# Is it possible for a spacecraft to be too far from earth to return at any speed ?

Mainly because the universe would keep expanding too fast to return?

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• 2 months ago

I have used simulations to explore this topic,

If I placed a tennis ball somewhere 5 galaxies away, and a tennis ball at our current location on earth, given enough time due to the gravitational forces acting over great distances the balls will collide.

F = GM1M2/r^2

above is newton's gravitational equation

You can tell that as distance between balls r, increases Force decreases greatly. But it will never be 0.

This is assuming that there are no entities in space that interfere along the distance r (such as black holes) and that Newton's equation works for the entire span of the universe.

If however there are interfering entities (which there are due to Hubble's constant) and/or Newton's laws do not apply to all parts of the universe, then with current knowledge on space we cannot answer that question. Any answer made will be a theory.

-Vashi

• wereq
Lv 4
2 months ago

Yeah, the problem is getting the spacecraft to that point.

• 2 months ago

Yes it is. There is a certain distance beyond which nothing can ever reach earth, not even light. It is possible for a craft to get that far away by going very close to the speed of light. But it could never get back or send a signal back to earth, as long as space continues to expand. This is an event horizon, similar to an event horizon in a black hole.

• 2 months ago

The idea of the curvature of space suggests that travel in any direction should eventually return you to your point of origin.

• 2 months ago

It's called the cosmological horizon.

• Dixon
Lv 7
2 months ago

Yes, exactly that. If two locations are so far apart that the hubble constant makes them recede from each other at greater than the speed of light, you could never travel from one location to the other because new space is turning up faster than you can travel through it.

Having said that, in your scenario where you start on Earth and wish to return; it would have to be one helluva journey to get that far away.

• 2 months ago

Does "any speed" include  faster than light ,and does the expansion rate still follow the Hubble law beyond the horizon ?

• 2 months ago

If it is beyond the cosmic horizon, then it will not be able to come back. Because then the expansion rate is more than speed of light.

• Jim
Lv 7
2 months ago

Not normally, but if you include extreme distances then yes, you would actually be traveling faster than the speed of light.

https://wtamu.edu/~cbaird/sq/2014/08/29/will-the-n...