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harlequin
2004-May-18, 10:00 PM
You might think it is a long way to the chemist but that is just peanuts next to space....

The microwave background radation has used to show that the universe must be at least 78 billion light years across. Future observations from the WMAP probe might be able to push it to 90 billion light years across (assuming it is of course). Telescopes can currently see 28 billion light years away.

http://www.nature.com/nsu/040517/040517-3.html

Edit: Removed an error of fact on my part

Brady Yoon
2004-May-18, 11:08 PM
Does this mean that the universe expanded faster than light?

George
2004-May-18, 11:26 PM
Does this mean that the universe expanded faster than light?

Use the Hubble Constant (71km/sec per Mega parsec) to see at what point objects are at light speed.

Since acceleration (or is it jerk) is now a factor, this will change it some.

Sam5
2004-May-19, 01:23 AM
Does this mean that the universe expanded faster than light?

Of course it is!

Sam5
2004-May-19, 01:28 AM
Telescopes can currently see 28 billion light years away.



I think maybe that science writer means we are looking out in opposite directions along two radius lines of 14 bly each.

Normandy6644
2004-May-19, 02:35 AM
Telescopes can currently see 28 billion light years away.



I think maybe that science writer means we are looking out in opposite directions along two radius lines of 14 bly each.

I think you're probably right. otherwise, why would we not have tried to "look" that far back with telescopes? Makes more sense for it to just be double.

earthman2110
2004-May-19, 02:49 AM
so this has nothing to do with the proposed age of the universe, does it?? it is still 13.7 billion yearsish old? :-?

Sam5
2004-May-19, 03:05 AM
Normandy,

Do you recall when I said that I think the universe is “much bigger” than is currently believed?

I specifically said that my reason for believing this is because every time we built a bigger and sharper telescope, what do we see in the distance? More galaxies, with no end of them in sight.

And remember when I said that if the universe is actually much bigger than is currently thought, but if the current thinking is that it has a radius of only about 15 bly, then our viewing position seems to be “central”, since we see the “most distant galaxies” in all parts of the sky.

I also said that that is just an indication that we are in the center of our current “sphere of visibility”, but it doesn’t mean we are in the center of the universe, if the universe is much bigger than they think it is.

Ok, based on that article’s estimate of a maximum of maybe a 90 bly diameter (a 45 bly radius), this is were we could be, along the diameter line below, well off center, yet we would appear to be “in the center” if the astronomers have been under-estimating the true diameter of the universe. The circle represents us, the parentheses represent our 14 bly limit of visibility. The dashes represent 1 billion light years distance. The total length of the diameter line is 90 bly:

---(--------------o--------------)----------------------------------------------------------

Taibak
2004-May-19, 04:22 AM
Sam5: Actually, the full 78 billion light years hasn't been imaged and can't be imaged. No telescope can change that. The article is talking about a theoretical calculation based upon fluctuations within the cosmic microwave background. However, all those fluctuations are within 14 billion light years. We can't detect anything further away, because there hasn't been enough time for the signals to reach us. Even so, that 78 billion light years is a *minimum* size for the universe. The generally accepted theory still holds that the universe is infinitely large.

freddo
2004-May-19, 04:23 AM
Try this...


∞---------------------(---E---)--------------------------∞

E is Earth... We're in the centre of what we can see - and we can't see anything that looks more or less like the centre in any direction.

Lets go a couple of galaxies over and take a look from there...


∞---------------------(---ACOGO---)--------------------------∞

Oh dear. It seems that we're again in the centre of what we can see - and we can't see anything that looks more or less like the centre in any direction.

Perhaps there is no centre beyond one arbitrarily chosen by humans who can't imagine a universe without one?

Kullat Nunu
2004-May-19, 06:46 AM
What that 78 billion light years mean anyway? Things get really messy when you have to determine cosmological distances.

Take for example a galaxy that is said to be 10 billion light years away. It means that light left the galaxy 10 billion years ago. Then the galaxy was only a couple of billions light years away. Currently it is over ten times more distant.

Kullat Nunu
2004-May-19, 06:50 AM
...at least 78 billion light years across.

Note: at least. It may be (I'm sure it is) much, much bigger.

Sam5
2004-May-19, 11:23 AM
Perhaps there is no centre beyond one arbitrarily chosen by humans who can't imagine a universe without one?

Hi Freddo,

An “infinite” universe is not consistent with a universe that is supposed to be only “14-15 billion years old”. This would mean that most of the galaxies in it traveled through space at an “infinite” speed, and I don’t think there are any known laws of physics that allow that.

Also, if it’s already “infinite”, it can’t be “expanding” because it’s already “infinite”. Also, it can’t “expand” from zero to “infinite” in 14-15 billion years with the restriction of a “c” speed limit applying to the motion of the galaxies.

My guess is that it has some large diameter and is also expanding, and that the current estimate of about 28 bly diameter is just a current misjudgment.

Astronomers have been wrong before, like with all that stuff about the “green plants growing on the surface of Mars” that astronomy textbooks taught American students back in the ‘50s.

Sam5
2004-May-19, 11:27 AM
The generally accepted theory still holds that the universe is infinitely large.

That is not the “generally accepted theory”. That might be your favorite theory. Would you like to tell me how fast the “infinitely distant” galaxies had to travel to get an “infinite distance” from us in 14 billion years? And what happened to the “speed limit of c”?

Kullat Nunu
2004-May-19, 11:57 AM
Also, if it’s already “infinite”, it can’t be “expanding” because it’s already “infinite”. Also, it can’t “expand” from zero to “infinite” in 14-15 billion years with the restriction of a “c” speed limit applying to the motion of the galaxies.

I think you have misunderstood.

Yeah, there is speed limit of c but it applies only to information (and thus to light and so on).

Let's take an example: You walk in front of a searchlight; how fast your shadow travels at the distance of the Moon? Jupiter? Distant galaxy? In theory the light from the searchlight is visible even there, it's just very dim. How fast your shadow travels there? Billions of times faster than light. No problem, no information is transmitted.

Similarly, universe can be much larger in diameter than 28 billion light years. During inflation -- if that happened, evidence is quite good -- the universe expanded much faster than the light. Again, no information transmitted. Similarly very distant galaxies can recede at superluminal speeds.

On the other hand, it may be so that the Big Bang didn't happen in a infinitesimal point but everywhere in space at once (carefully here, if the universe was a point *it* was the whole space). Ekpyrotic (sp?) model suggests so.

And finally, of course infinite can expand. Take for example the set of natural numbers {1,2,3,...} and add halves between the numbers {1,½,1½,2,2½,3,...}. Infinity just expanded (although its cardinality didn't change, its still infinite).

Sam5
2004-May-19, 12:44 PM
Similarly, universe can be much larger in diameter than 28 billion light years. During inflation -- if that happened, evidence is quite good -- the universe expanded much faster than the light. Again, no information transmitted. Similarly very distant galaxies can recede at superluminal speeds.

I've been saying that for years.




And finally, of course infinite can expand. Take for example the set of natural numbers {1,2,3,...} and add halves between the numbers {1,½,1½,2,2½,3,...}. Infinity just expanded (although its cardinality didn't change, its still infinite).


That doesn’t “expand infinity”, that divides infinity into an infinite number of 1/2 increments instead of using an infinite number of whole increments.

Don’t stop at 3. Go ahead and carry your numbers on out to the end. I’d like to see how big an infinite number of numbers is.

John Kierein
2004-May-19, 01:08 PM
Also, if it’s already “infinite”, it can’t be “expanding” because it’s already “infinite”. Also, it can’t “expand” from zero to “infinite” in 14-15 billion years with the restriction of a “c” speed limit applying to the motion of the galaxies.

I think you have misunderstood.

Yeah, there is speed limit of c but it applies only to information (and thus to light and so on).

Let's take an example: You walk in front of a searchlight; how fast your shadow travels at the distance of the Moon? Jupiter? Distant galaxy? In theory the light from the searchlight is visible even there, it's just very dim. How fast your shadow travels there? Billions of times faster than light. No problem, no information is transmitted.

Similarly, universe can be much larger in diameter than 28 billion light years. During inflation -- if that happened, evidence is quite good -- the universe expanded much faster than the light. Again, no information transmitted. Similarly very distant galaxies can recede at superluminal speeds.

On the other hand, it may be so that the Big Bang didn't happen in a infinitesimal point but everywhere in space at once (carefully here, if the universe was a point *it* was the whole space). Ekpyrotic (sp?) model suggests so.

And finally, of course infinite can expand. Take for example the set of natural numbers {1,2,3,...} and add halves between the numbers {1,½,1½,2,2½,3,...}. Infinity just expanded (although its cardinality didn't change, its still infinite).

Sorry, shadows travel at c and information is transmitted.

Kullat Nunu
2004-May-19, 01:49 PM
Sorry, shadows travel at c and information is transmitted.

Does it?

I don't mean radial distance, of course shadow comes with light.

Think about geometry: if it takes a second to walk across the light, shadow is visible a second too. Let's presume that the light is visible at angle of 45 degrees. At distance of a million km it takes one second to travel about 830 000 kms, that is almost 2.8c if I got it right. And other end have no idea what is happening at the other (until light has traveled there), they just see the light dimming as the shadow passes that point.

Kullat Nunu
2004-May-19, 02:03 PM
And finally, of course infinite can expand. Take for example the set of natural numbers {1,2,3,...} and add halves between the numbers {1,½,1½,2,2½,3,...}. Infinity just expanded (although its cardinality didn't change, its still infinite).

That doesn’t “expand infinity”, that divides infinity into an infinite number of 1/2 increments instead of using an infinite number of whole increments.

It divides nothing. Think the numbers {1,2,3,...} as evenly distributed points in space. In case {1,1½,2,2½,3,...} the space has expanded twice its original size. No expansion? Of course infinity distant lies still at infinity i.e. in such case there is no most distant place. If you meant that, we were speaking of different things.


Don’t stop at 3. Go ahead and carry your numbers on out to the end. I’d like to see how big an infinite number of numbers is.

Why should I? If I added every ½ simultaneously, infinity would be not a problem.

George
2004-May-19, 02:10 PM
The inflation seems to play a key role, right?


One of the peculiarities of inflation is that it seems to take place faster than the speed of light. Even light takes 30 billionths of a second (3 x 10(exp-10) sec) to cross a single centimetre, and yet inflation expands the Universe from a size much smaller than a proton to 10 cm across in only 15 x 10(exp-33) sec. This is possible because it is spacetime itself that is expanding, carrying matter along for the ride; nothing is moving through spacetime faster than light, either during inflation or ever since.

I've seen various sizes. I think 10 cm is on the small side.

In this scenario, space expansion is about 20 billion trillion times the speed of light. (Hyper light speed?). If this estimate is short a billionth of a second, then the 10cm size becomes about 700,000 light years and that's if the rate of expansion I used is accurate!

So, is it not plausible the total universe (not just the observable) could be much larger. Issues such as recombination and the flatness of the universe would still be valid as aren't these really density issues? Is there any stumbling block to a much larger universe?

Normandy6644
2004-May-19, 03:14 PM
Normandy,

Do you recall when I said that I think the universe is “much bigger” than is currently believed?

I specifically said that my reason for believing this is because every time we built a bigger and sharper telescope, what do we see in the distance? More galaxies, with no end of them in sight.

True, but we have been able to see the different stages in galactic evolution, so to speak. No one has yet used a telescope to see into the "cosmic dark ages" yet, and if they did, they probably wouldn't see much. Of course if they did, it would be quite interesting....


And remember when I said that if the universe is actually much bigger than is currently thought, but if the current thinking is that it has a radius of only about 15 bly, then our viewing position seems to be “central”, since we see the “most distant galaxies” in all parts of the sky.

Right.


I also said that that is just an indication that we are in the center of our current “sphere of visibility”, but it doesn’t mean we are in the center of the universe, if the universe is much bigger than they think it is.

Right, i'll go with that.


Ok, based on that article’s estimate of a maximum of maybe a 90 bly diameter (a 45 bly radius), this is were we could be, along the diameter line below, well off center, yet we would appear to be “in the center” if the astronomers have been under-estimating the true diameter of the universe. The circle represents us, the parentheses represent our 14 bly limit of visibility. The dashes represent 1 billion light years distance. The total length of the diameter line is 90 bly:

---(--------------o--------------)----------------------------------------------------------

Yeah, this all seems fine. I'm not sure how you would go about proving any of it, since all observations would inherently be biased to our "sphere of visibility," but theoretically I don't think there is much of a problem with this. Maybe I haven't thought about it hard enough though. :wink:

Taibak
2004-May-19, 03:44 PM
The generally accepted theory still holds that the universe is infinitely large.

That is not the “generally accepted theory”. That might be your favorite theory. Would you like to tell me how fast the “infinitely distant” galaxies had to travel to get an “infinite distance” from us in 14 billion years? And what happened to the “speed limit of c”?

They formed there.

TravisM
2004-May-19, 05:04 PM
Time, being a dimension in minkowski's space-time, needs to be brought up. Time doesn't have to be linear and you can play with time variables a bunch, it being realative to the motion of the observer and observed in relation to an arbitrary motionless origin.
The inflationary epic of the universe happened much, much faster than the speed of light, but that' assuming that 10^-30 seconds was 10^-30 during that time. I hate temporal mechanics...
Time may not march to just any drummer, but if it does that drummer may just be warming up...

ToSeek
2004-May-24, 04:27 PM
Mainstream article (http://www.space.com/scienceastronomy/mystery_monday_040524.html) from space.com.

earthman2110
2004-May-24, 04:51 PM
ok, im really really sorry, but can someone tell me if my small brain really understands this?

we can "see" 13.7 billion light years away. so that photon that started toward us at the edge of the visible universe started 13.7 billion years ago. since that photon started, the universe has expanded to 156 billion light years wide? is that whats going on here, or am i missing something?

TheGalaxyTrio
2004-May-24, 04:53 PM
This seems to assume that the photons in the beam of light are travelling at infinite velocity.

If you sweep a beam of light in a circle, you don't get a solid rod of light with an endpoint twirling around at superluminal speeds.

What you get is an expanding sprial of photons.

ToSeek
2004-May-24, 05:04 PM
we can "see" 13.7 billion light years away. so that photon that started toward us at the edge of the visible universe started 13.7 billion years ago. since that photon started, the universe has expanded to 156 billion light years wide? is that whats going on here, or am i missing something?

Well, we can't actually see 13.7 billion light years away (more like 13 billion even), but other than that you seem to have the right idea.

As I understand it, the expansion of space itself is not limited by the speed of light.

ToSeek
2004-May-24, 05:06 PM
This seems to assume that the photons in the beam of light are travelling at infinite velocity.

If you sweep a beam of light in a circle, you don't get a solid rod of light with an endpoint twirling around at superluminal speeds.

What you get is an expanding sprial of photons.

Even so, if you quickly turn the flashlight 180 degrees, you'll end up with an effective velocity for the end of the light beam of 2c.

NubiWan
2004-May-24, 05:31 PM
Ummm..., let's see, "sprang forth from an infinitely dense point...," "radius, diameter," "It can be thought of as a spherical diameter in the usual sense," ",..the universe is almost surely flat, not spherical. The flatness refers to its geometry being "normal..," spheres do have centers, then dang it !!! Being unable to locate it for the above mentioned reasons, is not the same as there not being one... #-o
This measurement does not prove the universe is infinite, nor does it rule out the possiblity that it may be, me tinks..., just sets the 'lower limit' of its size, huh?

Kullat Nunu
2004-May-24, 06:41 PM
Ummm..., let's see, "sprang forth from an infinitely dense point...," "radius, diameter," "It can be thought of as a spherical diameter in the usual sense," ",..the universe is almost surely flat, not spherical. The flatness refers to its geometry being "normal..," spheres do have centers, then dang it !!! Being unable to locate it for the above mentioned reasons, is not the same as there not being one... #-o
This measurement does not prove the universe is infinite, nor does it rule out the possiblity that it may be, me tinks..., just sets the 'lower limit' of its size, huh?

When cosmologists speak about spherical universe, they mean positive curvature, 3-D universe being like the surface of a 4-D sphere, and it of course does not have center. (That doesn't mean we need a fourth spatial dimension.)

Flat universe means "normal" space to which we are used to.

Don't mind, I don't understand it really either... :)

Sam5
2004-May-24, 10:52 PM
we can "see" 13.7 billion light years away. so that photon that started toward us at the edge of the visible universe started 13.7 billion years ago. since that photon started, the universe has expanded to 156 billion light years wide? is that whats going on here, or am i missing something?

A professional astronomer on the board said the light from that galaxy actually started out when the galaxy was only about 2 billion light years away from the earth.

Davis and Lineweaver said that the reason it took so long for the photons to reach us from the superluminal galaxy is because during the first couple of billion years the photons were traveling backwards, moving away from the earth, with their speed being regulated by the “comoving space” of the distant galaxy and other galaxies near it. As the photons got further and further away from that galaxy, they began to speed up relative to the earth and we finally see them traveling at c relative to the earth.

Sam5
2004-May-24, 10:55 PM
When cosmologists speak about spherical universe, they mean positive curvature, 3-D universe being like the surface of a 4-D sphere, and it of course does not have center. (That doesn't mean we need a fourth spatial dimension.)


This is pretty much double-talk and baloney.

ToSeek
2004-May-25, 01:55 AM
When cosmologists speak about spherical universe, they mean positive curvature, 3-D universe being like the surface of a 4-D sphere, and it of course does not have center. (That doesn't mean we need a fourth spatial dimension.)


This is pretty much double-talk and baloney.

For those of us who have taken the time and trouble to study non-Euclidean geometry, it makes perfect sense. I would suggest that you do likewise before dismissing statements you don't understand as "double-talk and baloney."

Cougar
2004-May-25, 03:19 AM
...so that photon that started toward us at the edge of the visible universe started 13.7 billion years ago. since that photon started, the universe has expanded to 156 billion light years wide? is that whats going on here, or am i missing something?
Yeah, it's very odd trying to visualize this. Redshift analysis tells us the photon has been traveling for 13.7 billion years. But since it's traveling through an expanding medium, when it started its journey, it was a lot closer than 13.7 lightyears. And now that it has arrived here, its starting point is a lot further away than 13.7 lightyears.

Plus, I think there's some ambiguity in the definition of "lightyear." Traditionally it is defined simply as "the distance light travels in one year." But wait a minute. Since all space in this universe is expanding, when it finally arrives, its starting point is farther than one light year away. So I guess a true lightyear is the distance light travels in a year minus the extra distance caused by the expansion of space. (?) That's a heck of a way to define a distance. :-k

eburacum45
2004-May-25, 04:06 AM
The clearest explanation of this I am aware of can be found here;

http://anzwers.org/free/universe/redshift.html

Basically the most distant galaxies of the observable universe are accelerating away from us while emitting light waves towards us; the light has taken 13 billion years or so to get here, but in that time the galaxies have moved much further away.

AZgazer
2004-May-25, 04:57 AM
In the space.com article it was stated that we can can look 90% back into the past. How is this gauged? and what is the accuracy of the method?


(Edit for clarity.)

RBG
2004-May-25, 06:07 AM
This seems to assume that the photons in the beam of light are travelling at infinite velocity.

If you sweep a beam of light in a circle, you don't get a solid rod of light with an endpoint twirling around at superluminal speeds.

What you get is an expanding sprial of photons.

Even so, if you quickly turn the flashlight 180 degrees, you'll end up with an effective velocity for the end of the light beam of 2c.


[-( No, this can't be right. (Disclaimer: What the heck do I know?) I'm sure that last statement falls in the same category as " I can look across millions of light years in the night sky in about a second so this must prove things go faster than the speed of light."

RBG

eburacum45
2004-May-25, 06:49 AM
Sweeping a superpowerful light beam around the heavens is a well known thought experiment; the end of the beam travels faster than light, but can't be used to transfer information between two remote locates at ftl speeds.

A thought experiment?

No!

Hubble's Variable nebula has a bright star at one end, which is surrounded by broken clouds; the slower-than-light movements of the clouds show up as shadows in the nebula nearby;
http://www.umanitoba.ca/faculties/science/astronomy/cbrown/imaging/hvn/shadowtransit.html

these shadows themselves often move faster than light!

George
2004-May-25, 12:15 PM
Hubble's Variable nebula has a bright star at one end, which is surrounded by broken clouds; the slower-than-light movements of the clouds show up as shadows in the nebula nearby;
http://www.umanitoba.ca/faculties/science/astronomy/cbrown/imaging/hvn/shadowtransit.html

these shadows themselves often move faster than light!

8) . Very interesting. Of course, a shadow isn't a "thing" moving faster than light and if we were located near the nebulae, we would not be able to see it move faster than light. (I think).