Hypothetical astrophysics question

John Griffin wrote:

Two tiny, fuzzy points of light are observed. Observations of
each object indicate that it's a globular galaxy ten billion light
years distant. The first one is exactly that, but the second one
happens to be another entire universe. It's 100,000 times as
far away as the galaxy, and it's emiting ten billion times as
much light. Is there anything that would distinguish these
objects from one another?

Redshift. The universe is expanding, and there is more space in
between us and the object 100,000 times as far away; it would appear to be
more redshifted.
--
-- With Best Regards,
Matthew Funke )

"John Griffin" wrote in message
...

Two tiny, fuzzy points of light are observed. Observations of
each object indicate that it's a globular galaxy ten billion light
years distant. The first one is exactly that, but the second one
happens to be another entire universe. It's 100,000 times as
far away as the galaxy, and it's emitting ten billion times as
much light. Is there anything that would distinguish these
objects from one another?

I'm just curious. I haven't seen anything like that, as
far as I know.

Well, by current theory it would be an impossible observation
for several reasons. For instance, our cosmic viewing horizon
is at just about 13.7BLY, so nothing can be seen that's
further. Also, to judge its distance, presumably you would
rely on the hubble red-shift. At the stated distance, if the
cosmic horizon wasn't a factor, the red-shift would be extreme --
there'd be almost nothing left of the light energy to detect. Not
to mention the fact that if you're seeing it, it's *in* our
universe and not a separate universe.

"John Griffin" wrote in sci.astro:


Two tiny, fuzzy points of light are observed. Observations of
each object indicate that it's a globular galaxy ten billion light
years distant. The first one is exactly that, but the second one
happens to be another entire universe. It's 100,000 times as
far away as the galaxy, and it's emiting ten billion times as
much light. Is there anything that would distinguish these
objects from one another?


Our current understanding tells us that it's impossible to look outside our
own universe. It also tells us that there's at least a horizon to our view
due to the age and expansion rate of our universe that is around 13 billion
lightyears.

--
CeeBee


Uxbridge: "By God, sir, I've lost my leg!"
Wellington: "By God, sir, so you have!"


Google CeeBee @ www.geocities.com/ceebee_2

Matthew F Funke replied to John Griffin:

Two tiny, fuzzy points of light are observed. Observations of
each object indicate that it's a globular galaxy ten billion light
years distant. The first one is exactly that, but the second one
happens to be another entire universe. It's 100,000 times as
far away as the galaxy, and it's emiting ten billion times as
much light. Is there anything that would distinguish these
objects from one another?

Redshift. The universe is expanding, and there is more space
in between us and the object 100,000 times as far away; it would
appear to be more redshifted.

Why would it necessarily be redshifted at all? Since it's a
different universe, it didn't take part in the Big Bang. It
may have had its own Big Bang a quadrillion years or so ago,
in which case its near side could be moving toward us at high
speed. The two universes could even be moving toward or away
from each other overall.

-- Jeff, in Minneapolis

..

Greg Neill replied to John Griffin:

Two tiny, fuzzy points of light are observed. Observations of
each object indicate that it's a globular galaxy ten billion light
years distant. The first one is exactly that, but the second one
happens to be another entire universe. It's 100,000 times as
far away as the galaxy, and it's emitting ten billion times as
much light. Is there anything that would distinguish these
objects from one another?

I'm just curious. I haven't seen anything like that, as
far as I know.

Well, by current theory it would be an impossible observation
for several reasons. For instance, our cosmic viewing horizon
is at just about 13.7BLY, so nothing can be seen that's
further.

That "horizon" is imposed by the light travel time since the
plasma cleared up after the Big Bang. Light from a separate
universe, not involved in our Big Bang, would be temporarily
blocked by the plasma, but once the plasma cleared, the light
would get through. I don't know whether the geometry of the
situation would allow the light to reach us in a finite time.
It may depend on the size and history of our Universe.

Also, to judge its distance, presumably you would rely on the
hubble red-shift.

Which would be completely usesless, since a separate universe
would have no connection to the Big Bang which got our Universe
started. No way to correlate redshift with distance.

At the stated distance, if the cosmic horizon wasn't a factor,
the red-shift would be extreme -- there'd be almost nothing
left of the light energy to detect.

Or it might be extremely blue-shifted. Or anything in between.

Not to mention the fact that if you're seeing it, it's *in* our
universe and not a separate universe.

Under *some* definitions of "universe". Not all.

Clearly, this imaginary thing had no part in our Big Bang, and
existed some time before our Big Bang occurred. I think that
calling it a "universe" is entirely reasonable, and I think
that such other universes could very well exist-- perhaps
infinitely many of them, if space is infinite. Whether we
would be able to see such a distant universe is a question
I'm not sure anyone can answer until we understand the nature
of our own Universe a bit better.

-- Jeff, in Minneapolis

..

CeeBee replied to John Griffin:

Two tiny, fuzzy points of light are observed. Observations of
each object indicate that it's a globular galaxy ten billion light
years distant. The first one is exactly that, but the second one
happens to be another entire universe. It's 100,000 times as
far away as the galaxy, and it's emiting ten billion times as
much light. Is there anything that would distinguish these
objects from one another?

Our current understanding tells us that it's impossible to look
outside our own universe.

Maybe. The plasma of our Universe early in its history may
have blocked the light from anything outside it. Maybe.

It also tells us that there's at least a horizon to our view
due to the age and expansion rate of our universe that is around
13 billion lightyears.

But that only applies to light originating from some object
which took part in OUR Big Bang. It doesn't apply to any
other universe.

-- Jeff, in Minneapolis

..

"Jeff Root" wrote in message
om...
Greg Neill replied to John Griffin:

Two tiny, fuzzy points of light are observed. Observations of
each object indicate that it's a globular galaxy ten billion light
years distant. The first one is exactly that, but the second one
happens to be another entire universe. It's 100,000 times as
far away as the galaxy, and it's emitting ten billion times as
much light. Is there anything that would distinguish these
objects from one another?

I'm just curious. I haven't seen anything like that, as
far as I know.

Well, by current theory it would be an impossible observation
for several reasons. For instance, our cosmic viewing horizon
is at just about 13.7BLY, so nothing can be seen that's
further.

That "horizon" is imposed by the light travel time since the
plasma cleared up after the Big Bang. Light from a separate
universe, not involved in our Big Bang, would be temporarily
blocked by the plasma, but once the plasma cleared, the light
would get through. I don't know whether the geometry of the
situation would allow the light to reach us in a finite time.
It may depend on the size and history of our Universe.

Also, to judge its distance, presumably you would rely on the
hubble red-shift.

Which would be completely usesless, since a separate universe
would have no connection to the Big Bang which got our Universe
started. No way to correlate redshift with distance.

At the stated distance, if the cosmic horizon wasn't a factor,
the red-shift would be extreme -- there'd be almost nothing
left of the light energy to detect.

Or it might be extremely blue-shifted. Or anything in between.

Not to mention the fact that if you're seeing it, it's *in* our
universe and not a separate universe.

Under *some* definitions of "universe". Not all.

Clearly, this imaginary thing had no part in our Big Bang, and
existed some time before our Big Bang occurred. I think that
calling it a "universe" is entirely reasonable, and I think
that such other universes could very well exist-- perhaps
infinitely many of them, if space is infinite. Whether we
would be able to see such a distant universe is a question
I'm not sure anyone can answer until we understand the nature
of our own Universe a bit better.

The usual definition applied to our universe is that it
contains everything. If the BB scenario is taken to
describe it, space itself was created and began evolving
at the moment of the BB. If so, there is no space for
this other universe to pre-exist in, in our frame of
reference. Certainly it could not exist in our universe
and be a universe itself. There can be no connection betwixt
or between, so no path for light to follow.

The plasma haze you refer to encompassed all of space
existing at the time, and before it things just get worse.
Even if anything were "outside" and shining in, our
universe is likely immensely larger than our teensy
drop-in-the-ocean cosmic horizon. Light entering our
universe after the decoupling of matter and light would
have unimaginable numbers of light years to travel to
get to us, all of it in space that is moving away from
us at more that the speed of light outside the horizon;
it simply could not get here.

Jeff Root wrote:
Matthew F Funke replied to John Griffin:

Two tiny, fuzzy points of light are observed. Observations of
each object indicate that it's a globular galaxy ten billion light
years distant. The first one is exactly that, but the second one
happens to be another entire universe. It's 100,000 times as
far away as the galaxy, and it's emiting ten billion times as
much light. Is there anything that would distinguish these
objects from one another?

Redshift. The universe is expanding, and there is more space
in between us and the object 100,000 times as far away; it would
appear to be more redshifted.

Why would it necessarily be redshifted at all? Since it's a
different universe, it didn't take part in the Big Bang. It
may have had its own Big Bang a quadrillion years or so ago,
in which case its near side could be moving toward us at high
speed. The two universes could even be moving toward or away
from each other overall.

To be honest, I took the OP's "another entire universe" to be a
poetic description of its scale. If it were, in fact, another universe,
we wouldn't be able to see it as a fuzzy point of light -- or anything
else, for that matter. The entire question would be irrelevant;
information (including light information) doesn't go between universes.

Not to mention that spacetime is a function of being within a
universe (assuming it's one like ours); speaking of universes moving
"toward or away from each other" would be nonsensical.
--
-- With Best Regards,
Matthew Funke )

"Matthew F Funke" wrote in message
...
Jeff Root wrote:
Matthew F Funke replied to John Griffin:

Two tiny, fuzzy points of light are observed. Observations of
each object indicate that it's a globular galaxy ten billion light
years distant. The first one is exactly that, but the second one
happens to be another entire universe. It's 100,000 times as
far away as the galaxy, and it's emiting ten billion times as
much light. Is there anything that would distinguish these
objects from one another?

Redshift. The universe is expanding, and there is more space
in between us and the object 100,000 times as far away; it would
appear to be more redshifted.

Why would it necessarily be redshifted at all? Since it's a
different universe, it didn't take part in the Big Bang. It
may have had its own Big Bang a quadrillion years or so ago,
in which case its near side could be moving toward us at high
speed. The two universes could even be moving toward or away
from each other overall.

To be honest, I took the OP's "another entire universe" to be a
poetic description of its scale. If it were, in fact, another universe,
we wouldn't be able to see it as a fuzzy point of light -- or anything
else, for that matter. The entire question would be irrelevant;
information (including light information) doesn't go between universes.

I was thinking of a universe as another collection of galaxies
and stuff, with its own origin (big bang or whatever) occupying
another part of the infinite space this one is in.

It seems to me that you're saying light emitted by a universe
stops or vanishes at some kind of boundary. (A universal
event horizon?) I don't know if that's a consequence of the
big bang theory, common sense, or just a conjecture. If
it has to do with the curvature of space, can the path of a
photon that doesn't collide with another object in the galaxy
be described?

I don't understand why this universe wouldn't be visible from
"outside."

Not to mention that spacetime is a function of being within a
universe (assuming it's one like ours); speaking of universes moving
"toward or away from each other" would be nonsensical.

If photons don't stop at "the edge of the universe," what would
prevent them from entering another one when they encountered
it?

Can you refer me to a website or some literature that addresses
those questions?

John Griffin wrote:

I was thinking of a universe as another collection of galaxies
and stuff, with its own origin (big bang or whatever) occupying
another part of the infinite space this one is in.

This universe isn't just "in" space. Space was created during the
Big Bang. Space doesn't "surround" the universe; space is *part of* the
universe.

It seems to me that you're saying light emitted by a universe
stops or vanishes at some kind of boundary. (A universal
event horizon?) I don't know if that's a consequence of the
big bang theory, common sense, or just a conjecture.

AIUI, it's common sense. If the Big Bang created space, then outside
the universe, there's no space for light to travel in.

I don't understand why this universe wouldn't be visible from
"outside."

What would the light travel through? What allows the light to
perpetuate outside the universe?

There's also the problem that universes can have radically different
natural laws, so we have no idea how EM waves would behave in that "other
universe", even if one ignores what happens to it when it tries to get
from one universe to another.

Can you refer me to a website or some literature that addresses
those questions?

Try the Cosmology FAQ as a starting point:
http://www.astro.ucla.edu/~wright/cosmology_faq.html

It even has a good bibliography. And it's written by people you
can take much, much more seriously than me.
--
-- With Best Regards,
Matthew Funke )