It is important to keep in mind that the bubble analogy is an analogy. The extra dimension is part of the model, not part of what is being modeled. If you take one (arbitrary) point as your origin, you will notice that everything is receding from the origin (along with some random noise motions, which I will ignore here). If you trance the vectors back, you will find that everything was once located at the origin at some time in the past, arbitrarily designated t=0. Where this point is in 4-space is not a meaningful question outside of the bubble model. The extra dimension has no real existence.
The bubble model can only be applied to a closed universe. The universe can only be traced back to a point for a closed universe. If the universe is open or flat, it is and always was infinite.
ftg, you are missing the point of the question entirely because you can’t get past your preconceptions.
Where did I say I was asking about the size of the universe in the Big Bang model? The question I’m asking relates to the justification for the Big Bang model itself. Simply assuming the Big Bang model is no justification at all.
I find it interesting that you berate using the measurements of the motion of galaxies, when it was precisely those measurements which lead to the conception of the Big Bang model in the first place.
And you know the space between them is getting smaller based on the measured “motion of galaxies in 3D”. But the question I’m still looking for an answer to is How much smaller do we know, based on measurements, the visible universe must have been without simply assuming it was zero?
So I apparently made an unforgivable mistake in thinking that ZenBeam was presuming the Big Bang. Pardon!
Let us classify galactic motion into three categories:
Motion within a galactic cluster. Us and Andromeda doing the dosey-do (see footnote) and such.
Motion between galactic clusters not related to expansion of the universe.
Motion between galactic clusters solely caused by expansion of the universe. (Important: I do not claim in any way that 2 and 3 can be separated via measurement.)
To the limits of our measurements, only for the closest galaxies do the first two dominate. For everything else the third dominates by far. Again, that is with respect to what we are capable of measuring. Consider each three and ZenBeam’s restatement (to be generous) of his original question.
Motion in a galactic cluster. Galactic clusters are the largest objects that are gravitationally bound. That is, they are presumed to be stable and will not get spread out over time.
Running the motions of a galactic cluster backwards in time means that they will not significantly contract.
Hence, this alone means that by measurement alone running the current state of the universe back in time it couldn’t get smaller than the largest galactic cluster. (Which isn’t ours. We’re the Fargo of clusters: 30 or so versus typically hundreds versus mammoths that are in the thousands.) This is a lower limit considering the first case alone.
Relative motion of galaxies unrelated to expansion. These vectors are all over the place, we could be heading way out beyond Virgo, another cluster might be heading towards a spot way out beyond Ursa Major. Etc. These will not converge in any nice way. Some pairs of clusters are in fact moving towards (and not away from) each other. This raises the lower limit from cluster size to universe size.
Relative motion of galaxies caused by expansion. From our naive point point of view, in 3d, these will always by definition point exactly to us. Hence exact measurement of this component will in no way help answer ZenBeam’s question. I know that certain people will think this is absurd but it’s quite true.
Wait. I’ve said this before. Pardon*2.
Re: DrMatrix’s points: All this is invariant on any of the flat/open/infinite/curved >,<,=1 etc. properties of the universe. It just assumes we are talking about a (perceptually) expanding universe.
ZenBeam’s more recent posts more directly relate to asking about measurable proof of the Big Bang theory. But only asking about galactic motion. We got a lot more measurements than just distance. Very important measurements.
Timeline:
1920’s Hubble discovers that redshift is proportional to distance. The universe seems to be expanding.
Cosmologists are baffled, initially.
1940’s Gamow proposes the Big Bang theory. This theory predicts that the universe should exhibit microwave black body radiation of a few degrees K.
1950’s Hoyle (most notably) goes to war against the Big Bang theory (his own disparging term!).
1965. Penzias and Wilson discover the Cosmic Microwave Background Radiation. Matches black body radiation of just under 3 degrees K. The stock of Big Bang theory skyrockets. A theory that predicts a strange property that is found years later by people not even looking for it has to be taken very seriously.
Note: It wasn’t Hubble’s measurements that made the Big Bang such a Big Bang of a theory, it was Penzias and Wilson. Nobel Prizes all around.
There are lots of sites around the web that provide the complete set of arguments for the Big Bang. If you want to debate the validity of the Big Bang, try Great Debates.
Whack-a-Mole’s orginal reply, with the correction, still stands.
Footnote: A group recently announced that Andromeda is heading towards the Milky Way and will eventually collide. Not yet accepted by many others. I.e., they could be wrong.
The CMBR dates from about 300,000 years after the Bang, so the universe certainly wasn’t a point then. The Boomerang results may push this back further, but I have no idea how far.
From Brian Greene’s The Elegant Universe, the measurement which depends on conditions earliest in the lifespan of the universe is the relative abundance of light elements produced during the first three minutes after the bang. The relative abundances of several light elements are predicted and agree with measured abundances, and would presumably vary if the universe’s size didn’t match the Big Bang model. Primordial nucleosynthesis couldn’t happen during the first 100th of a second, so this measurement doesn’t push back before then. This book predates Boomerang (2 years old, and it’s already out of date), so perhaps those measurements are relevant. I don’t know offhand how large the universe was at one 100th of a second. Plotting three points I knew, it looks like the size of the visible universe may go like T[sup]1.5[/sup]. If this is correct, the visible universe would be about a millimeter across at one 100th of a second.
I feel obligated to say something about the phrasing of the OP. I’m not sure why my OP implies the Big Bang model was an assumption. I made sure several times to indicate I was interested in measurements. I’m also not sure why asking how well one aspect of the Big Bang is verified by measurements belongs in Great Debates. I stand by the OP.
Finally, a disclaimer: While searching for Big Bang sites to help answer the OP, I searched on “Big Bang alternatives” and got a bunch of creationist websites. It hadn’t occurred to me they were anti big bang, but I guess it makes sense. I’m not a creationist, and I don’t have anything against the Big Bang model.
This surprises me. Not that the Pope is the final arbiter on all religions (or even any but Catholicism) but Stephen Hawking related a story about this in his book A Brief History of Time.
Hawking had a meeting with the Pope where the Pope told him that the work he was doing (looking into the creation of the Universe) was fine by the church but that he shouldn’t look into the moment of creation as that was God’s province. Hawking was a bit worried by this as he had either just or was just about to deliver a speech about how the early Universe was created and his findings really left no place for a God. Sharing a birthday with Galileo who was threatened with excommunication Hawking says he felt a worrisome kinship to that man.
Again, I’ll grant that the Pope isn’t the supreme official on all things religious but this story suggests that the Catholic Church, for one, is fine with the Big Bang. It is only the moment of creation (i.e. what set the Big Bang off) that they feel had to be under God’s supervision. The Universe then evolved from there based on physical laws that God laid down at the get-go.
We, here on Earth, make measurements of other galaxies. Using various methods, we find that in our reference frame, those galaxies are all moving. We are able to determine, to some degree of precision, the velocities with which those galaxies are moving. Based on extrapolations of those velocities, we can determine the positions of those galaxies at times future and past. At what time would those extrapolations be contained in the smallest possible volume, and what was that volume?
Let me know if I’ve missed anything there, ZenBeam. I still don’t know the answer, but I’ll keep looking. As to other matters brought up in this thread: An analogy of the Universe as a soap bubble is only really useful for a closed Universe, and even there, it’s got some major flaws. We’re sidestepping that whole issue by specifying a reference frame, namely our own from which we are making observations. In any given reference frame, you can talk about all of the galaxies moving away from a point.
COBE, BOOMERANG, MAP, and indeed any other observation limited to electromagnetic radiation has that same barrier at t=300,000 years. LISA-3 should be able to make gravitational-wave observations of the first second and earlier, but that’ll be a while yet: We’re worrying about LISA 1 and 2 first. And the leadership of the Catholic Church recently has been very friendly towards science in general, but there are a number of other sects or religions, or practicioners of any religion, who don’t share those views. In general, the same people who reject evolution also mostly reject the Big Bang, and often think that they’re the same thing.
I’d include the error bars on the velocity measurements, but that was pretty much the original question, and I’d still be interested in the answer.
As ftg pointed out, other measurements push the minimum size back, so the galactic velocity measurements are undercut by other measurements.
By the way, I found a table giving relative size of the universe as a function of time after the bang (Table 15.4 in Weinberg’s Gravitation and Cosmology). Assuming the current diameter of the visible universe is 30 billion light years, the values at about 0.01 seconds, 3 minutes and 380,000 years are:
R(0.0108) = R0 * 1.9E-11 = 0.57 Light Years
R(182) = R0 * 2.6E-9 = 78 Light Years
R(1.2E13) = R0 * 6.3E-4 = 1.9E7 Light Years
In my last post, where I said the size seemed to go like T[sup]1.5[/sup], that should have been T[sup]2/3[/sup], and so the 1 mm figure is seriously in error (it should have been more like 20 light-hours). It’s a moot point now, since I found the table of size Vs time for the relevent times.
One of the things BOOMERANG did was measure the angular variations of CMB. These variations arose prior to the t=300,000 year barrier, so they say something about the time prior to then. How far prior, and what they say, I don’t know. I was hoping someone else did.