Conceptual problems

Speed is meters/second.

Constant speed means a body is moving say 10 meters in a second.

If the "meters" however are "expanding" what does speed mean?

If in a second 10 meters become 10.00000x meters, the speed
of a body with constant velocity is slowing down.

The body puts 10 meters in each second but since each of
those meters has grown bigger, its effective velocity is
9.999999999x meters?

In an expanding universe everything is slowing down then ?

But then, how can we measure the expanding meters?
If we say 1 meter expanded to 1.00000x meter, what
does THAT mean?

Does it mean that in TRUE, non expanding meters, the distance
between point A and B that was BEFORE 10 meters has grown
to 10.000000x "standard" non expanding meters?

Space expansion does not happen within our measurement
meters I suppose. The meter in Paris has the same size
as it had when it was created.

But does it?

Space has expanded in those centuries since that thing was
cast. Has our meter shrunk then?

Note that this are conceptual problems. It doesn't matter
if somebody says that the expansion is so small that
we can't measure it...

The choice of a unit of measure is arbitrary. I could say that
my choice of unit, instead of the old fashioned meters,
is the distance between my keyboard here and the center
of the Virgo cluster. I would use the unit
1 V for Virgo. Yes, it would be impractical in everyday life
but nice for cosmological problems :-)

And nothing prevents me from choosing such a unit.

Then, due to space expansion, 1V grows by some centimeters
each second.

How much is the speed of an object expressed in Vs?

If I move with 1e-1500000000000000000000000 V /second
to bring my daughter from school in my motorcycle, each
second my speed is changing, my motorcycle slowing down
a bit since my unit of measure is expanding!

Up to now all the answers I got was that space expansion
happens far away, where we can't see it, in the immense voids
between galaxies.

In another words:

"do not worry jacob. Space is expanding but physics goes on
as usual"

They propose two kinds of space units:

a) Small ones like the one in Paris, that do not expand at all.

b) Big units like the "V" unit above, that shouldn't be used.
They are unreliable because they expand...

How can we know for sure when a unit starts to expand and
when it stays the same?

i.e. at WHICH SIZE in non expanding meters does a unit begin
to "feel" space expansion???

That is kind of difficult question. Most BB people get
angry at this point and cut the conversation.

When I speak about common sense I mean logic, not prejudice.

I am ready to accept far fetched conclusions, even that space
is expanding when logic would be preserved.

jacob