Are there any points in the universe that can't be reached...

By light?

Like is there a "delta" zone nearby black holes where light can't get
through?

On 20 Sep 2006 04:05:20 -0700, in uk.sci.astronomy ,
wrote:

By light?

please put the question into the message body, not all newsreaders
display the subject conveniently when you're reading /replying to
messages.

Like is there a "delta" zone nearby black holes where light can't get
through?

Light is just a form of energy. So it would have to be a place where
there was no energy. So no.
--
Mark McIntyre

Depends on what you mean.

If the question is "...ANY light...?", that's one thing.

If the question is "...any light from any PARTICULAR source...?" then
light cones come into it, and the answer is that it is possible
for THAT light never to reach some places, IIRC. BIMNHRC!

In message , Mark McIntyre
writes
On 20 Sep 2006 04:05:20 -0700, in uk.sci.astronomy ,
wrote:

By light?

please put the question into the message body, not all newsreaders
display the subject conveniently when you're reading /replying to
messages.

Like is there a "delta" zone nearby black holes where light can't get
through?

Light is just a form of energy. So it would have to be a place where
there was no energy. So no.

It sounds as if the OP has found some kook site, but I'll just note that
visible light can't reach us from the galactic centre (or other areas
behind lots of cosmic dust). Other types of radiation reach us, of
course, such as infrared http://www.mpe.mpg.de/ir/GC/index.php
Nothing can reach us from inside a black hole event horizon, either.
A quick web search for "delta zone" didn't find anything useful -
perhaps you could enlighten us (sorry !) about your source.

"Jonathan Silverlight" wrote
in message ...
| In message , Mark McIntyre
| writes
| On 20 Sep 2006 04:05:20 -0700, in uk.sci.astronomy ,
| wrote:
|
| By light?
|
| please put the question into the message body, not all newsreaders
| display the subject conveniently when you're reading /replying to
| messages.
|
| Like is there a "delta" zone nearby black holes where light can't get
| through?
|
| Light is just a form of energy. So it would have to be a place where
| there was no energy. So no.
|
| It sounds as if the OP has found some kook site, but I'll just note that
| visible light can't reach us from the galactic centre (or other areas
| behind lots of cosmic dust). Other types of radiation reach us, of
| course, such as infrared http://www.mpe.mpg.de/ir/GC/index.php
| Nothing can reach us from inside a black hole event horizon, either.
| A quick web search for "delta zone" didn't find anything useful -
| perhaps you could enlighten us (sorry !) about your source.

Trawling by good old-fashioned memory (not Google) through cosmology
articles I have read.

It can be shown that there are parts of the universe which you cannot reach.
Perhaps you could have done in the past, but the opportunity to do so (from
here) is now lost forever.

I think most of us know that the universe is expanding, making distant
galaxies appear to recede from us, and that the rate of this expansion
appears to increase with distance. Doing the maths brings us to an "event
horizon" at which any parts of the universe further away appear to recede
faster than the speed of light. As we can't go that fast, we can never reach
those parts, starting now and from here.

The apparent position of this "event horizon" changes with time, according
to the total mass of the universe and doubtless other factors too. But those
parts of the universe near that horizon will be carried past it by their
continued recession from us. So there are some parts of the universe we
might once have been able to travel to, but cannot now (barring "wormholes"
or other freaks of cosmic geography).

Some have used this reasoning to argue that the whole universe is a "black
hole". So where are the tidal forces? The larger the black hole, the less
noticeable these forces are unless you are close to the "singularity" at its
centre. The universe we can observe is very large indeed, so the tidal
forces would be vanishingly small away from the "singularity". As there is
nothing we can see that suggests such a "singularity" is anywhere near us,
there would be nothing obvious to our senses to tell us whether this is, or
is not, the case.

An extension of this is the "black death" of the Universe when its expansion
carries just about everything else beyond this horizon, separating us
forever from all other matter and sources of energy. This is unlikely to
happen any time soon - long beforehand all the sources of energy such as
nuclear fusion in stars are likely to have been exhausted.
--
- Yokel -
oo oo
OOO OOO
OO 0 OO
) ( I ) (
) ( /\ ) (

"Yokel" now posts via a spam-trap account.
Replace my alias with stevejudd to reply.

In message , Yokel
writes

"Jonathan Silverlight" wrote
in message ...
| In message , Mark McIntyre
| writes
| On 20 Sep 2006 04:05:20 -0700, in uk.sci.astronomy ,
| wrote:
|
| By light?
|
| please put the question into the message body, not all newsreaders
| display the subject conveniently when you're reading /replying to
| messages.
|
| Like is there a "delta" zone nearby black holes where light can't get
| through?
|
| Light is just a form of energy. So it would have to be a place where
| there was no energy. So no.
|
| It sounds as if the OP has found some kook site, but I'll just note that
| visible light can't reach us from the galactic centre (or other areas
| behind lots of cosmic dust). Other types of radiation reach us, of
| course, such as infrared http://www.mpe.mpg.de/ir/GC/index.php
| Nothing can reach us from inside a black hole event horizon, either.
| A quick web search for "delta zone" didn't find anything useful -
| perhaps you could enlighten us (sorry !) about your source.

I think most of us know that the universe is expanding, making distant
galaxies appear to recede from us, and that the rate of this expansion
appears to increase with distance.

I can't resist noting that expansion is only the simplest explanation
for the cosmological red shift, but that's getting off topic for the
question! Even if something else is causing the red shift, the result is
the same, AIUI. "You can't get there from here".