[Bored chemist]

This sphere is just one part in the entire Universe that should be bigger than that.

Why?
You are claiming to know about things outside the observable universe.
Have you been there to check?

[Bored chemist]

As you claim that you understand physics, why don't you use this formula to kick out the BBT? Why only Theory D?

BBT explains it by saying that space expands.
You say space does not expand.

That's the difference.
Did you not realise that?

[Bobolink]

It is quite clear to me by now that you are using terms/laws/formulas/theories/hypothesis... only to disqualify other theories.

The way science works is that a hypothesis is presented and the community asks question and challenges the hypothesis to see if it is viable.

Based on your current understanding about relativity, any galaxy in our Universe couldn't move faster than the speed of light.

That is correct, according to relativity nothing can move through space at a speed greater than c.  Which is why I said this is an issue for your idea.  It seems like this is something that should be addressed!

However, our scientists claim that a galaxy at a distance of 13 BLY is actually moving away from us almost the speed of light. Due to the idea that the Universe is isotropic and homogenous, a galaxy at 26 BLY should move away at 2c
We know that our observable universe is 94 BLY. Therefore, a galaxy that is located at the edge in one side, is moving away from the galaxy at the other side at velocity of:
94/13 c = 7.23 c.
Our scientists claim that the entire Universe should be quite bigger than this 94 BY
If we just assume that the entire universe is 130 BLY, than a galaxy that is located at the edge in one side, is moving away from the galaxy at the other side at velocity of 10c.
So, based on the current BBT theory you should know for sure that galaxies are already moving away from each other at a velocity which is much faster than the speed of light.

I wanted to talk about your idea not the BBT.  As you have said the BBT is wrong so there is no reason to bring it into the conversation.

Therefore, I wonder how could you claim that: "the galaxies move faster than c so that would violate relativity." while you know for sure that based on the BBT galaxies are moving away from each other at least 7 times the speed of light?

I do not know that for sure!  Please don't assume you know what I think.

Getting back to your hypothesis, I would like to know how it handles this apparent conflict with relativity.  To my way of thinking there are 3(?) options:
1.  Relativity is wrong.
2.  There is some sort of mechanism in your hypothesis that allows superlumial velocities without violating relativity.
3.  The galaxies only appear to be moving faster than light.

Is one of those correct or is it something else?

[Dave Lev (OP)]

I do not know that for sure!  Please don't assume you know what I think.

So, please look again at my calculation:

our scientists claim that a galaxy at a distance of 13 BLY is actually moving away from us almost the speed of light. Due to the idea that the Universe is isotropic and homogenous, a galaxy at 26 BLY should move away at 2c
We know that our observable universe is 94 BLY. Therefore, a galaxy that is located at the edge in one side, is moving away from the galaxy at the other side at velocity of:
94/13 c = 7.23 c.

Do you agree that the furthest galaxies at our observable universe are moving away from each other faster than the speed of light (7.23c?)?

Getting back to your hypothesis, I would like to know how it handles this apparent conflict with relativity.  To my way of thinking there are 3(?) options:
1.  Relativity is wrong.
2.  There is some sort of mechanism in your hypothesis that allows superlumial velocities without violating relativity.
3.  The galaxy only appear to be moving faster than light.

Well, relativity is relatively.
If you understand theory D, you would see that there is no contradiction.
Let's look at the following example - Rocket over rocket over....rocket.
We know from relativity that:
"Maximum speed is finite: No physical object, message or field line can travel faster than the speed of light"
So, the maximal velocity of a rocket must be finite and significantly less than the speed of light.
However, this is relativity to its base.
Therefore, let's assume that a rocket can travel at 0.01 c.
I hope that you agree that there is no problem with that estimation.
So, let's assume that we fire a rocket (rocket 1) from earth (let's ignore the gravity impact of the earth). This rocket cross the space at 0.01c.
After one day a second rocket (rocket 2) is fired from that rocket 2 also at 0.01c and in the same direction as rocket 1.
In this case, do you agree that the relative velocities are as follow?
Erath to Rocket 1 = 0.01c
Rocket 1 to rocket 2 = 0.01c
Earth to rocket 2 = 0.02c.
Now, if we continue with this process every day than after 10 days:
Earth to rocket 10 = 10 * 0.01 c = 0.1c
With regards to rocket 10.
Let's assume that it can only see rocket 9. In this case, if we were riding on rocket 10 we could think that we are moving at only 0.01c with regards to the space. as rocket 9 is the only relative reference that we have.
If we continue than after 100 days:
Earth to Rocket 100 = 1c
However, again
If rocket 100 can only see rocket 99 it might think that its relative velocity is just 0.01c
If we continue more and more than after 1000 days:
Earth to Rocket 1000 = 10c
Also in this case, rocket 1000 that only see rocket 999 might think that its velocity is only 0.1c
So, Rocket 1000 considers that it is only crossing the space at 0.01 c while relatively to earth it is moving away at 10c.
Do you see any violation in the relativity?

[Bored chemist]

a galaxy at a distance of 13 BLY is actually moving away from us almost the speed of light. Due to the idea that the Universe is isotropic and homogenous, a galaxy at 26 BLY should move away at 2c

That's still wrong.
You can't just add relativistic velocities as if they were apples.

[Bobolink]

Do you agree that the furthest galaxies at our observable universe are moving away from each other faster than the speed of light (7.23c?)?

I want to discuss your hypothesis, no need to go over what the BBT says.

Well, relativity is relatively.
If you understand theory D, you would see that there is no contradiction.
Let's look at the following example - Rocket over rocket over....rocket.
We know from relativity that:
"Maximum speed is finite: No physical object, message or field line can travel faster than the speed of light"
So, the maximal velocity of a rocket must be finite and significantly less than the speed of light.
However, this is relativity to its base.
Therefore, let's assume that a rocket can travel at 0.01 c.
I hope that you agree that there is no problem with that estimation.
So, let's assume that we fire a rocket (rocket 1) from earth (let's ignore the gravity impact of the earth). This rocket cross the space at 0.01c.
After one day a second rocket (rocket 2) is fired from that rocket 2 also at 0.01c and in the same direction as rocket 1.
In this case, do you agree that the relative velocities are as follow?
Erath to Rocket 1 = 0.01c
Rocket 1 to rocket 2 = 0.01c
Earth to rocket 2 = 0.02c.
Now, if we continue with this process every day than after 10 days:
Earth to rocket 10 = 10 * 0.01 c = 0.1c
With regards to rocket 10.
Let's assume that it can only see rocket 9. In this case, if we were riding on rocket 9 we could think that we are moving at only 0.01c with regards to the space. as rocket 9 is the only relative reference that we have.
If we continue than after 100 days:
Earth to Rocket 100 = 1c
However, again
If rocket 100 can only see rocket 99 it might think that its relative velocity is just 0.01c
If we continue more and more than after 1000 days:
Earth to Rocket 1000 = 10c
Also in this case, rocket 1000 that only see rocket 999 might think that its velocity is only 0.1c
So, Rocket 1000 considers that it is only crossing the space at 0.01 c while relatively to earth it is moving away at 10c.
Do you see any violation in the relativity?

Yes, that is a clear violation of the theory of relativity.  According to relativity no mass can travel at the speed of light let alone exceed it.  If laser pulses were sent from earth along side the series of rockets, in this scenario, after rocket 100 the subsequent rockets would pass the laser pulses since they exceed c relative to earth where the laser light is coming from.

So it sounds like choice 1?  If you agree that choice 1 is correct we can move on, if not we can continue with the relativity discussion.

[Dave Lev (OP)]

Yes, that is a clear violation of the theory of relativity.  According to relativity no mass can travel at the speed of light let alone exceed it.  If laser pulses were sent from earth along side the series of rockets, in this scenario, after rocket 100 the subsequent rockets would pass the laser pulses since they exceed c relative to earth where the laser light is coming from.

So it sounds like choice 1?  If you agree that choice 1 is correct we can move on, if not we can continue with the relativity discussion.

Why not?
In the following article it is stated:
https://hypertextbook.com/facts/1999/PatriciaKong.shtml
"Due to relativity, the speed of the Milky Way varies when compared with different objects in space."
So, we can estimate our velocity only by observing different objects in space.
Do we see any fixed reference in the space?
If we can't see any object around us, how could we know our real velocity in space?
Based on this article, only the observable objects in the space could give us an indication about our relative velocity at our current location.
So, if each rocket can only see a nearby rocket, than each one of them could think that its velocity is only 0.01c while as I have proved, the rocket 1000 is moving away from earth at 10c.

[Bored chemist]

In this case, do you agree that the relative velocities are as follow?
Erath to Rocket 1 = 0.01c
Rocket 1 to rocket 2 = 0.01c
Earth to rocket 2 = 0.02c.

No.
Of course I don't agree.

addition.JPG (10.5 kB . 243x89 - viewed 2576 times)

[Bored chemist]

So, if each rocket can only see a nearby rocket, than each one of them could think that its velocity is only 0.01c while as I have proved, the rocket 1000 is moving away from earth at 10c.

No matter how many times you say that, it is still wrong.

[Bobolink]

Why not?

As I pointed out, a laser from earth pointed parallel to the rockets would go slower than the all the rockets after rocket 100.  Do you disagree with that?

In the following article it is stated:
https://hypertextbook.com/facts/1999/PatriciaKong.shtml
"Due to relativity, the speed of the Milky Way varies when compared with different objects in space."
So, we can estimate our velocity only by observing different objects in space.

Correct velocity is relative.  There is no absolute frame of reference.

Do we see any fixed reference in the space?

No.

If we can't see any object around us, how could we know our real velocity in space?

You cannot, it is not even worth asking what is our 'real' velocity.

So, if each rocket can only see a nearby rocket, than each one of them could think that its velocity is only 0.01c while as I have proved, the rocket 1000 is moving away from earth at 10c.

What about the laser light that is moving along side the train of rockets?  The rockets will exceed the speed of that laser light!  That violates relativity.  We can see billions of light years away so we could see all of the rockets from earth anyway (if the telescope was powerful enough).
So it is still looking like number 1 is your answer.

edit to add:  I am not trying to do 'gotcha'.  If you think relativity does not apply in this case, that is certainly an issue that needs to be hashed out at some point, but I have no problem saying ok and moving on.  If you want to continue with the relativity discussion that is fine too.

Additional edit:  Let's make a number 4,
4.  It is not clear how relativity plays out in theory D, this will be more fully investigated at a later date.

[Bored chemist]

So it is still looking like number 1 is your answer.

I don't think he feels that relativity is wrong.
I just don't think he understands what it means.


Anyway, if he's going to say that relativity is wrong, he's going to struggle.
It's probably the best tested idea in the whole of science.
It may be that's why he won't say he disagrees with it.
But the problem is, if it's correct (or even close), then his idea of an infinitely old universe fails.

[Bobolink]

I don't think he feels that relativity is wrong.
I just don't think he understands what it means.


Anyway, if he's going to say that relativity is wrong, he's going to struggle.
It's probably the best tested idea in the whole of science.
It may be that's why he won't say he disagrees with it.
But the problem is, if it's correct (or even close), then his idea of an infinitely old universe fails.

I certainly don't disagree, I am just interested in discussing his idea to see where it leads.

[Dave Lev (OP)]

As I pointed out, a laser from earth pointed parallel to the rockets would go slower than the all the rockets after rocket 100.  Do you disagree with that?

Yes, that is correct

Correct velocity is relative.  There is no absolute frame of reference.

Thanks

Quote from: Dave Lev on Today at 15:46:08
If we can't see any object around us, how could we know our real velocity in space?

You cannot, it is not even worth asking what is our 'real' velocity.

Thanks again

What about the laser light that is moving along side the train of rockets?  The rockets will exceed the speed of that laser light!  That violates relativity. 

No. It doesn't.
We currently see that activity in our real Universe.
I have already offered an example for that.

Quote from: Bobolink on Today at 05:27:20
However, our scientists claim that a galaxy at a distance of 13 BLY is actually moving away from us almost the speed of light. Due to the idea that the Universe is isotropic and homogenous, a galaxy at 26 BLY should move away at 2c
We know that our observable universe is 94 BLY. Therefore, a galaxy that is located at the edge in one side is moving away from the galaxy at the other side at velocity of:
94/13 c = 7.23 c.
Our scientists claim that the entire Universe should be quite bigger than this 94 BY
If we just assume that the entire universe is 130 BLY, than a galaxy that is located at the edge in one side, is moving away from the galaxy at the other side at velocity of 10c.
So, based on the current BBT theory you should know for sure that galaxies are already moving away from each other at a velocity which is much faster than the speed of light.

I wanted to talk about your idea not the BBT.  As you have said the BBT is wrong so there is no reason to bring it into the conversation.

You might think that I focus on BBT, But I want to highlight that even today we know that there are galaxies that are moving away from us a speed which is faster than the speed of light.
I assume that it was very clear also to Bored chemist.
However, if I understand him correctly, he claims that this speed of higher than the speed of light is due to expansion.

BBT explains it by saying that space expands.
You say space does not expand.
That's the difference.
Did you not realise that?

So, as long as galaxies are moving away from each other significantly faster than the speed of light due to the expansion than this is fully ok for Bored chemist.
However, for me - as long as we all agree that galaxies are moving away from each other faster than the speed o light than this is good enough.
So back to your question:

What about the laser light that is moving along side the train of rockets?  The rockets will exceed the speed of that laser light!  That violates relativity.  We can see billions of light years away so we could see all of the rockets from earth anyway (if the telescope was powerful enough).
So it is still looking like number 1 is your answer.

It is clear that at the far end of our visible universe there is a galaxy that is moving away at a speed that is almost the speed of light. We clearly see that galaxy.
If we could stay at that far end galaxy we should clearly see many more galaxies that are located further away and moving away from this galaxy at ultra high velocity.
Therefore, it is clear that behind the furthest galaxy that we can still see, there are more galaxies that are moving away faster than the speed of light that we can't see.
So, if the relativity can accept the idea that galaxies are moving away faster than the speed of light due to expansion, than relativity should except the idea that galaxies are moving away due to Rocket over rocket.
If you think about it, there is almost full similarity between the two ideas.
In the expansion any two nearby points are moving away from each other at a fixed velocity. We call it the expansion rate.
The Rocket over rocket works the same as the expansion.
Any two nearby rockets are moving away from each other at a fixed velocity. So the outcome is identical to the expansion.

Let me offer a better solution.
However, let's start by the following explanation about the expansion:
https://www.space.com/17884-universe-expansion-speed-hubble-constant.html
"thanks to NASA's Spitzer Space Telescope, and it's a doozy. Space itself is pulling apart at the seams, expanding at a rate of 74.3 plus or minus 2.1 kilometers (46.2 plus or minus 1.3 miles) per second per megaparsec (a megaparsec is roughly 3 million light-years)."
so, the expanding rate is about 75 kilometers per second per 3 million light year.
1 Day = 86400 Seconds
So, in one day the expansion rate is
75 x 86,400 = 6,480,000 km
So, Let's assume the Universe is empty
I have unlimited no of rockets over rocket over...rocket.
So I start at a single point in this empty universe. Let's call it A.
I fire 6 rockets at the same moment to all directions (up/down/left right/inwards/outwards
Those rockets should move exactly at the expansion rate.
After one day we will fire 6 rockets from each of those first 6 rockets. So in total we will fire 6^2 = 36 rockets at the second day.
On the 10 day we will fire 6^10 rockets
At the 1000 days = 6^1000.. and so on.
So, if we will continue with this process for 13.8 BY we will get exactly the same impact as the expansion.
Therefore, as Bored chemist had accepted the idea of galaxies that are moving faster than the speed of light due to the expansion, he also should accept the idea of moving faster than a speed of light due to the Rocket over rocket mechanism.
As the expansion doesn't violate the relativity, then also rocket over rocket doesn't violate.

[Bored chemist]

Therefore, as Bored chemist had accepted the idea of galaxies that are moving faster than the speed of light due to the expansion, he also should accept the idea of moving faster than a speed of light due to the Rocket over rocket mechanism.
As the expansion doesn't violate the relativity, then also rocket over rocket doesn't violate.

That's just not true.
And, no matter how many times you say it, it with still not be true.

The fabric of space times is not the same as a rocket.

[Dave Lev (OP)]

That's just not true.
And, no matter how many times you say it, it with still not be true.

Simple question

Do you agree that in our current observable universe there are galaxies that are moving away from each other faster than the speed of light?
Please - yes or no

[Bored chemist]

That's just not true.
And, no matter how many times you say it, it with still not be true.

Simple question

Do you agree that in our current observable universe there are galaxies that are moving away from each other faster than the speed of light?
Please - yes or no

For the sake of discussion we can forego the issue of "from whose point of view".

Yes, I think there are.
And they were got to that speed by an expansion of space time.
https://www.universetoday.com/13808/how-can-galaxies-recede-faster-than-the-speed-of-light/

[Bobolink]

No. It doesn't.
We currently see that activity in our real Universe.
I have already offered an example for that.

OK.  How about this, your hypothesis agrees with the theory of relativity and in addition states that galaxies can move through space a superluminal speeds.  Correct?

[Dave Lev (OP)]

For the sake of discussion we can forego the issue of "from whose point of view".

Yes, I think there are.
And they were got to that speed by an expansion of space time.
https://www.universetoday.com/13808/how-can-galaxies-recede-faster-than-the-speed-of-light/

Wow
Many thanks for this great article
https://www.universetoday.com/13808/how-can-galaxies-recede-faster-than-the-speed-of-light/.
So we have a valid confirmation that far away galaxies are moving away faster than the speed of light.
"As you look at galaxies further and further away, they appear to be moving faster and faster away from us. And it is possible that they could eventually appear to be moving away from us faster than light. At that point, light leaving the distant galaxy would never reach us."
They also claim that this activity doesn't violate the relativity due to the expansion theory:
"This sounds like it breaks Einstein’s theories, but it doesn’t. The galaxies themselves aren’t actually moving very quickly through space, it’s the space itself which is expanding away, and the galaxy is being carried along with it. As long as the galaxy doesn’t try to move quickly through space, no physical laws are broken."

OK.  How about this, your hypothesis agrees with the theory of relativity and in addition states that galaxies can move through space a superluminal speeds.  Correct?

We have got a confirmation for galaxies that are moving faster than the speed of light.
Our scientists claim that this activity doesn't violate relativity due to the expansion.
So do you agree that now we need to discuss why rocket over rocket has the same impact as the expansion?

[Bobolink]

We have got a confirmation for galaxies that are moving faster than the speed of light.

It was never in doubt that the recession velocity of galaxy can exceed c, that has been known for decades.

Our scientists claim that this activity doesn't violate relativity due to the expansion.

Correct, it does not violate relativity, that is taught in the introductory astronomy classes, even 35 years ago when I took one.

So do you agree that now we need to discuss why rocket over rocket has the same impact as the expansion?

I had wanted to discuss your ideas not the BBT, but you really don't seem to.
I fear that this will be a waste of time, because you have not shown a much willingness to change your mind.

OK.

Galaxies move through space, like everything else in space.  For instance the Andromeda galaxy and the Milky Way galaxy are moving through space towards each other at 130 km/sec.  The speed that something can move through space is limited by the speed of light.

The universe is also expanding.  That means that galaxies that are far apart are moving away from each other due the expansion, this is called recession velocity.  Since this movement is not through space it is not limited to the speed of light.

Your idea of rockets shooting rockets means they move through space therefore no matter how many rockets you have you cannot travel at c.

What questions do you have?

[Dave Lev (OP)]

The universe is also expanding.  That means that galaxies that are far apart are moving away from each other due the expansion, this is called recession velocity.  Since this movement is not through space it is not limited to the speed of light.

Well, we don't really know if the Universe is expanding or if the galaxies are expanding
You have already confirmed that our scientists do not measure the space itself.
I hope that you agree that the expansion is measured ONLY by the observable galaxies.
However, our scientists assume that the only explanation for that is space expansion.
I claim that there is no way to set expansion in space as there is no way to set expansion in time. Space is fixed and time is fixed.

Your idea of rockets shooting rockets means they move through space therefore no matter how many rockets you have you cannot travel at c.

The space has no frame.
Therefore, we will never know what is our real velocity with reference to space.
We can just measure our velocity with reference to observable galaxies.
Hence, theoretically, if all the observable galaxies are moving together at one million c in the open space we will not be able to verify it.

I will try to prove that Rocket over rocket works identically as the expansion in place.
Let's look again in the following explanation about the expansion:
https://www.space.com/17884-universe-expansion-speed-hubble-constant.html
"thanks to NASA's Spitzer Space Telescope, and it's a doozy. Space itself is pulling apart at the seams, expanding at a rate of 74.3 plus or minus 2.1 kilometers (46.2 plus or minus 1.3 miles) per second per megaparsec (a megaparsec is roughly 3 million light-years)."

Therefore, the expanding rate is about 75 kilometers per second per 3 million light years.
1 Day = 86400 Seconds
In one day the expansion rate is 75 x 86,400 = 6,480,000 km
1 Year = 365 days
In 1,000 years = 365 10^3 days. So, in one 1,000 years the expansion is: 6,480,000 * 365 *10^3 = 2.3652 * 10 ^12 km
We know that 1 Light Year = 9.4605E+12 Kilometers
We also know that the expanding rate is about 75 kilometers per second per 3 million light year.
Therefore, 3 Million LY means
9.4605 10^12 * 3 = 28.3815 10^12 km
So, in order for the expansion to multiply the size 3LY, we need:
1,000 year * 28.3815 10^12 km / 2.3652 * 10 ^12 km= 12,000 Years
Hence, 12,000 years are needed for the expansion to multiply the distance of two nearby galaxies from 3Light years to 6 Light years.
So, in 12,000 years a Volume of the 3x3x3 = 27 Ly cube had been increased to 6x6x6 = 216 ly
Therefore, in every 12,000 years the volume of our space is increasing by 6^3/ 3^3 = 3^2 = 8
So, let's see the meaning of this expansion:

Based on this key information about the expansion in space, let's compare this theory to Rocket over rocket

Let's assume that we have only 6 galaxies in the Universe that are located exactly at the edges of a 3x3x3 LY cube
Those galaxies aren't moving in space and there are no other galaxies in all the infinite space
Each galaxy is just located at other side of the 3x3x3 ly Cube
One up, one down, one left, one right one inside one outside.
They stay there without any movement.
Now we will try to verify the impact of space expansion Vs rocket over rocket.
Action 1
Space expansion:
Let's start the timer of the expansion is space of 75 kilometers/ sec while the whole universe size is 3x3x3 Ly:
Due to this expansion in space, each galaxy is moving now at those 75 kilometers/sec in its direction.
After 12,000 years the space cube of 3x3x3 will be increased to 6x6x6.
Therefore we will get the galaxies at the edge of that cube.
One up, one down, one left, one right one inside one outside while each one of them is moving at 75 kilometers/sec in its direction.

Rocket over rocket or galaxy over galaxy:
In this case, let's assume that we only fire just one rocket/galaxy at a time from each galaxy and in the direction of the expansion.
Let's start the timer of the rocket over rocket:
The galaxy that is located upwards, should fire a new rocket/galaxy upwards at 75 kilometers/sec.
The galaxy that is located downwards, should fire a new rocket/galaxy downwards at 75 kilometers/sec.

The galaxy that is located at the lefts, should fire a new rocket/galaxy to the left at 75 kilometers/sec.

The galaxy that is located at the right, should fire a new rocket/galaxy to the right at 75 kilometers/sec.
And so on
Therefore, after 12,000 years we should get the new rockets/ galaxies exactly at the edge of the 6x6x6 cube while each one of them is moving at a velocity of 75Km/sec
One up, one down, one left, one right one inside one outside - each one of them is moving at 75 kilometers in its direction.
So far Rocket over rocket is identical to space expansion.

Action 2
Space expansion:
After the next 12,000 years  the space cube of 6x6x6 will be increased to 12x12x12 while the recession velocity of galaxy at each edge of the cube should be 75x2 = 150 Km/sec.
Therefore we will get the galaxies at the edge of that 12x12x12 cube.
One up, one down, one left, one right one inside one outside while each one of them is moving at 150 kilometers/sec in its direction.

Rocket over rocket or galaxy over galaxy:
Let's fire the next cycle of rocket over rocket or galaxy over galaxy:

We already know that the galaxy that is located upwards is moving upwards at 75 Km/s. As it fires its new rocket/galaxy in the same direction of its movement - (upwards) , than this new rocket/galaxy should move now at 150 km/sec. (75+75 = 150)
Same issue with any galaxy at any side.
So, as the velocity of each new rocket/galaxy is twice the speed of 75 Km/sec, than after 12,000 years each one of them should cross exactly 6 LY
Therefore, after the next 12,000 years the new fired rockets will set a perfect cube of 12x12x12 LY  (6+6 x 6+6 x 6+6) while their velocity is 150 Km/s (each one - in each direction)
This is also identical to space expansion.
I could go on and on and you will find that after any time frame of 12,000 years we get exactly the same impact as the space expansion.
Therefore, if space expansion is identical to rocket over rocket system, than their outcome should be identical.
As the expansion in space can set a recession velocity of galaxy that exceeds c, than the rocket over rocket can do it without any difficulties.