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An Older, Larger Universe
Josh Fink writes "Space.com has a very interesting article as part their weekly mystery Monday series about a new calculation that shows that the Universe is actually much older than than the 14.3 billion years old that was established in 2003. From the article, "...the universe is instead about 15.8 billion years old and about 180 billion light-years wide." The calculations were based off of a recalculation of the Hubble Constant which dictates how fast the universe is expanding, and they found it is actually 15% slower than previously thought. The findings will be printed in an upcoming edition of Astrophysical Journal."
The expansion of space isn't governed by the speed of light.
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(from: http://www.space.com/scienceastronomy/mystery_mond ay_040524.html)
This article generated quite a few e-mails from readers who were perplexed or flat out could not believe the universe was just 13.7 billion years old yet 158 billion light-years wide. That suggests the speed of light has been exceeded, they argue. So SPACE.com asked Neil Cornish to explain further. Here is his response:
"The problem is that funny things happen in general relativity which appear to violate special relativity (nothing traveling faster than the speed of light and all that).
"Let's go back to Hubble's observation that distant galaxies appear to be moving away from us, and the more distant the galaxy, the faster it appears to move away. The constant of proportionality in that relationship is known as Hubble's constant.
"One seemingly paradoxical consequence of Hubble's observation is that galaxies sufficiently far away will be receding from us at a velocity faster than the speed of light. This distance is called the Hubble radius, and is commonly referred to as the horizon in analogy with a black hole horizon.
"In terms of special relativity, Hubble's law appears to be a paradox. But in general relativity we interpret the apparent recession as being due to space expanding (the old raisins in a rising fruit loaf analogy). The galaxies themselves are not moving through space (at least not very much), but the space itself is growing so they appear to be moving apart. There is nothing in special or general relativity to prevent this apparent velocity from exceeding the speed of light. No faster-than-light signals can be sent via this mechanism, and it does not lead to any paradoxes.
"Indeed, the WMAP data [on cosmic microwave background radiation] contain strong evidence that the very early universe underwent a period of accelerated expansion in which the distance been two points increased so quickly that light could not outrace the expansion so there was a true horizon -- in precise analogy with a black hole horizon. Indeed, the fluctuations we see in the CMB are thought to be generated by a process that is closely analogous to Hawking radiation from black holes.
"Even more amazing is the picture that emerges when you combine the WMAP data with [supernova] observations, which imply that the universe has started inflating again. If this is true, we have started to move away from the distant galaxies at a rate that is increasing, and in the future we will not be able to see as many galaxies as they will appear to be moving away from us faster than the speed of light (due to the expansion of space), so their light will not be able to reach us."
Wer mit Ungeheuern kämpft, mag zusehn, dass er nicht dabei zum Ungeheuer wird. --Nietzsche
This whole article is misleading. The new research has very little to do with our knowledge of the size and age of the universe.
(And, yes, I am an astronomer).
Stanek and company have used measurements of one eclipsing binary system to determine the distance to M33. This is a good way to measure distances, as it avoids the perils of even a short "ladder" of methods. They find a distance modulus of 24.92 +/- 0.12 mag to the binary. You can read their paper on astro-ph at
http://xxx.lanl.gov/abs/astro-ph?papernum=0606279
Go to Table 7 of their paper, in which they compare their distance to previous measurements. There are 12 previous values, measured by several techniques (only 2 of the papers use Cepheids). The range of those previous values is 24.32 +/- 0.45 to 24.86 +0.07/-0.11. Their new distance is inconsistent, at the 1-sigma level, with 6 of the 12 others; thus, it is consistent with 6 of the 12 others.
Yes, it's true that the HST Key Project distance to M33, computed using Cepheids, is smaller than the new distance by an amount well outside the quoted uncertainties. But that's not a big deal, by itself. M33 is only one of a number of galaxies which serves to calibrate secondary distance indicators, which may in turn be used to find the Hubble constant. A small change in the distance to M33, even if true, would not make any major change to H-nought.
Recall that M33 is close enough to us that its radial velocity is NOT caused by the expansion of the universe, but instead by the gravitational forces of the galaxies in the Local Group. The press release's statement
is absolute nonsense. One cannot USE the Hubble constant and radial velocity of M33 to calculate its distance. The radial velocity of M33 is -179 km/sec, so "using" the Hubble costant to determine its distance would yield a negative distance. Phht.
This is a very nice, and very very worthwhile scientific project -- I have followed the DIRECT team's efforts for years, and encourage them to keep going! -- but the press release tries too hard to make it into some sort of breakthrough with profound immediate results.
Sigh.
Michael Richmond "This is the heart that broke my finger."
mwrsps@rit.edu http://stupendous.rit.edu
I actually used to work on a team measuring the Hubble Constant using Radio Telescope data ten years ago - actually the same group who came up with 42 km s-1 Mpc-1 value which caused all the Douglas Adams H2G2 references (that was shortly before I joined). There was a lot of controversy over the value of the Constant back then and it is still a hot topic. Back then, the Hubble Constant was thought to have values anywhere from 30 km s-1 Mpc-1 up to 120 km s-1 Mpc-1 . The smaller the value of the Hubble Constant, the older the Universe is. Having a smaller value was desirable because it meant that the Universe was old enough to account for the oldest objects observed (about 16 billion years old). Think about that.
One of the points that struck me then was that the value of the Hubble Constant measured tended to be higher when measured using "more local" techniques and tended to be lower as techniques using more distant measurements were used. The Radio Telescope information gave us measurements based on object around or beyond a redshift of 1 (or, to put it another way, these clusters of galaxies observered were about half the age of the universe when the light left them).
Anyway, we'll be seeing more measurements of the Hubble Constant for many more years. Just remember the error bars!
Cheers,
Toby Haynes
Anything I post is strictly my own thoughts and doesn't necessarily have anything to do with the opinions of IBM.
I don't want to get flamed by saying people are asking dumb questions, but everyone just needs to stop relying on simple arithmetic when dealing with the size of space... The concepts involved are far more complicated than that.
One thing people don't seem to be grasping is that with the Big Bang model, the size of the universe isn't measured by the distance between two particles floating on the "edge". It is actually a measure of the width of the "fabric" of the known universe, space-time. Its difficult to grasp this since it is not something easily perceived.
The real reason for the size of the universe being so much larger is that the laws governing the size of space-time are not the same as the laws of spacial relativaty, and therefore are not constrained to the upper bound of the speed of light.
The best analogy that I've heard is the ant on the balloon example. The idea is that you picture an ant sitting on a balloon with a bread crumb an inch away. If you were to blow up the balloon to twice its size, the bread crumb wouldn't necessarily move to a distance of two inches from the ant.
In this example, we are the ants and we are watching the galaxies, represented by the bread crumb, moving away from us. However, the fabric of existence is expanding at a much larger rate.
The "what's beyond the edge" question is essentially a pointless question when dealing with space-time. There is no "edge" because nothing can possibly exist outside of the realm of spacetime.
And if that concept doesn't satisfy the question, then a simple-minded answer would be that an "edge" can never be reached as space-time is always expanding faster than any particle could possibly hope to keep up with it.
--
"A man is asked if he is wise or not. He replies that he is otherwise" ~Mao Zedong
Capitalism: When it uses the carrot, it's called democracy. When it uses the stick, it's called fascism.
There are several posts that mention that the universe can expand faster than light. They are right but let me see if I can expand on it some.
If you have taken a fair bit of math skip this and and go here http://pancake.uchicago.edu/~carroll/notes/ to Chapter 8 in particular.
We want the universe on the largest of scales to look isotropic and be homogeneous spatially. The first means it looks the same in all directions about some point, and the second meaning that its physical properties are the same everywhere. If the universe is isotropic about one point and it is homogeous it follows that it is isotropic about every point. Straight away there is no priveleged center and it is meaningless to talk about the center of the Big Bang or some such. Insert standard dots on a balloon or raisn bread rising explanation here but neither is perfect.
We can look at galaxies and can see spectral lines and can measure their shifts and recognize that they must be moving with respect to us, and are typically moving away from us so the univsere is expanding. So the universe must look the same from every point in space but it is not static and can look different at different times. Because we want to maintain homogeneity and isotropy through time and because we believe there are no privleged directions or points in space we want this expansion to be solely a function of time. This function of time is what is called the scale factor and it is the fundamental quantity that determines what present distances in the universe are and how fast they are changing. There is no speed of light anywhere around the scale factor, and there isn't going to be.
With all this we can write down the model for the universe, and its called the Friedmann-Lemaitre-Robertson-Walker metric after the smart people who came up with it. Thats fancy talk for a single line that tells you how to compute the "distance" between two events each occuring at their own space and time coordinates. Its equation 8.7 in the article. If you believe we live in a flat universe which you should because theres lots of good experimental evidence for it from studying the cosmic microwave background, even that simplifies a fair bit to something that can look like ds^2 = dt^2-a^2(t)(dx^2+dy^2+dz^2).
The second section in brackets to the right of the scale factor is the way you'd compute the distance between two events in 3d space, just the sum of the squares of their differences in position, and the dt^2 is the bit that adds on time. In any local region of the universe a(t) is constant and can be taken to be one and then you have a return to happy special relativity where the speed of light is constant to all inertial observers. Take a(t) to zero and you see the singularity in the equations which we call the Big Bang. This is where the model and the equations break down and thats all we can truly say about it. The universe (hopefully) does not break down, only our model to describe it does.
This metric, which we can write happily as a diagonal matrix even can be plugged into Einsteins equations and give you yet more equations like the Friedmann equation and the acceleration equation (Carroll 8.35 and 8.36), and you can derive Hubbles law and discusses all the interesting forms of matter you can have in it including what happens in Einstein's equation has a cosmological constant term. You'll notice theres still no speed of light. Stuff in the universe cannot move faster than the speed of light according to some local observer. However, the universe is sort of the fabric on which all the stuff is and that fabric can stretch faster than the speed of light. We do see object moving faster than light. See near end for an example, more information and no serious equations http://www.astro.ucla.edu/~wright/doppler.htm
Thats become somewhat important following the studies of distant supernovae from '98 and we now know that the univer
Reality must take precedence over public relations, for nature cannot be fooled.
The most simplest explanation is: Before the big bang, there was no space-time. The universe expanded into space-time and the space-time is expanding since then. Also just after the big-bang, the universe had an inflation where the inflation speed was much more than the speed of light. This smooths all of wrinkles of the the universe, hence the observable universe is homogeneous (everywhere laws of physics are the same).
The inflation theory is quite something - first time I read about it I didn't believe it but the evidence is pretty strong. On the other hand, mandkind don't know what was the governing principle. Same with the current increasing expansion of the universe, no one knows why (yet) but it expands faster and faster.
This was quite simplistic, probably also contain factual errors introduced with oversimplification. Wikipedia will have much more information and lots of links to more articles.
Also popular astronomy magazines (Sky&Telescope, Astronomy Now etc.) tend to have reasonably good cosmology articles once in a while.
expansion can be tricky to understand. OK, lets use your baloon analogy.
You take a balloon that's been partially inflated, and paint loads of evenly spaced dots all over it.
Then you further inflate the baloon. Each dot move away from each other dot at a uniform rate (well, more or less).
Universal expansion can be thought of in a similer fashion. It isn't that the edge of the universe is moving farther out, leaving just more and more space inside, it's that the 'space' between( for simplicities sake, galaxies), is increasing in size, expanding outward in every direction. Thus all the galaxies are moving away from each other in much the same way as the dots on the balloon.
Space is expanding like this everywhere, but in small uneven pockets of gravity such as clusters of galaxies, or inside a galaxy, the expansion is less obvious, because of gravity's effects.
The idea is that the planets are formed in a disc (a proto planetary disc). The disc itself forms from a cloud of dust and gas. They usually have some rotation. When the cloud collapses conservation of angular momentum spins up the collapsing cloud (think of skaters doing a pirouette, they start rotating faster), young stars rotate a lot faster than the cloud from which they formed. The shape of a cloud tends to a disk because of conservation of momentum and friction. The matter can move down to the disk by radiating away some of its potential energy through friction processes. The matter cannot move closer to the axis around which the system rotates because that is not compatible with conservation of momentum. So collapsing clouds don't just collapse into some central object but form a disk. In turn the planets form in the disk, that itself will evaporate when the star ignites its nuclear fusion. Planets formed in the disk are usually solid enough (heavy enough) to not get evaporated. Since the planets formed in the disk, they tend to lie in a plane. The planets store a lot of angular momentum.Orbits of planets can get perturbed by interactions among the planets or encounters with nearby stars.
This is roughly what astronomers think nowadays. The thing to remember is conservation of angular momentum. This is a really basic and important law that governs the formation of disks all over the universe (blackholes sucking in matter also form disks). Conservation of angular momentum is also why the moon moves away from earth (compensating for the slowing down of earths rotation around its own axis --- by moving the moon out the earth-moon system conserves angular momentum).
Sorry for the slightly rambling explanation, I'm sure wikipedia has more if your interested.
The fourth dimension could easily be physical. There's definitely a dimension we percieve as time. But just as we don't implicitly define what directions dimensions one, two and three are pointing, we don't say that time is always the fourth dimenion. It's just a cleaner explanation that way.
Oh, and if you're curious as to an "alternate" theory, there's some mindblowing stuff here: http://www.tenthdimension.com/flash2.php (Warning, contains Flash for you paranoids)