# QuestionConstellations/ Space travel

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#### Pogo

Wait! What? OK, galaxies are thousands, if not millions of light years apart. Stars are typically a few light years apart. Two ships at almost c to meet in a week would have left planets two light weeks apart. Stars that close are either part of a binary system, or they are really disrupting one another’s Oort clouds, and even their Kuiper belts. Heaven help the small planets.

But, anyway, a week’s travel would not be enough time to accelerate to 0.99c within that week.

But, even if you started sufficiently far apart and have a really long time to try this, it would take such a humongous rocket and prodigious amount of fuel, that it would be impractical. So, this becomes no more than a thought experiment, and I don’t know the answer.

#### Helio

I understand that we are travelling relative to CMBR.
But I read that there is no absolute velocity in the universe.
Velocity is only relative, thus "Relativity".
And I read that no moving observer using any machine they carry with them can determine their own absolute velocity.
So what gives? Any ideas?
I just noticed this question...

I’m no expert, but as I see it, it helps to separate velocities between speeds through space and speeds due to expansion (co-moving) of space. Imagine giant clocks in every galaxy of equal size and mass. They would all tick at the same rate as the MW clock. The CMB has those same clocks. The light from those galaxies and the CMB travel through space and are redshifted.

An absolute velocity would require an absolute reference point. If the universe had a center, then absolute velocities would exist, but there is no center.

Ironically, however, the speed of light is an absolute, which gave us relativity. This speed is measured to be the same regardless of one’s inertial frame. This reveals that other moving reference frames will present to us their time dilation, and they say the same about our clock rates.

#### Atlan0001

I just noticed this question...

I’m no expert, but as I see it, it helps to separate velocities between speeds through space and speeds due to expansion (co-moving) of space. Imagine giant clocks in every galaxy of equal size and mass. They would all tick at the same rate as the MW clock. The CMB has those same clocks. The light from those galaxies and the CMB travel through space and are redshifted.

An absolute velocity would require an absolute reference point. If the universe had a center, then absolute velocities would exist, but there is no center.

Ironically, however, the speed of light is an absolute, which gave us relativity. This speed is measured to be the same regardless of one’s inertial frame. This reveals that other moving reference frames will present to us their time dilation, and they say the same about our clock rates.
Yep! The speed of light is the absolute of momentum. Now what does that mean for position? Would all positioning be a matter of relativity? No absolute of position? I have an absolute answer, but I'm looking for relative opinions.

Shawn.Boike

#### Shawn.Boike

How far can we travel through space, until the constellations are no longer recognizable?
The key is which constellation? Unless you are burning up by a star or being pulled into a black hole. You can see constellations, too many to count

#### pavithra

How far can we travel through space, until the constellations are no longer recognizable?
I think we want to travel the edge of the universe but it is so difficult because this universe expanding faster than light speed

billslugg

#### Atlan0001

I think we want to travel the edge of the universe but it is so difficult because this universe expanding faster than light speed
The traveler under powered, accelerative, flight, local universe-wise, could match the observed acceleration of nonlocal expansion . . . and exceed it locally (achieving point and point, point to point, contraction of the local universe which is exactly what any traveler wants).

No traveler ever closes, really, with the frame infinities of the collapsed constant horizon of c, much less reaching .99c. Not unless the traveler is accelerated to it in the black hole of a Large Hadron Collider-like closed systemic environment by a leveraged external driver. Otherwise, it, the traveler's assumed position and velocity, is nothing more than that light-time history which is relatively observable to any distant observer distant from a traveler (in a future light cone relative to the observer) no longer anywhere near the observed position or velocity. That observer, in reality, has no fishing line tether ruling the traveler's ability to contract space and thus time between point and point, point to point, which is positionally inverted eigenvector(?), or an inverted square matrix(?), and has no local relationship to velocity or the speed of light (which the traveler always traveling a warp space of superficial distances will always measure the speed of light 300,000kps (if not being locally mashed flat, ship and all, by some black hole super-acceleration)).

(I've often imagined the possibility of 32 feet per second per second per second.... which when closed up in horizon would simply mean nothing more than 32 feet may not be an absolute measurement of its own space in the universe at large.)

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#### SomeMumblingBum

Since the Universe, by definition, is everything there is, you cannot be outside of it. Since there is only one Universe, the term "universes" is illogical.
Having said that,
Isaac Asimov once described what he referred to as the Observable Universe. Consider that the Universe as we know it is expanding. Also consider that the further away a give point is, the faster it is moving relative to the observer.

And easy way to demonstrate this is to imagine three points, A, B, and C., in a straight line, equidistant apart. From A to B is 1 billion miles, from B to C is 1 billion miles. Then, from A to C is 2 billion miles. If A is moving away from B at 1000m/s, and B is moving away from C at 1000m/s, then C is moving away from B at 1000m/s,, but moving away from A at 2000m/s. The further away a give point is, the faster it is moving relative to the observer.
At some point distant from the observer, objects are moving at c relative to the observer, and objects more distant are moving at faster than c relative to the observer. Therefore, any object moving at more than c relative to the observer can no longer be seen by the observer because that light can never travel faster than the velocity of that object relative to the observer.

Since the distance between objects in an expanding Universe is proportional to time, due to the speed of light, the further an object is from an observer, the older it is compared to the light that the observer sees from it.

The most distant object we can see will be at the very edge of the Observable Universe. Therefore, since there is no way to tell what is past the edge of the Observable Universe, it is irrelevant to us.
Forgive my remedial question…but if our universe is, indeed, expanding, then it must be then increasing its size/volume. How can our universe get any larger if there is nothing else past the edge of our universe. Surely, as we expand, we must be absorbing whatever else is utilizing the space we have yet to expand to, no? Even if there is nothing else taking up any space beyond our universe, then would it not be correct in thinking of the vast emptiness as an infinite or otherwise area of volume much like our universe, though with nothing (matter of whatever variety) occupying that space? An empty void is still a tangible space that can be realized.

#### billslugg

The Universe expands equally in all directions as seen from every location within it. There is no edge to it. The Universe is a three dimensional analog to the two dimensional expanding surface of a balloon. There is no center to a balloon's surface and it expands equally as seen from every spot on it.

#### arturo.v.dominguez@gmail.

How far can we travel through space, until the constellations are no longer recognizable?
To the far end of the universe which is the linear/90 degree opposite of where you started from. So long as it is at the very least equal distance to where you started from. Of course, that presupposes the constellations are three dimensional non mirror images.

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