But... how can we KNOW what is out there NOW?

I don't think M-31 ripping apart X-1 years ago would do anything
except provide a beautiful display for us in the night sky...after all,
its still X light-years distant from us. Where X = about 3 million ly.
(So wouldn't it be a 'pleasant' surprise? ) Probably not a good idea to
any inhabitants of M-31 though! Although there demise would have been
about 3 million years ago.

No, according to confirmed, and re-confirmed, laws of physics,
nothing can travel faster than light, no matter how slow it seems to
you. (However, what's your hurry? Time slows to zero the closer you
get to light speed, so......).

"The speed of Light"...not just a good idea, ITS THE LAW!"
Clear skies,
Tom W.




Scribe2b wrote:

Similarly, time is also relative. We think of "now" having meaning, but

it's really just an illusion. All human beings are relatively close to
one another and moving at about the same speed. So we can cheat and
define a common "now."


still, i ask, if light travels X number of years from Andromeda to reach us,
and if Andromeda ripped itself apart X-1 years ago in our time, then next year
we would be in for a very unplesant surtprise.

is there no way to detect such events other than waiting upon the speed of
light?

jc

Shankar Bhattacharyya wrote:
Absolute proofs exist only in mathematics and in formal logic, but
not in the natural sciences.

Would you actually claim that that is really true of mathematics and
formal logic?

Mathematics depends on a set of axioms. Axioms are "obvious
assumptions". Formal logic provides the tools of inference by which we
extend axioms into theorems and evaluate information for consistency,
implication, so on so forth.

The absolute proofs of mathematics depend on the assumptions.

In some sense, in possibly some situations, maybe in many, the proofs
may not depend on the assumptions, in a mechanistic sense. However, what
the proofs prove presumably does depend on the assumptions. Otherwise we
would not need axioms.

I think the crux of the matter is not whether assumptions are made.
Rather, I see the difference as follows. In the natural sciences, there
is in some sense a set of factual truths, which we seek to discover.
Because nature is under no constraint to make these truths follow any
specific pattern, we can never "prove" any such pattern. We can only
assume those patterns hold until countervailing evidence appears.

In mathematics, on the other hand, we humans are in a more creative
position. We define the axioms. They are not "out there" for us to
find, although we may attempt to define them in such a way that they
model some facet of reality. For example, we can either assume the
Axiom of Choice, or not. Either way is valid, but our decision has a
definite and tangible impact on which things we can represent in our
theory, and which things we cannot.

Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

In article ,
Shankar Bhattacharyya wrote:
(Paul Schlyter) wrote in
:


And that's the case with all our knowledge: it's based on at least
_some_ assumptions, assumptions which appears to remain valid
through an extremely large number of observations and therefore we
trust them. But we're still dependent on these assumptions.

Absolute proofs exist only in mathematics and in formal logic, but
not in the natural sciences.

Would you actually claim that that is really true of mathematics and
formal logic?

Mathematics depends on a set of axioms. Axioms are "obvious
assumptions". Formal logic provides the tools of inference by which we
extend axioms into theorems and evaluate information for consistency,
implication, so on so forth.

The absolute proofs of mathematics depend on the assumptions.

In some sense, in possibly some situations, maybe in many, the proofs
may not depend on the assumptions, in a mechanistic sense. However, what
the proofs prove presumably does depend on the assumptions. Otherwise we
would not need axioms.

You're right here, of course: the axioms of mathematics defines the
"universe" which mathematics "lives" in. You can change the axioms
and get another "math universe" which is equally valid and sometimes
even can be useful. One good example is Euclids parallell axiom:
"Through a point beside a line, one can draw exactly N lines parallell
to the first line" where N=1 for classical plane geometry. By
changing N to 0 you instead get e.g. spherical geometry, and by
setting N to "larger than 1" you get the open, "saddle-shaped" geometry.
These alternate geometries were mathematical curiosities when first
invented, but later turned out to be useful for e.g. cosmology.

Anyway, my real point wasn't about the existence or non-existence of
axioms, but about the existence or non-existence of absolute proofs:
such proofs exist only in math and formal logic (with suitable axioms
of course). They don't exist in sciences attempting to deal with the
real world, such as physics, chemistry, biology, psychology, sociology
which attempt to deal with, in turn, more and more complex systems.

--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://www.stjarnhimlen.se/
http://home.tiscali.se/pausch/

"Greg Crinklaw" wrote in message
...
If you are truly interested in the answer to this and other questions I
suggest you visit your nearest college bookstore and purchase a basic
101 astronomy text. They are all written at level most people can
readily understand and there is little/no math.

Is having "little or no math" really a benefit, Greg?

Personally I often find a mathematical description of something to be a far
clearer and unambiguous explanation of it than a page of words whose meaning
is far less precise, and which is open to misinterpretation.

Maths is a powerful tool, and it's really nothing to be scared of, is it?

If we didn't have a mathematical description of the motion of the sky, you
and I certainly wouldn't be writing the software that we are today :-).

Regards,

Chris

"Scribe2b" wrote in message
...

is there no way to detect such events other than waiting upon the speed
of
light?

The General Theory of Relativity tells us that information cannot be
transmitted faster than the speed of light. GR has stood up flawlessly to a
century of experimental verification so far.

Regards,

Chris

Not at all. "Now" is non trivial. It's relative just like "where".
You ask, where is Omega Cen? It is appropriate to ask in return,
relative to what? The center of the galaxy? The sun? The earth?

All such comparisons must be relative to the location of the observer. This
does not require a center, nor an edge, nor a time.

Clear, Dark, Steady Skies!
(And considerate neighbors!!!)

Sure, it makes sense to me. Another way of looking at it is that a
fundamental property of the Universe is that every observer believes
he/she is at it's center. That thought always brings a chuckle...
explains a lot doesn't it? ;-)

If you are observing from the center of your universe, then whare ARE you
observing from??

Clear, Dark, Steady Skies!
(And considerate neighbors!!!)

Scribe2b wrote::

so... we see fossil light.
a vast array of billions of galaxies and all the rest.
ancient light reveals millions or billions of images of what was.

but what about NOW?

how do we know that, for instance, andromeda is still there?
how do we know that it hasnt exploded and the first tremors of a tidal wave of
energy arent headed this way?

rather than the most brilliant informed assumptions, i am asking how do we know
about NOW?
are there concrete means of calculation?
means of sensing reality beyond waiting for the lightspeed messabes to arrive?

most people seem to rationalize--- best-guessing gropes for generalizations
based upon solar system objects or localized phenomena--- a visibility within
nanoseconds, or hopeful intrapolations to support probability, etc.

but...
can we prove--- without assumptions or the most imformed guessing--- that
remote objects whose ancient ghost images we observe--- exist NOW???


It would be nice to have instantaneous knowledge of what's out there
NOW, but the limited speed of light, though it bars us from knowing
NOW, does give us a wider window on the universe. Without it we would
not be able to see events that happened billions of years ago. Our
view of the universe, limited to NOW, might be much less rich than it
is, er... now.

Of course, maybe things going on out there NOW have suddenly started
to pick up and the NOW Universe is much richer in events than it has
been in the past. Only, we are prevented from knowing this because we
haven't gotten the news yet. This doesn't seem likely.

It would be nice to have instantaneous information from the far flung
universe as well as being able to retain our stretched-out window on
the past. But one of the ruling principles of the universe seems to be
that you can't have it all. So, putting it to a vote, which would you
rather have: instantaneous news from the edge of a possibly much
bigger universe or stale news from a possibly much more varied past?

Of course, these considerations are apart from the grosser effects of
an infinite light speed. What would be the effects of instantaneous
light transmission on the normal mechanical and chemical processes of
our world?

If all the gamma rays, x-rays, etc. of the NOW universe were delivered
to us instantly would we be getting a larger (or smaller) dose than we
do now, having them arrive from many events spread out in the past?
Would the skies be brighter in an instantaneous lightspeed universe or
dimmer? More variable? Guess it depends on the "true" size of the
universe. (Anyone have an idea on what size an instantaneous
lightspeed universe would need to be in order to deliver to us the
amount of photons we are currently receiving from our time-delayed
universe? Guess it depends on the rate of stellar processes now vs.
the past.)

Not to mention the effects of instantaneous light speed on sub-atomic
processes (because I don't have a clue). That might be a whole nuther
can of worms.

--
kandr

So, putting it to a vote, which would you
rather have: instantaneous news from the edge of a possibly much
bigger universe or stale news from a possibly much more varied past?

i would rather have both.
1--- the ancient fossil light for astro-archaeology.
2--- an immediate relevant source of imaging for NOW.
then we would know a great deal more
jc

Well, it seems that your doomed to see what you call "ancient fossil light " as
even Light itself has a limit of the speed it can go. Heck, while short, look at
the time it takes light to reach Earth from our own sun.



--
"In this universe the night was falling,the shadows were lengthening
towards an east that would not know another dawn.
But elsewhere the stars were still young and the light of morning
lingered: and along the path he once had followed, man would one day go
again."

Arthur C. Clarke, The City & The Stars

SIAR
www.starlords.org
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http://www.freelancewrittersshop.netfirms.com
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"Scribe2b" wrote in message
...
So, putting it to a vote, which would you
rather have: instantaneous news from the edge of a possibly much
bigger universe or stale news from a possibly much more varied past?

i would rather have both.
1--- the ancient fossil light for astro-archaeology.
2--- an immediate relevant source of imaging for NOW.
then we would know a great deal more
jc



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