn't empty.  A traveling object will occasionally hit other things and momentum changes will occur.  The momentum of each colliding object and the collision vectors will cause the momentum changes to happen.  Typically one object will speed up, the other will slow and their direction vectors will change.  

Gravity is everywhere, it acts on objects having mass, even light photons.  So, an objects velocity vector will change over time.  It takes fuel, monitoring, action and money to keep a satellite on station partially because of the effects of very small gravity changes and from things like solar wind.  

Transfer orbits have scheduled mid course corrections because of these effects.  

Deep space is more dynamic than it seems.

Forgot: we look at space and see tranquility and peace.  Nothing could be farther from the truth, space is a place of unimaginable violence.

objects in space are closer than they appear

You know, with the exception of one deadly and unpredictable midget, this girl is the smallest cargo I've ever had to transport, yet by far the most troublesome. Does that seem right to you?

came expecting a firefly thread on the episode "Objects in space"........

disappointed.....

^I also assumed a shiny thread



1. Yes unless acted upon by an outside force not otherwise mentioned
2. n/a
3. Expanding based on observations, yes we think so but over a timeframe so mindboggling it makes distances in space seem easily comprehensible by comparison.
4. Negligibly so currently, planets seem to have orbits stable on the order of billions of years unless something changes (perturbed by impact or massive object, or sun expands)

. . . was a good episode.

Space is expanding as well.  Nothing is sitting still.

Spain will claim anything of value that we find in space

Yes, although even deep space is not perfectly empty. The object will inevitably collide with gas atoms, dust and encounter light pressure from even very distant stars. Those things will all change the object relative motion to whatever frame of reference you choose.



Expanding. Everything is moving away from everything else. Imagine a baloon inflating. Galaxies are all on the surface of the balloon. Gravity causes things to cluster, even galaxies, but in general the big bang was just large enough that gravity is too weak to bring it all back together.



Yes, though because the planets are huge and the various sources of 'drag' are relatively small, they're in no danger of changing orbits meaningfully. Imagine the momentum of something the size of a planet moving at thousands of miles and hour. It's not going to slow down much due to interstellar dust, at least not on the timescale of a stars lifespan.

I know fuckall about astrophysics but my understanding is that most scientists believe the universe is expanding.  They believe this because of the red shift (redshift?) detected in the emissions from other stars.  Everything is scooting along -- heading outward from a common point, including the Milky Way.  Add this to radio "background noise" and a bunch of other shit i dont understand, and you get a pretty convincing argument for the Big Bang Theory.

Im sure there are folks here who actually understand the theories, but I get all my info from Dr. Becky, so who knows.

Objects lose velocity and momentum the moment they enter Uranus.

Everything is moving relative to something else in space. We only measure things based on earth being a fixed point but we are moving also.

As did I; it was an especially good episode.

1. Sort of though since motion is relative and the universe expanding the answer ends up technically a no. Particle density being non-zero also helps to make it a no.
2. See #1
3. Expanding as far as we can make out. Yes but only sorta and it's unclear if there will be a rebound. This time is called thermal death or energy death or heat death but it all means the same thing: where every point of the universe achieves a temperature of absolute zero. It's entirely possible that the universe will continue expanding forever and every particle will be infinitely far from every other particle after an infinite time. That's a little abra cadabra for my tastes though.
4. Creation of gravitational waves consumes energy and so it will eventually case orbital decay but the sun will die long before then and destroy/engulf the inner planets.

Fuck the page-1 prohibition in its ass.

in a Newtonian universe, yes. in a relativistic universe, "forever" and "speed" are relative. speed depends on the observer, so does length (time) of travel, which means forever to some observers and not forever to others.


see above


some think it's contracting. more think it's expanding, they compare the galaxies in it to raisins on a loaf of bread. the end of the universe has been predicted to fizzle out into nothingness due to entropy in 10^77 years.


yes, the orbits had been established long ago by the nebulous raw material that later became planets, so they are very stable. but they are decaying slightly due to relativistic drag. they won't change muich at all before the sun dies out and burns up the planets so there's not anything to worry about there.

It's a Space peanut.

I am not waiting for page two.  Why, because you said to wait until page two...  LOL

See above in your quote.

Please elaborate, as I have a pretty vivid imagination, and can imagine quite a lot of violence.

Space is not empty, so any object out there at any given time is being affected.

Ok... excepting the hydrogen and any helium or lithium in your body, every other atom was formed in a star and then ejected across unfathomable distance across the universe when the star exploded. Essentially everything about the universe outside of our little pocket of habitability we call the Earth is 100% always lethal. If you were exposed to the radiation in space for very long you'd get so much cancer the cancer would get cancer. If that's not enough for you....

Ever hear of a quasar? This is where a galaxy shoots at whatever happens to be around to be shot at. Galaxy shoots at you, pew pew pew.

I thought this was going to be about the Firefly episode

Why, did space run out of chicken?

Am I a lion?

I thought gravity didn't exist, just bendy space time and everything is moving in a straight line, from a certain point of view.

Gravity is always there. We, on Earth, are influenced by the gravity of stars in the Andromeda galaxy... Their influence might be immeasurably small, but it's there. and when you add up all the things in the Andromeda galaxy, well there is a reason why our two galaxies are set to merge in the far future. Gravity fall off with the inverse square law. So that when you double your distance from the center of the object (without going under the surface) you decrease the gravity by a factor of 4. That means at 4,000 miles above earths surface gravity is about 25% of what it is on the surface (which is about 4,000 miles from the center, a bit less I know, I'm rounding things off.) Double that distance from the center again to 16,000 from the center, or 12,000 from the surface and gravity is 1/16th what it is at the surface.

And it also works the other way. In real life Earths gravity comes from every bit of matter on Earth, but you can treat it mathematically as if it comes from a point in the center of the Earth. (There is a bit of a discrepancy here because the Earth's core is so much more massive than the crust and mantle due to all that iron. Real life often throws monkey wrenches into mathematical models.) So, if you squeezed earth down to half it's diameter then the surface gravity would be 4 times what it is now. Cut that distance in half again and you are at 16 times, half again and gravity is 64 times as strong at the surface... However, if you did this gravity where we are now, 4,000 miles from the center of the earth, would remain exactly what it is now.

That's how black holes work incidentally. If some force squeezed the sun down to black hole size then Earth's orbit would not change one bit. Solar gravity where we are would be the same as it is now.

Anyway, everything in space keeps it's current momentum as modified by the collective gravitational fields of everything in the universe, at least until some outside force acts on it. It might help to understand that movement can only be measured relative to some other object, there are no absolute spatial coordinates we can use to measure something's speed. So objects in space are sort of standing still in a sense with everything else in the universe moving around them. Since space is not empty anything in space will get hit by other objects, even if they are atom sized objects, and the momentum of those atoms will be added to the momentum of the object in space. That could cause a significant change in velocity over the course of enough time... That's how solar sails work, or how they are supposed to work in any case.

Orbits do change over time for a variety of reasons. For example our Moon causes tides on Earth. These tides slow down Earth's rotation by a small amount each year. But what happens to that angular momentum? It gets transferred to the Moon which causes the Moon to move away from Earth. Eventually the Moon will move far enough away that it will break free from Earth's orbit and start orbiting the Sun, independently from Earth... but in essentially the same orbit. Yea, I don't expect that one to end well.

Well, to be fair, it ran out of crab legs first. The chicken was meant to salve the butthurt from the running out of crab legs but you know how those customers get when they can't get they crab and chicken buffet.

If the theory of an expansionist galaxy is real then it probably continues right up until the speed of light.

After that, I think even the Big Brains here would be speculating

brrrrt. Incorrect. Assuming that the light horizon exists already which evidence is good enough to just grant as likely, even an object that was not in motion relative to anything within light years of itself would appear to be moving faster than the speed of light from some point of view in the universe as long as it was sufficiently far away. From a big enough distance you don't even have to be in real motion in your own frame of reference to be going faster than the speed of light from another frame of reference. There is no limit on relative speed, not even the speed of light. You are free to hurl the chairs around now. The speed of light limitation is applicable to motion from the moving body's own frame of reference, not necessarily the frame of reference of a remote observer.

1. An object in motion stays in motion, unless acted upon by another force. So yes - absent any other interaction, an object moving will continue moving forever.

2. See 1.

3. We don’t know for sure. Current consensus is that the speed at which the Universe is expanding is enough to overcome gravitational attraction, which means we’ll end up with a “Big Freeze” - i.e., the heat death of the Universe. If we’re wrong, and gravitational force is strong enough to eventually overcome the speed of expansion, we’ll eventually end up in a “Big Crunch”.

4. In practice, no orbit is 100% stable, because other objects interact with it. On timescales that matter to humanity, the orbits of the planets are static.

Are you reading a book about or taking a course in astronomy or cosmology?

What is "NASA-type space"?  Do they have their own type?

In your mind, is "strike" different than "struck by"?  Over time, even galaxies collide.  What is this object to which you refer - quark, baryon, atom, dust, rock, asteroid, planet, star, black hole?

Current theory has the universe ending cold and absolutely dark.  Of course, when you know nothing about the dark matter & energy comprising 90% of the universe, it is more than a little difficult to know, with any certainty, how everything will work out.  

Uranus is an object in space

Man is stronger by far than woman, yet only woman can create a child. Does that seem right to you?

Little man loved fire.

Please note that I am not educated in this field however read and watched a lot on the Internet and in print.
And I am currently drinking Captain Morgan 100 proof with RootBeer.

Did someone say satellites?

There's a few up there.
https://geoxc-apps2.bd.esri.com/Visualization/sat2/index.html

Eventually it will all go dark and cold and none of this will matter

At some point someone/thing will witness the last star dying

Worried that the trajectory of 99942 Apophis could change? It is supposed to arrive on Friday the 13th. What could possibly happen?

https://www.forbes.com/sites/jamiecartereurope/2022/04/12/exactly-7-years-from-today-a-massive-asteroid-will-get-closer-to-earth-than-some-of-our-satellites-should-nasa-visit-it/?sh=3457928f40f6

So...
Not a firefly thread?

1.  yes...

2. But... no... since Gravity acts over a very long distance.  The Moon is in Earth's gravity well... The Earth is in the Moons Gravity well.  They're both in the Sun's gravity well... and also perturbed by the gravity wells of the other planets.  The gravity from nearby stars in our Galaxy effect us.  The gravity from the Black hole at the center of the galaxy effects us.  The gravity of the other galaxies effects us.

so there is No place that is not being pulled on by the gravity of some other object.  Orbits happen because objects are being pulled on by gravity.

3. The universe is Expanding and doing so at an ever increasing rate. It is currently not known if it will stop or reverse or continue until all matter is ripped so far apart it can't exist as matter any more.

4. Yes and no.  The orbits are changing.  The Moon for instance is slowly Leaving Earth.  It gets further and further away as time goes on.  But last I checked the Sun will expand into a Red giant and Consume the Earth and Moon before the Moon can leave the Earth.  There's a small chance the expansion will kick the Earth and Moon out instead of being consumed but Mercury and Venus are toast... and the Earth's oceans would be boiled away in any case.

1. Yes.

2. See 1. Objects in motion stay in motion unless acted on by an external force.

3. Don’t know.

4. Also don’t know.

Space is ruined by Star Trek wokeness.

Stick to reruns of Sea Hunt, with Lloyd Bridges—not his panzy-assed manlet children, because there’s no wokeness in 1958 SCUBA.

What did he do?

That is a damn good rule since I don't have any straightforward answers anyway.

This is exactly what I hoped this thread is about. At least someone understands.

Same here. Where's Jubal Early when you need him?