One thing that has always eluded my understanding is that isn't the universe an ever expanding sphere with us constantly moving within it. So wouldn't we see different lines of sight from our relative position each time we make an observation or take a distance measurement. What formulas have been constructed for this?

The universe is not a sphere - it just is an expanding existence. If it were a sphere, that would imply an edge, or boundary, and that doesn't exist, even though it has a size! It also has no center. We are on a planet that rotates, and revolves around the sun in a solar system that revolves around the center of our galaxy, etc., so we really can never quite look at the things quite the same way. The line of sight is never the same. Astronomycast.com has had a number of episodes dealing with how distance is measured, the shape of universe, and so forth.

Hi Clegrand

Google 'Hubbles Law' and 'redshift'. There is a ton of good stuff about this. It was just the kind of observation you're talking about that led to the discovery of the expanding universe. Hubble observed in 1929 that distant galaxies in all directions were accelerating away from the Milky Way, showing that contrary to what scientists believed, the universe was expanding. Einstein's own calculations had shown him the universe must expand or contract, but he didn't trust them - until Hubble's observations. So your intuition is bang on!

Our 'observable' universe is spherical, but this is simply a function of time and the finite speed of light - we can only see as far as light has been able to travel in all directions over the age of the universe. The actual 'shape' of space is not thought to be spherical, but rather is flat with a margin of error of about 2% I think, over the entire universe that we can see. Space can take the shape of a cube or donut or soccer ball for example, while remaining 'flat' (or Euclidean), finite, and unbounded.

It still could be a sphere as I understand it - just a bloody big one, so big it appears flat on the scale of the observable universe!

Weird huh?

Pamela and Fraser, in the latest podcast talk about how the shape of space exists in multiple dimensions that are impossible for our three dimensional brains to visualise - other than to compare them to familiar three dimensional shapes like spheres and donuts and soccer balls. You have to consider just the 'surface' of the shape, which is two dimensional in our three dimensional space, then extrapolate it to higher dimensions. Then your brain melts.

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If something is in me which can be called religious then it is the unbounded admiration for the structure of the world so far as our science can reveal it... of the manifestations of the profoundest reason and the most radiant beauty, which are only accessible to our reason in their most elementary forms...
Albert Einstein

How about this -

We observe distant galaxies to recede at greater than c.

Photons from distant galaxies are stretched (red-shift).

However, we observe photons always move at c relative to Earth. Therefore relativity is not violated on Earth.

We accept the cosmological principle that Earth does not occupy a special place in the universe, which we observe to be homogenous and isotropic.

Therefore we conclude that photons must also move at c relative to distant galaxies, where relativity is also unviolated.

Hence, the space between distant galaxies has stretched.

General relativity supports that spacetime is elastic, and predicts that the universe must expand or contract except in the special case where the density and distribution of matter in the entire universe is perfect, virtually to the atom (which in any case would be violated the instant a heavenly body moved, thereby triggering a gravitational collapse of the entire universe).

Why?

Because.



...don't mention dark energy...



...and I'm not sure we don't have a global reference frame - what about the CMBR? Don't we share co-moving co-ordinates or something?

__________________
If something is in me which can be called religious then it is the unbounded admiration for the structure of the world so far as our science can reveal it... of the manifestations of the profoundest reason and the most radiant beauty, which are only accessible to our reason in their most elementary forms...
Albert Einstein

who said cricket?

Exactly! - where supposedly 3-percent of the universe we can see due to the galaxies traveling less than speed of light.

where does the 3-percent come from????????????? - hw de we know (or thing) that the rest of the 97-percent of the universe is beyond that "C" event horizon? - since we cannot observe galaxies that are receeding at rates greater than light speed.

I assume there could be an empirical "proof" of the assirtion that there is a universe beyond what we can observe (not that 3-percent - which I would welcome an answer to how you get that "assumption" - vs 30 percent or 0.00000003 percent of whatwe see is what is there) would be validated if one of there galaxies we now see decides to "dissapear" (due to the increasing expansion of the universe where the distant galaxy exceeds the speed of light (note the most distant galaxies now are in the ifrared.......................I assume we will find one in a lower radio spectrum - maybe radio.....on the "edge" (not of the universe but of our observable universe))..................and in a few million or billion years that radio source will eventually "end" WRT to us.

I assume one who lives on that galaxy WAY over at that edge of that 97-percent we cannot see.........would see a sky filled with only stars and galaxies over one half of the sky (and the flipped version of one at the other edge of the universe).

...............where we sit in the universe is not difinable from oversation.

in the center? - near one edge or near the other??????????????

....................


my question is WHERE DOES THE ASSUMED "WHAT WE SEE IS 3-PERCENT OF THE UNIVERSE".......................................ho w do make such a claim when the other 97-percent is theortically unobservable???????????

In the immortal words of Garfield, "I'm not overweight, I'm undertall"!

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The Brain Science Podcast

Hey FriedPhoton,

It wasn't always this way. I'm working on an ATM that gravity is increasing.

__________________
If something is in me which can be called religious then it is the unbounded admiration for the structure of the world so far as our science can reveal it... of the manifestations of the profoundest reason and the most radiant beauty, which are only accessible to our reason in their most elementary forms...
Albert Einstein

Yea, yea... that's the ticket, gravity's increasing.

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The only way of finding the limits of the possible is by going beyond them into the impossible.

Arthur C. Clarke

The Brain Science Podcast

Mmm, okay, so for example...

Say, 10 billion years ago, a supergiant star went supernova in the halo of a young galaxy and sends photons that the Hubble Space Telescope focuses and images today.

But in 10 billion years, the universe has expanded so that star is actually, I don't know, about 50 billion light years away now. In the beginning, the star and photon are leaving each other at C but as the distance increases the space between them expands. and THAT makes them separate at a distance greater than C. But the image we see is a 10 billion year old image and we have no idea what that star is like in our time, today, at a distance of 50 billion light years.

We know that C is the limit in our accelerators, we push particles to that limit everyday and they will not go faster, just get heavier.

The photons are limited to C but spacetime is not. Spacetime is the medium that photon travels through.

Does that make sense?

And for my sake, please do not increase gravity. I have an hard enough time as it is! Now, if you could lessen gravity without losing the oxygen, I could support that!

I can give you some rough figures for that:

The CMBR was emitted 13.7 billion years ago.
The particles that emitted the radiation were 40 million light years away.
The photons travelled 13.7 billion light years to get here.
The particles are now 46 billion light years away.
The CMBR was emitted at 380,000 years, redshift z=1100 (some one can probably tell us the recessional velocity for z=1100).
Expansion exceeds c at high enough redshift. (I don't know the figure.)

I think if you travel close to c your mass appears to increase to an observer (thats true at least for time and length, which seem normal to you but shorter and slower to an observer).

When my wife flies on the Enterprise I'm always careful when she texts "does my bum look big in this?"

__________________
If something is in me which can be called religious then it is the unbounded admiration for the structure of the world so far as our science can reveal it... of the manifestations of the profoundest reason and the most radiant beauty, which are only accessible to our reason in their most elementary forms...
Albert Einstein

Steve, a friendly hint for you and any other male,

A woman does not need to be on the Enterprise for you to be careful when answering the "bum" question.

Noted.

Thanks Clegrand.

__________________
If something is in me which can be called religious then it is the unbounded admiration for the structure of the world so far as our science can reveal it... of the manifestations of the profoundest reason and the most radiant beauty, which are only accessible to our reason in their most elementary forms...
Albert Einstein

its more that that:

take what you said and re-write it a little:

"Say, 10 billion years ago, a supergiant star went supernova in the halo of a young galaxy and sends photons TOWARD that the Hubble Space Telescope WHICH ARE STILL BILLIONS OF LIGHT YEARS AWAY AND TRAVELING TOWARD US AT A SLOWER RATE THAN THE EXPANSION OF THE UNIVERSE so no focusing and no images today, tomorrow or ever."

"But in 10 billion years, the universe has expanded so that star is actually, I don't know, about 50 billion light years away now (or more like 500 billion light years) and not one photon as been able to rech us - not 10 billion years ago nor today nor tomorrow."

I enjoyed the back and forth. Can I try an experiment to see if I understand this?

I fire photon A toward anywhere, then a second later I fire photon B in the same direction. Over time, the time-interval between A and B actually is greater than one second, because the "space" between them is growing? That is, if A stopped, it would actually take more than a second for B to hit it. Relative to me, A is still travelling at the speed of light and so is B, neither is travelling faster than c.

Wow! That *is* some nice writing! Introducting the term metric and providing some background on that, really helps to understand the expansion of space better. I want to memorize this statement:

Superluminal space expansion

Because it is the actual metric that defines distance itself that is changing, rather than objects moving apart within space, this expansion (and the resultant movement apart of objects) is not restricted by the speed of light upper bound that results from special relativity.

Mine doesn't.

For some reason I have no problem visualizing it. It's just a fat version of the surface of a balloon, turned in on itself. (like a 4d doughnut)

its the drugs...

__________________
If something is in me which can be called religious then it is the unbounded admiration for the structure of the world so far as our science can reveal it... of the manifestations of the profoundest reason and the most radiant beauty, which are only accessible to our reason in their most elementary forms...
Albert Einstein