Follow Slashdot blog updates by subscribing to our blog RSS feed

 


Forgot your password?
Close
typodupeerror
×
Science

Age of Universe Derived 182

Posted by Hemos from the that-makes-sense dept.
HaeMaker writes "The age of the universe has been calculated to be 12 Billion years +/- 10%, and the Hubble Constant (the rate at which the universe is expanding), is 70km/s/Mparsec.... or in other words, for every Megaparsec (3.26 Billion Light Years) an object is away from us it is moving 70km/s away from us. So, if a galaxy is 2 megaparsecs away, it is moving at a speed of 140km/s away from us. Here is NASA on the subject. "
This discussion has been archived. No new comments can be posted.

Age of Universe Derived More

Age of Universe Derived

Comments Filter:

  • When people talk about the edge of the universe (and sometimes qualify it by saying 'observable universe'), they are referring to the 'shell' from which a photon of light, if it started travelling at the start of the universe, would have just reached us. In essence, it provides a limit to what we can see or be affected by

    If you travel indefinitely in one particular direction, then you will obviously not meet the edge, since (naively) to stop it 'pulling away' you must travel at the speed of light (Since that is the speed at which it is receeding)

    If I recall, space (if closed) can be thought of as an expanding 4D hypersphere

  • I heard recently about theories concerning
    'tension' of space -- and indications that,
    to some degree, Einstein was right to add
    the cosmological constant.
  • Every point in Universe is the former center of Universe.
  • This debate is not over by a long shot. Hubble's resolution ability is too inferior to accurately gauge h0. Since they have been surveying many distant galaxies using many different techniques to determine their distances, one slight mistake in assumptions could throw their calculations off. In next months American Astronomical Journal there will be research results printed from SN1998b which gauged H0 to be 64 m/sec/Mpc. Although this still gives the age of the universe as being around 12 billion years old, it should lay to rest this argument. The technique of using Cepheid variables and a Supernova type Ia in the cosmological distance ladder is agreed by everyone in the astro community as being the most reliable method of determining the Universe's age. I'm putting a paper online within the next couple of days if anyone is interested in reading it. Email kevlar@mail-me.com for more information.

    ~~Kev
  • Did they mention anything about the dark matter/"missing mass" question in the article? (I couldn't get to the NASA website; must be the famed /. Effect.) Regardless, I was thinking about that very question the other night and this is what I came up with:

    1. The astronomers/cosmologists say they can't find the amount of mass in the universe that theory predicts.
    2. Some have proposed "dark matter" which can't be seen. This could be something exotic and science-fictiony, or could be merely hundreds of small asteroids floating in interstellar space, or massive black holes...

    But think for a second: There is a universal "background radiation" everywhere you look in the universe, as empty space has a temp. of about 3 K. (There's energy everywhere, in other words.) Now everybody knows E=mc^2, so it's easy to see that m=E/c^2. Photons have zero rest mass, but they're never at rest, and so have a little tiny bit of mass...

    Empty space radiating at 3 K doesn't correspond to a lot of energy, of course, but there's a heck of a lot of space out there, all of it with some energy, and hence with some mass. Could that be where the "dark matter" has gotten to?

    (Yeah, I know this is slightly off-topic, but I thought it might be of interest. My physics is probably completely screwed up, too...)

  • So if when the radius of the universe increases by a factor of two, the total area of the universe increases by a factor of 4, what is the mass of the universe? Can we calculate this?
  • Even though the universe is expanding (according to theory), as a whole it is stationary w.r.t. itself, so it does make sense to ask the question "how old is it?"

    I think.

    g
  • Here's some links to check out:

    sci.astro Cosmology FAQ [astronomy.net]
    Ned Wright's Cosmology Tutorial [ucla.edu]

    The above question is discussed, among other things.
  • I'm not too good at physics anymore. Does this new info mean that the universe is expanding at a rate fast enough to counteract gravity (expanding forever)? Or is it not fast enough, and will eventually collapse upon itself again? I had seen some calculations a while back that said it was expanding forever, but now that there's apparently new info, has the situation changed (well, at least our perception of it)??

    Thanks in advance to anybody who knows...

    -----BEGIN ANNOYING SIG BLOCK-----
    Evan

  • The last part of the first paragraph should read open, Omega 1.

    (When will I learn to use the preview button?)

  • Several current theories hold that the universe expanded for a bit at less than light speed, then underwent superluminal expansion (inflation) objects at the 'edges' of the universe lost contact. This is based on the fact that objects whose light is just reaching Earth from opposite directions are similar in nature even though neither object can yet 'see' the other. They MUST have been able to see each other in the past in order to be uniform.

    In some of those models ('Cosmic Foam'), some parts are still experiancing inflation but we cannot see them (since they are moving away from us faster than light).

    Personal musings: Interestingly, under that theory, to leave our local (but very large) bubble where inflation is done, would be like entering the event horizon of a black hole. It is a one way trip because you are now receeding from that boundary faster than light. For the same reason, you have disappeared from the perspective of an observer inside the bubble.

    Scientific American had several good articles on all of this 2 or 3 issues ago.

  • Slight error in post. (Score:5)

    by Gruuk ( 18480 ) on Wednesday May 26, 1999 @03:02AM (#1879340)
    Just a small correction: a megaparsec is 3.26 million light years, not 3.26 billion.
  • Responding to those parts of your comment that I can actually parse: Quasars are very distant. Any determination of their age will require using H_0. That's what the Key Project has made a measurement of. It makes no sense to say that the new measurement of H_0 is wrong because computations using it produce results inconsistent with a different value of H_0, but that's what you're doing. Now, it makes more sense to estimate the age of something nearby, which you can do without using H_0, thereby getting a lower bound on the age of the universe in a way independent of cosmological parameters. The classic way to do this is isochrone fitting of globular clusters. You look at a GC near our galaxy, and use stellar models to determine the GC's age based on which stars are still around (massive, bluer, more luminous stars die earlier). Now, first, these methods used to give much different answers, with age(GC) considerably larger than age(Universe). That's bad. But more recent determinations of most quantities typically allow age(GC) age(Universe), with some time for GC's to form, within the errorbars. Putting that aside, there are a few problems with this method anyway: 1) It's been written here at least twice, and I'll make it a third. The HST H_0 Key Project did not measure the age of the universe. They measured H_0. To get t_0, you also need other cosmological parameters. And the difference between t_0 for an empty universe and a flat universe for a given H_0 is considerable, 50%! 2) If your stellar models are wrong, your isochrones that you use to fit GC stellar populations are wrong. Why assume that the GC method is right, and the measurements of H_0 and other parameters are wrong? Hell, they're probably all wrong! Anyway, may I suggest that you drop the flamebait and consider the possibility that the folks who have devoted their life to this science might have an edge over you in this matter? It's pretty presumptuous to stand up and declare work to be wrong when you hardly know anything about it.

  • I didn't mean to imply that the reasearchers didn't know what they were talking about. What I meant was that because of all the uncertainty in these kinds of calculations..any result should be taken with a grain of salt. At least until all of the variables can be explained and justified 100%.
    No one is arguing about Newtons Laws anymore because they have been proven correct. The formulas and constants used in the universal expansion and age calculations still have a long way to go.

    Ex-Nt-User

    Ex-Nt-User
  • Maybe there is something 13 billion
    light years away that won't be seen
    till next year.

  • Take it with a grain of salt.. (Score:4)

    by Ex-NT-User ( 1951 ) on Wednesday May 26, 1999 @03:19AM (#1879347) Homepage

    It seems that every few years some new group of researchers "discovers/calculates" the age of the universe. And everytime they recalculate it the universe seems to get older by a few billion years. So I would take this latest calculation with a grain of salt, 'cause I'm certain that in a few more years someone is gona claim that it's 13+ billion years old.

    Ex-Nt-User
  • Is there? What is the absolute smallest thing you can think of? Long ago it was likely a piece of dirt. Then maybe an amoeba, an atom, an electron. What is it now? A neutrino? Have you seen inside one to know that it's the smallest particle? Prove to me that there is a limit to how small something can be and I'll be perfectly happy to rescind my theory.
  • The new results agree with what we knew before, they're just more precise. So now it looks like we're definitely in for permanent expansion.

    The biggest question remaining is just how fast that expansion will be in the future - slowing down or speeding up? This depends on the value of the cosmological constant, a value which is highly contested right now.

  • Re:Age of universe (Score:2)

    by Anonymous Coward
    In the most common cosmological models, space does not have an edge. It is either infinite in extent (picture a plane) or finite but unbounded (picture the surface of a sphere, you can travel across the surface without ever running off the "edge"). (Of course, space is the 3D analogue of these 2D examples.)
  • Does anyone know if all these old objects are observed in one area of the sky?

    They are everywhere. Some of them are quite nearby, in fact. There are globular clusters orbiting the Milky Way that are thought to be about 12 gigayears old. That was one of the problems with the previous estimates - there were globs that were older than the universe according to the estimates. I think the new age estimates are more in line.

    My logic would tell me that we are seeing them now at the location where they were x billion years ago. And if we are seeing them as they were shortly after the BB, shouldn't they be fairly closely packed?

    Not sure why you think this should be so. If two distant objects were on opposite 'sides' of the universe (from our point of view) when light left them 12 billion years ago, wouldn't they still appear to be on opposite sides of the universe today? In any case, I think they are distributed pretty uniformly.

    g
  • A better analogy is a ball of bread dough with raisins in it (mmmm.. cinnimon raisin :)

    anyway... as the bread cooks, it expands, carrying the raisins away from each other (each raisin moves away from every other raisin)

    But the raisins themselves don't expand (like a dot on a balloon would) they simply get carried into the new space, like galaxies and clusters of galaxies.

    if you think of three raisins, one near the center, one half way out, and one on the edge, you see how hubble's constant works.

    The inner raisin sees the middle one (1 distance unit away) moving by however much the dough between them expands (say 1 velocity unit), then the outer one by say 2 velocity units (at 2 distance units away).

    Then you would have hubble's constant of 1 velocity unit per 1 distance unit. To put it in terms of actual units, 1 km/s per 1 Mpc.

    Now think in terms of the middle or outer raisin. The middle raisin sees each of the other two raisins moving away from it at 1 velocity unit, and they are each 1 distance unit away. So the middle raisin measures the same value for hubble's constant! (same for the outer raisin).

    Thus it doesn't matter where we are in the universe when measuring hubble's constant.

    Doug
  • First, the universe doesn't have an area, it has a volume. Three dimensions and all that. So if its radius goes up by a factor of two, the volume goes up by a factor of eight.

    One of the important cosmological parameters, Omega (in its various subtypes, such as "Omega mass", "Omega baryonic", "Omega lambda" (the cosmological constant), "Total Omega") is essentially a measure of the density of the universe.
  • You 32-bit luddites and your prophecies of doom.

    Go 64 bits. A LITTLE more time to think.
  • Here's a couple of cool ways of looking at this:

    1. Where are we? Are we at the "edge"? The "center"? Since all galaxies (except a couple of nearby ones) are moving away from us, maybe we're at the center. Maybe it's like the old "spots on a balloon" example: to each spot on an expanding balloon, everyone is moving away.

    2. Let's say we're at the center. The age of the Universe is 12 billion years. That means we can see 12 billion light-years in all directions, which we take as the "edge". Let's say we travel at the speed of light so we can reach the edge as fast as possible. Once we go 12 billion light-years, we stop and look around. Whoops! It's been 12 billion years! The "edge" has moved! The Universe is much bigger now.

    3. Let's say we're at the center again. We can see 12 billion light-years in all directions. However, the light from the "edge" is 12 billion years old, the age of the Universe. We're seeing the hydrogen from the Big Bang, the center of it all, in all directions. Does this mean that the "edge" is actually the original center of all things?

    Fun with cosmology.
  • As an xhausmate would say, kinda sorta not really.

    The problem is that _everything_ used to be in the center of the universe --- that's, by definition, what it means for the universe to be expanding. So, from the point of view of all points in the universe, it looks like the rest of the universe is accelerating away ... IOW, the distance between points of interest is getting greater.

    So everyone thinks they used to be the center of the universe, and they're right.
  • Use the (admittedly overused) expanding balloon example. You're on a balloon, on the surface. Someone starst blowing up the balloon. All the other points on the balloon start moving away from you. The points right next to you are moving away from you slowly, but the point on the far side of the balloon are moving away really fast (as fast as the diameter is growing). The universe is something like that (only a tad bit more complicated) So yeah, it actually is moving away from you. And yes, there is a doppler shift.

    Then again, every time I mention anything related to physics on slashdot, I'm wrong, so who knows.

  • Re:Age of universe (Score:3)

    by GrenDel Fuego ( 2558 ) on Wednesday May 26, 1999 @03:25AM (#1879369)
    Has anyone ever wondered what's at the edge of the universe?

    Socks. A whole lot of non-matching socks..
    And pens.

    And.. uhm... Jimmy Hoffa.

  • Star Wars part of our universe? (Score:3)

    by William Wallace ( 18863 ) on Wednesday May 26, 1999 @03:20AM (#1879370)
    Here's a quote from the article (no joke):

    "Alternatively, the universe is pervaded by a mysterious 'dark force' pushing the galaxies farther apart, in which case the Hubble measurements point to an even older universe."

    Damn that Darth Vader...


  • Is stuff that's further away actually going faster, or is it doppler/red shifting? or, to us mere mortals would it appear to go even faster?

  • The Hubble Constant and Ideology (Score:3)

    by Aravaipa ( 30801 ) on Wednesday May 26, 1999 @05:35AM (#1879372)
    It is quite interesting how this long and rancourous debate over the Hubble constant highlights the still non-zero tendency of ideology to intrude into science. For many years their were two main camps of astronomers working on this problem. One camp invariably found a value of around 50 km/s/Mpc while the other group always seemed to come up with 100 km/s/Mpc. The real howler was in the uncertainties which were usually quoted as +/- 5 or so. It doesn't take a supergenius to realize that something was not quite right here. Thankfully, this somewhat embarrassing rift in astronomy history appears to be closing due to the featured work of a third group headed by Wendy Freedman. Eventually science self-corrects for ideology, and therein lies the secret for its progress.

    Probably the most amusing aspect of this history is that for all these years the number quoted in the textbooks was usually 75km/s/Mpc. Not because a large number of measurements yielded this value, but because it represented a compromise between the 50 and 100 camps. Turns out that number wasn't far off after all!
  • A current theory is that certain types of neutrinos do posses a fraction of mass, which is used to explain this discrepancy. There are a few neutrino observatories buried deep in mine shafts that have apparently confirmed that these neutrinos do indeed have slight mass. This would explain the missing mass in the universe.
  • Comment removed based on user account deletion
  • There is a flaw in your thinking. It's not *really* the galaxy that is moving, but rather the space between the observer and the object which is expanding.. so if all space is expanding at a constant rate (which it is), objects appear to be moving away from us at a rate determined by the amount of space between us.

    You may want to check out a message I posted a bit higher up which may help you with the balloon analogy (uses bread and raisins).

    Doug
  • One way to look at it would be that the Universe is a closed bounded (yet expanding) $C-\infty$ Manifold.
    So it could be the boundary of a higher dimensional manifold. This assumes that the Euler characteristic is 2. If it is zero or -2 then more interesting "expansion" phenomena occur. I don't know a good reference for Super String theory that explores this subject. Differentiable/Riemannian geometry books tend to be a little too esoteric on this subject. A good reference book is

    "Gravitation" by Archibald, Thorne and Wheeler.

    Others are any articles by William Thurston, Peter Doyle.
    Also look at

    http://www.geom.umn.edu/docs/doyle/mpls/
    and
    http://www.geom.umn.edu
  • Actually, antimatter has been made in EXCEEDINGLY small amounts in labs. It's just an atom where the protons have been given a (-) charge and the electrons have been given a (+) charge. Deceptively simple, no?


    -Andy Martin
  • I think all of this scientific time estimation stuff is kinda funny, because all of it is based on the assumption that time is a linear constant and that it even exists at all :)

    Einstein's theories of relativity have gotten support by these same people to say that time is not a linear, but a relative value (even found support of this on the humble earth with fast airplanes).

    I'll let other posters battle about time existing...

  • Once again the old tale (Score:3)

    by Ektanoor ( 9949 ) on Wednesday May 26, 1999 @09:50AM (#1879384) Journal
    I respect the weight of NASA. It is a great institution that gave a large contribution to present human knowledge. However I cannot respect its tendency to make History out of some pieces of dust.

    The so-called "Age of the Universe" is something I would call rather childish. At least, in the way they show the public these things.

    Maybe we can determine that such metaformations such as our "Universe" could carry an age. However we must look at two major problems when we face such things.

    We don't know all factors that determined the formation of the "Universe". Recent Hubble discoveries even had risen a lot of questions on whether old ideas or hypotesis are correct at all. Not long ago there was a little squirmish about Hubble's constant itself. Not to count on such things as finiding galaxies near the "edge" of the Universe.

    Do we know the Universe? Aren't we missing anything? Up to the last century many people were convinced that the World and subsequently the Universe were not older than 6000 years. In fact this belief, based mostly on the human experience of something called "civilization", was proved wrong. Today this same civilization possesses a wider reaching eye and manages to see things supposedely 12 billion years old. However beyond that "eye" there might be a lot more. Besides it seems that this "eye" possesses some short-sightness due of a strong belief that it can't be wrong.

  • No (Score:1)

    by marcus ( 1916 )
    Not with light anyway. 'Our ' universe, by definition is only as big as the set of things that we can influence or that can influence us. I'm getting a bit out of line here, but the 'universe' might be bigger than the stuff that we can see, but it doesn't matter. By see, I mean without technological limitation. IOW, with the Hubble we can see farther than ever before, but there will be an end, some distance that we will not be able to see beyond no matter big a scope we build. That distance is effectively the end of our/the universe. The effective universe is limited to that we can see, or can see us. There is simply no way for anything beyond that radius, the distance that light has travelled since the start of the universe, to affect us. So, if there is anything 'out there' it really doesn't matter(pun semi-intended).


  • I would imagine myself inside a
    large box.

    I would start to shrink while the
    box would get larger.

    No matter how small I got or how
    much the box grew, I was still in that box.

  • Re:Age of universe (Score:2)

    by Anonymous Coward
    Leading theory now goes that there is no edge - if you were to fly in one direction, you'd eventualy gotten to the place you started from, similarly to traveling around the earth and ending up in the same place. In case of earth, we're dealing with space that seems infinite in 2 dimensions but is curved in 3d dimension while universe is continuous in 3-d but is curved in 4th D (I'm not totally sure about this point though). It all comes down to universe being finite in space but having no edges.
    - Rainy-Day

  • Faster than Light (Score:1)

    by Anonymous Coward
    Many cosmologists believe that during the first few fractions of a second the universe DID expand faster than the speed of light. However, it was spacetime itself that was expanding, not that matter was travelling faster than the speed of light. They call this superluminal expansion, and it's a rather commonly held belief. I don't remember the numbers, but it's thought that in the first few milliseconds after the 'big bang' the universe expanded to about 80% of its present size (or so).
    That's why cosmoligists talk about 'horizons' of the universe that are visible from Earth. As time goes onwards we can see more and more of the universe that was previously invisible because light from that location would have taken more time to travel to Earth than the age of the universe.
    However, it's been years since I've taken that graduate cosmology class, and I barely understood the stuff back then...
    (A tip to the ambitious - don't take a grad physics cosmology class unless you've undertaken a detailed study of general relativity. It's much less painful that way).
  • I think I prefer John Lennon's summary for readability:
    Worlds are flowing out like endless rain into a paper cup. They slither wildly as they slip away across the universe...

    Jai Guru Deva Om...



    D. Keith Higgs
    CWRU. Kelvin Smith Library
  • And I almost don't believe the rest of the universe has the same time frame as us.
  • I assure you that it's the media. Wendy Freedman presented some of this Key Project's results at Caltech a few weeks ago, and while it was an interesting colloquium, nobody was running around thinking anything was more settled than it was the day before. You can be assured that in almost all cases, the scientific community (including the authors of a result) are a lot more conservative than the media in reporting it.

    I also find it alarming that almost everywhere that I've seen the media report this result, it's phrased as "the age of the universe". They Key Project members produced a new measurement of the Hubble constant; the age of the universe requires knowing both the Hubble constant and other cosmological parameters which this project was not trying to measure, AFAIK.

  • Re:Dark Matter/Missing Mass? (Score:3)

    by astroboy ( 1125 ) <ljdursi@gmail.com> on Wednesday May 26, 1999 @04:21AM (#1879396) Homepage
    The measures of the Hubble constant include dark matter; the Hubble constant comes from the total amount of mass in the universe, so anything that interacts gravitationally is included. Dark matter is the stuff that seems to have mass but isn't `glowing' like stars, so can't be seen; it's in there. These measurements don't discriminate between different forms of mass.

    The Cosmic Micrwowave Background (CMB) definately does contribute to the mass/energy density of the universe, as you say. However, it's effect is tiny. 3K radiation corresponds to an energy density of ~(kT) ~4x10-23 J/m3, vs. on the order of 10-19 for Omega=1; so the CMB contributes about 10-4. In earlier, hotter times, the CMB contributed more; but in this cold epoch, not so much.

    FWIW: This is a NASA announcement, to sort of trumpet the end of their 10-yr `Key Project' using the Hubble Telescope. A lot of good work's been done by the Key Project Team, but the announcement isn't exactly news to working cosmologists; the number has been converging to this for a while.

  • I don't think the bible can tell me what is all in a cubic foot of soil. Ego or not, perhaps science is no more based on ego than religion is based on theological imperialism.


  • Doppler/Red shifting is always caused by a difference in speed. So the further away an object from earth, the faster it moves relative to earth.

    Red shifting can also be caused by gravity. As light travels up through a gravity well, it gets red shifted by the time dilation. From the perspective of a distant observer, time slows down inside a gravity well.

    Your other question was handled by the balloon analogy, but I'd like to add something. This type of misunderstanding arises from assuming that all the stuff in the universe was once contained in a very tiny volume and then exploded into a previously empty universe. This is not what the big bang theory states. It states that the universe itself was contained in a tiny volume. It's a subtle but important difference.

    g
  • Comment removed based on user account deletion
  • Refer back to the "balloon" analogy. The center of the ballon universe is not on the surface of the balloon, its the center of the balloon. So none of the dots on the ballon can be at the center of the universe.

    From the point of view of a dot on the balloon, the farther away another dot is on the balloon, the faster it is expanding away from you.

    Here's the math:

    *over 1 second, the ballon expands by 10%
    *there's one dot 1 cm away from you, and another 5 cm away from you
    *over that one sec., the closer dot moves .1 cm farther, the other one moves .5 cm (due to expansion)
    *The closer dot's velocity away from you is .1cm/sec, the farther dot's velocity is .5cm/s, even though the ballon expanded uniformly in all regions of its surface.

    Hope that helps. Actually, I hope that's even accurate (long time since college). Please correct me as needed.
  • Who says dolphins aren't intellignet - they spend their whole lives playing around in the ocean, never have to pay taxes, go to school or buy food. I'd say that was a pretty decent way to live.
  • Every cosmology class that discusses the formation of black holes and the creation of the universe overlooks one very glaring inconsistancy. If all matter the universe was in the same place at its start, how did it escape from this state? Even Hawking's theory of black holes evaporating where virtual particle/anti-particle pairs form near the event horizon is a slow process and nothing at all like a 'big bang'. The only way out is to say that the universe itself is a black hole (in some larger meta-universe), thus it did not escape the black-hole state. We're all still within the black-hole that is the universe.
  • Stating that H0 is 70 would enrage many scientists that happen not to be in the "high H0" camp. Recent optical data (and radio astronomical data here in Cambridge) suggest H0 to be 50 and 42 (yes, the meaning of it all!) respectively. The "high H0" camp are actually losing ground, and to understand the disparity you have to realise that many people have their careers at stake on the value of H0.


    H0 is being measured all the time, this is just one result, which is not even typical.

    D.
  • Don't forget the Big Bang Burger Bar. If you can watch the Big Bang while you eat, it must have existed before the Universe in the Great Whatzit that was there before the Universe, and is currently being pushed back by the edge of the Universe.
  • Doesn't the theory of reletivity state that certain constants (specifically the speed of light, and its associated limits) must remain the same regardless of the position of the observer and the object being observed?
    The example that I have always seen used is that if two poeple were riding motorcycles, each travelling at .9 of the speed of light (measured by an outside observer), the closing speed (measured by the rider) would NOT be 1.8 times lightspeed due to the slowing of time.

    Or is the direction (approaching vs. departing) of the two objects also a factor here?

    --Paul
  • the hubble constant is only one of the parameters you need to calculate the age of the universe. the overall mass density (commonly expressed as q_0 = mass density/critical density for collapse) and the cosmological constant (if any) are also needed. the 12 billion years is derived assuming the mass density is equal to the critical density for eventual collapse (a flat universe; q_0 = 1) and no cosmological constant. however, we don't really yet know what the values for these other parameters are, even to within a factor of two. current best estimates favor q_0 less than 1 and a nonzero cosmological constant which can result in ages of 15-20 billion years or more for the universe.

    the hubble constant is a hard thing to measure right and it's taken decades of work to get it to within 10%. measuring q_0 and the cosmological constant to a similar precision is decades more away, i think.

    tim (i'm not a cosmologist, but i play one at work)
  • Here's something fun to consider.

    Suppose you have three galaxies equally spaced in a straight line. Call them A, O and B, with O in the middle. Suppose that these galaxies are far enough apart that galaxies A and B are each receding from O at 75% of the speed of light (c).

    How fast is A receding from B?

    Did you say 150% of c? Wrong!

    Don't forget to take relativity into account. Apparently, the speed is 96% of c. Unfortunately, I forget the formula used to calculate this.
  • ...is that the time (and thus the universe) began on January 1, 1970. It will end in 2038. Don't believe the non-Unix pseudoscience.

    Unix older than time! Punchcards at 11:00!


    --
  • I'm not "dissing" Christianity at all, nor would I begrudge anybody the right to believe whatever they want. What I'm "dissing" is the extreme minority fundamentalist sects (I myself would be considered a Christian) who continually spread lies and attack "the establishment," which they view as a threat to them. The issue is not an unpopular or preposterous belief; the issue is the way that some of them feel the need to lash out at anybody who would question it. If you visited the "Earth Is Not Moving" page, you'd see plenty of references to "The Copernican Lie", attacks on science, and other such inflammatory rhetoric. This goes well beyond a deeply-held belief.

    I do respect the beliefs of Christians who believe that the universe is between six and ten thousand years old, much as I respect other viewpoints that I don't agree with (such as the whole abortion issue.) What I do not respect is the methods that their most vocal members use, and the self-righteous manner in which they condemn anybody who dares to disagree with them. When somebody comes out and claims that NASA is leading us down the road to "hellfire and eternal damnation," I reserve the right to consider that to be nutty. And I stand by my assessment. (It doesn't really matter if the above post was a troll or not; I know an individual who actually claims that the scientists at NASA are the spawn of Satan.)

    So to the fundamentalists: Believe what you want, but don't attack people for using the brains that they were given.
  • well, did you hear about the ship that made the kessel run in under 12 parsecs?

    i've always wondered what that one meant.

  • I think there's a restaurant at the edge of the universe though.

    No, there's a resteraunt at the end of the universe...


    Dodger, who saw the real-life Hotblack Desiato's Estate Agency offices the other week...

  • Most cosmological models actually say there Is an edge, but not the sense that we normally define an edge because the object itself is infinite.
    In any case, the problem with speculating what's on the 'outside' of the universe is that there isnt one. Sure, there may well be space on the outside, but it's impossible (by modern physics anyway, who knows what they'll come up with in another 20 years) to get there. The universe expands at the speed of light for a reason.. light moves at the speed of light. The actual objects (stars, galaxies, black holes, aliens etc) dont define the edge of the universe, the continually expanding light does it. So in order to be 'outside' the universe, you'd have to go faster than light obviously. Now assuming you could actually Do that, you still couldnt get out because You would be expanding the universe. As you travel outward and pass the expanding wavefront of the universe, it'd expand with you rather than you passing some barrier.
    I didnt explain that very well.. but it's an odd concept anyway. The basic point being that even were we to find a way to get to the other universes stipulated by quantum dynamics we Still wouldnt know what's "in between" them, assuming they're arranging in some way in some unimaginable superspace 'outside' our universe. (and i say unimaginable because it would be.. 90%+ of humans cant even picture objects in 4 dimensions much less the 0-infinity that'd be outside our universe.

    Dreamweaver


  • Has anybody ever wondered about anti-matter? Like how there's is supposed to be an exact opposite of you and me somewhere out there.....Or what would happen when matter and anti-matter collided causing a 100% energy conversion.


    I'm currently carrying out a long-term research project aimed at discovering who the anti-Dodger is. They've got to be female (I'm a guy), beautiful (I'm a real ugly bastard) and dumb (I'm a genius). That third requisite also means that I stand a chance of getting them into bed, so as soon as I figure out who it is, I'll be able to test that 100% energy conversion theory...


    The Big D.


    PS: Anyone know Cameron Diaz's home address?

  • Certainly estimates keep getting revised; that's what science is about. It's not a sign of bad research, but rather an indicator of a healthy field. Nobody (well, no good scientist) will claim to have definitively found *the* answer to a question; we can only approach that as sets of independent experiments converge on a consistent result. Even when this happens, better theories and better techniques can always bring the old results into question.

    Unfortunately, occasionally certain experiments get publicised too much, and out of context; the common person will see these occasional conflicting results and point to them, saying "they obviously don't know what they're talking about!". In fact, it's a much more continuous process than this. Cosmology in particular has dozens of different theories, experimental techniques, statistical techniques for *analyzing* the results of the experiments, et cetera. Dozens, perhaps hundreds of papers are published on various aspects of cosmology (of which the Hubble Constant is merely a touchstone, a good way of comparing diverse experiments) every year, you simply don't see most of them.

    -spc
  • You are of course assuming the universe is finite in size.

    If it's infinite, there isn't a center.

    Think of the balloon metaphor from earlier.

    Now imagine the balloon is infinitely big.

    It's hard to visualize.

  • what is being neglected here (Score:3)

    by sporkboy ( 22212 ) on Wednesday May 26, 1999 @03:23AM (#1879427) Homepage
    ...is that the time (and thus the universe) began on January 1, 1970. It will end in 2038. Don't believe the non-Unix pseudoscience.
  • Seems like a lot of the time the Universe is on really good acid.

  • An energy barrier... (Score:2)

    by Anonymous Coward
    ...that when you fly through it, turns certain people's eyes silver and gives them superhuman telekinetic powers.

    No, wait, - that's the edge of the /galaxy/, not the universe.

    I think there's a restaurant at the edge of the universe though.

    Ahh, need coffee. Brain not work yet.

    DG
  • What I never have understood is why the raisins aren't expanding? If space is expanding everywhere, it ought to expand the space from one edge of the raisin to the other at the same rate. In this case the raisins would all expand at the same rate and as a whole the bread would appear unchanged.

    Even if particles themselves aren't expanding, since the space between them is they must all be rushing toward each other in order to keep the atomic structure the same. So with all these particles moving to counteract the expansion, isn't there a lot of energy that no one takes into account?

    John
  • Hmmm... why doesn't a plaid old text post allow the less than symbol???
  • Actually, there are some theories that the universe isn't expanding at all. I'm not saying that they're right, but here is the basic idea: According the QED, light does not always travel at the speed of light, it is just most likely to travel at the speed of light, and averages out to travelling at the speed of light. In normal circumstances, it travels at the speed of light as well as we can measure it. However, when dealing with extreme distances, such as the distances between galaxies, these slight variations in the speed of light add up, and the light wave spreads out. This actually increases the wavelength of the light, and causes the doppler shift which has been interpreted as meaning the universe is expanding. Isn't it interesting that the universe is supposed to be expanding faster further away? Maybe this is just the result of lightwaves stretching more over greater distances?
  • I don't know if it's popular or not, but the steady-state theory says that space is constantly being created between the galaxies, explaining the expansion... Although this was largely disproved by radio dating. *shrug*
  • I think the question here is what is causing the expansion of the universe, and how it relates to the fundamental forces. Unfortunately, I don't have a good answer for you...

    Doug
  • ...does make a difference, but not as much or the way that you might imagine.

    The stick that is used to measure the universe is light, as in the speed of. When doing relativity calculations, doppler shifts, gravity effects or whatever, all speeds are referenced to the speed of light. The very words "light year" as defined as the distance that light travels in a year, is relative. Anyway, when the cosmologists talk about the age of the universe, they could just as well be talking about the size of the universe, as in "It's gotta be at least 12B years old 'cause we can see stuff that is 12B light years away!".

    Relativity effects will cause the appearance of the universe to change, but it will not change it's apparent size/therefore age. IOW, lusers in those far away galaxies will look at us and say "Wow, they are hauling ass away from us, they must be at 12Bly away, so the U must be at least 12By old!". So they see us differently from the way we see ourselves, yet we appear to be just as far away from them as they appear to be from us.


  • The objects themselves are distributed randomly, but for objects outside our own galaxy there is a catch.

    The gas and dust which make up the spiral arms of our own galaxy obscures our vision.

    We can only really see interstellar objects up and down out of our galactic plane.

    I'm not sure about the actual number of degrees which are obscured, but I believe its somewhere in the range 15-45 degrees

    Doug
  • This is exactly right. We can't see the entire Universe, we can only see our patch (the region within the so-called `Hubble radius', which is defined much the way you've done the calculation above.) Another way of thinking of this is that if, at the birth of the Universe, a protogalaxy (which is now a few Gpc away) shot a photon at us, the current age of the universe hasn't been enough time for the photon to hit us yet; so, we can't see that galaxy yet. This is an extremely important point for understanding why another question, homogeneity, puzzles cosmologists so. The bits of universe that are just barely within our horizon now but in opposite directions are not yet in each others horizon; so they haven't had any chance to interact with each other yet at all, much less come to any sort of equilibrium. However, we can see both bits -- and they look exactly the same. The CMB from both directions is identical. How on earth did THAT happen? Is it just co-incidence that all these completely so-far unconnected bits of universe were at exactly the same temperature?
  • ok, i kinda get it now. its like taking a long stick, (say, with a length of 'c') that doesn't flex at all. now, spin it in a circle. a point one inch from the center is going kinda slow cause it only goes 3.14 inches in one revolution, but a point near the end goes incredibly fast, because it has to traverse pi*'c' in one revolution. the distance between the 2 points is constant, but the speed is different. now, think of this in a linear manner.
  • We're at the center. All points are the center. Think about it this way; all expansion starts out from a point. Tha point is the center, but that point is also the universe. It seems a bit odd at first, but it makes sense.
  • Oddly enough, I remember reading something about 5 years ago that claimed the universe was 15 billion years old. They keep revising the estimates of the universe's age, sometimes higher, sometimes lower. The earlier figure of 10 billion years didn't make much sense, as some globular clusters were obviously older than that... Who knows what they'll find out next, though?
  • Just because matter drawn into a black hole reaches 'c' at the event horizon doesn't mean it would stay fixed at the event horizon. It would continue to fall towards the center at the speed of light--it just wouldn't accelerate any faster.

    Actually, the region "inside" the event horizon of a black hole is generally regarded as singular, in the sense that it doesn't satisfy axioms for spacetime upon which general relativity is based. Really, no one knows what happens beyond this boundary; we can only decide behavior at the boundary itself.

    -josh
  • All motion is relative, so sayeth Albert Einstein. As such, what we measure is the rate at which objects are moving away from us, as observed by us.

    If a galaxy is seen to be moving away from us at 1000 km/s, an observer halfway between that galaxy and ours would see both of them receding at ~500 km/s (approximately, the effects of special relativity are quite small at such paltry speeds).

    To use your analogy, suppose you were sitting at the exact point someone hit the water with the stone. Both ants would be moving away from you at the speed of the wave (assuming they are on miniature surfboards). Each ant, in his own "stationary" reference frame, would see you moving
    away at the speed of the wave, and would see the other ant moving away at twice the wave speed.

    This is, of course, a classical example. If the speeds are relativistic, the expression is no longer v_r = v_1 + v_2, rather v_r = (v_1 + v_2) / (1 + v_1*v_2/c^2), limiting the relative velocity to the speed of light, c.

    Eric
  • For a long time I have had this question in my head. The one oppurtunity I had to get this question answered by some reputable scientician (Simpsons Reference :-), viz. Stephen Hawking, I chickened out.

    Anyway, my question is this:

    We say that the universe is expanding because of the doppler red shift in the light that reaches us from the stars in the outer reaches of the universe. We are basically looking into the past when we are observing the stars in the outer reaches of the universe.

    . What if the expansion of the universe is just something that used to happen in the past? Could it be that the expansion of the past has stopped? Maybe the universe is just in steady-state now.

    Would welcome the views of all you folks.

  • No, scientific studies have shown conclusively that noone has ever wondered about that.
  • No, it is not a coincidence that the age of the universe is 1/H (H=Hubble
    Constant). The Hubble Law can be written as:

    v = Hd where v=velocity of galaxy, and d=distance of galaxy. this is
    also where the funky units for the Hubble Constant come from.
    Astronomers like to measure distances in Mpc, so simply multiplying H
    by the distance in Mpc gives the velocity in km/s. In actuality it is
    much easier to measure the velocity, so astronomers usually divide H by
    the velocity to get an idea of the distance.


    Here is a quick estimate for the age of the universe: Consider a huge
    explosion of galaxies at time t=0. After a while when we look out at the
    galaxies, the faster ones will have moved further. A specific galaxy
    will have moved:

    d = v t where d is the distance, v is the velocity, and t is the time
    since the explosion.

    This can be rewritten as v = d / t. Now compare this equation to the
    Hubble law -- H must equal 1/t, or t (time since explosion) must equal
    1/H.

    This is the Astro 101 explaination. The correct derivation requires
    differential equations and a many assumptions about the flatness and
    density of the universe. The correct values for the age of the universe
    are:


    0 t
    t = 2/3H^-1 for a just dense enough universe

    2/3H^-1

    What always got my goat is that H is called the Hubble constant, but it
    changes with time.

    -=[doug]=- who has never even pretended to be a cosmologist
  • Think of it in terms of dots painted on a balloon. When you blow up the balloon (that is, as the Universe expands), each dot recedes from the other, and the farther apart the observer is from a dot the more rapidly it recedes.

  • The universe is a black hole. Seriously! (Score:2)

    by Anonymous Coward
    Take the known mass of the universe (iffy, but still) and calculate the schwartzchild radius for a black hole of that mass. It turns out to be just about the known size of the universe. Now think about matter falling into a black hole. The matter accelerates until it reaches a speed of c which it cannot exceed. This speed is reached at the black hole's event horizon, not at it's 'center'. So black holes are actually a spherical shell of super-dense matter all packed in at the event horizon. And since we all know (I hope) that there is no gravity inside of a uniform hollow shell of matter, the inside of a black hole would be a complete closed off section of space, populated by whatever matter was present inside when the black hole formed, which is now free to safely float about and coalesce to form things like galaxies, stars, planets, you, me, etc. all blissfully unaware and independent of the harsh black hole environment just 'outside' the universe. The outer meta-universe where our black-hole universe exists may itself be a black hole in a meta-meta universe. Can we leave this universe? Maybe but it's doubtful. Our universe is finite in volume but unbounded. You can travel in any direction forever, like a ship sailing in any direction on a world with only ocean and no land. It can sail in any direction endlessly and never reach an 'edge of the world' yet there is still a limited sized ocean over which to sail. The universe is identical to this except that it is finite over 3 dimensions. For you CS types, imagine it as a 3-D array doubly linked in each of the 3 dimensions with the array elements at the 'edges' of the 3-D array cube linked to the element at the opposite end of the cube. Now start anywhere in the cube and follow links in any direction you like, change your direction of travel at any time. You can traverse array elements forever in any of the three dimensions and yet never reach a boundary to a 3-D universe. Our universe, like this, is closed and finite, yet unbounded. This concept is difficult for many to grasp, but I hope these examples help. Back to 'can we escape the universe?' Maybe. If a gravitational disturbance in the meta-universe (say another black hole [universe]) passes close to ours, it can warp spacetime enough to create a link from our universe to another (either the passing black hole or to the meta-universe or both). This link could be temporary or it can expand until our universe actually merges with another. These links are what are called 'wormholes'. Everything I've said here is, of course, all highly speculative may be utter bunk or absolute truth. You decide. Don't flame me. Better yet, bug your physics professors'. They tend to avoid thinking about sensational stuff like this because it has the potential to get them branded as heritics and philosophers by their peers. And this concept of 'proper or right thinking' as definer by their peers, often limits inspiration. Off the wall, or even wrong postulates by people like you and me may make them think of something they would not have ever imagined before. But get 'em thinking. Who knows. Maybe someone, somewhere will make some real discoveries. Most of all, have fun! Science is fun because reality is fun!
  • Actually, if you'd read the article, you'd see that they talk about the previous estimates being either 10 billion or 20 billion years old, depending on which "camp" you subscribed to... With this new evidence, they are all coming closer together (they said their calculations have a 10% error rate... much better than power of 2).

    Of course, you should take EVERYTHING with a grain of salt... the fact that so many people don't is what is wrong with this world.

    -WW
  • I've wondered this many times. One theory I came up with is this: Inside a Universe there are many galaxies, inside galaxies there can be many solar systems, so maybe there is something larger than a universe that contains many univereses. It's hard to believe that there would be absolutely nothing outside of our universe and that things leaving our universe would just disapear. To me that's equivalent to thinking the earth is flat and that people can fall off the edge.

    Or maybe the universe curves back onto itself like the surface of a planet, making the universe one large object that keeps growing in size, but has no edge... It would be like a balloon getting blown up. Every point on the balloon keeps getting further away as the balloon gets blown, but there is no edge to the surface of the balloon.

    Just a thought...
  • yeah, the theory of general relativity :)

    when they say "expanding universe", they mean that indeed space itself is expanding. the matter in the universe is just being carried along for the ride. expanding/contracting space is one of the profound predictions of einstein's theory of general relativity, though he didn't believe it at first and added a constant to cancel it out. a few years later when edwin hubble discovered observationally that the universe was expanding, einstein regretted adding the constant and dubbed it his "greatest mistake".

    however, there is now evidence that some form of that constant is needed so al might have been right in the first place.

    tim
  • Doppler/Red shifting is always caused by a difference in speed. So the further away an object from earth, the faster it moves relative to earth.

    But this leads to another interesting question: If everything moves away from the original center of the universe, we should measure different amounts of red shifting for equidistant objects, depending on whether they line up with earth and the center of the universe, or whether they are orthogonal to earth. In any event, the distance to earth should get bigger over time, but in the first case faster.

    As far as I know, that's not the case, which would mean that earth must be very close to the former center of the universe. Does anyone know more about this?

  • Aha! But you've forgotten to put a link to this site [biblicalastronomer.org], which conclusively refutes the Satanic view that the Earth is not the center of the Universe! After you've read through that, buy the book! [fixedearth.com]

    I'm fairly certain that the above post is a troll, but I've included these two links to show the truly preposterous nature of creation "science" (that is, start out with a conclusion that must be reached at all costs, and then start looking for observations that could be interpreted as supporting that conclusion, while discarding everything else that does not.)
  • "No; after disappearing down the back of the sofa/into the depths of the washing machine/through the lining of your coat pocket, those things actually appear as antisocks and antipens in a parallel universe. Down the back of some sofa in some universe there must be a fortune in anticoins."


    Close, but no cigar. Most of these items are short-lived exotic things. i.e.Socks with negative energy mass. This means that they are destroyed fairly quickly after they are lost (on the order of a few milliseconds). Man, if only we could collect exotic matter socks... warp drive [islandone.org] would be possible...

    //end humor

  • Combining Hubble's constant measurement with
    estimates for the density of the universe, the team determined that the universe is approximately 12 billion years old -- similar to the oldest stars. This discovery clears up a nagging paradox that arose from previous age estimates. The researchers emphasize that the age estimate holds true if the universe is below the so-called 'critical density' where it is delicately balanced between expanding forever or collapsing. Alternatively, the universe is pervaded by a mysterious 'dark force' pushing the galaxies farther apart, in which case the Hubble measurements point to an even older universe.
    The emphasis is mine. Is it the media or the scientists that make these proclamations seem so cut and dried, like, "whew! now that's settled!" when in fact, there is so much guesswork, any conclusion is just not certain? I think it's the scientists, but they should know better.
  • Oops. I hoped that those things would turn out as superscripts. 10-23 is 10^(-23), 10-19 is 10^(-19), and 10-4 is 10^(-4). sorry.
  • Found virus... Windows detected.
    Remove (Y/N) ? Y
    Removed Windows
    Rebooting Universe
  • observations of certain species of stars called "Cepheid" variables were used to obtain these results. these kinds of stars have a well-defined relation between their period and luminosity. so if you can measure how fast they vary, you can derive fairly accurately how intrinsically bright they are. once you know how intrinsically bright they are, you can use that together with how bright you observe them to be to get their distances. do this for a bunch of these stars in a galaxy and you can get a fairly accurate distance to that galaxy. this team did just that for a bunch of galaxies out to much greater distances than was possible from the ground before HST and thus derived the Hubble constant.

    so, the Hubble constant was the end and Cepheids were the means.

    tim

  • I, maybe (Score:1)

    by gas ( 2801 )
    Could be hard, I'd say there's a big risk the universe takes us with it (if it at all ends, that is). But now when you mention it I'm going to change my plan a little.

    It was to live until
    1. I get bored, or
    2. The universe ends and destroys me too.
    (Not taking accidents into account)

    Now I think that maybe instead of destroying all copies of me when I get bored I will set the alarm clock to the end of the universe (who knows, I could get a good last meal too :) just to see what it's like.


    --
    How? When I start to grow old and likely to die (or earlier if someone proves it works) I will conserve myself (some kind of freezing sounds doable) in a way that preserves the brain structure and memories. When finally someone can build artificial, electronic brains (or emulators) I will start to live again. And do backups every 'clockcycle' of the emulator to as many safe places at possible. Except (almost) immortality it also gives benefits such as: any kind of body, remote controlling, eating and breathing only when I like to, lightspeed traveling, live quake :), being able to switch off for a while when things get dull, harmless drugs and sleep speedup.
  • Ok, feel free to check my math. I calculated that if the universe were 14839 _million_ light years across, anything at that distance would be moving away from the other side at the speed of light. Of course, we don't have anything strong enough to see this, but could the universe be bigger than we think because things are moving away from us too fast and we can't see them?

    According to the story things are moving away at 160,000 MPH for every 3.3 million light years. 160,000 miles is roughly 240 million meters.

    240,000,000/3600s = 66,666m/s for every 3.3 million light years. 299,792,458m/s (speed of light in a vaccuum)/66,666m/s = ~14839 million light years across and the two objects are moving away from each other at the speed of light.

    All values are approximate except the speed of light (speed of light found at http://physics. nist.gov/cuu/Constants/index.html?/table2.html [http]).
  • Comment removed based on user account deletion
  • To comment on the previous post... this isn't technically correct.

    Capital omega (you try typing one) is the ratio of the overall (mass + energy + cosmological) density divided by the critical density (remember, mass IS energy, E=mc^2). In a flat universe, Omega = 1; closed, Omega > 1; open, Omega 1.

    Open means the universe will expand forever, with no limit on the physical size. Flat means the expansion will slow to zero in an infinite amount of time, producing a finite physical size to the universe. Closed means self-gravitation of the universe will win out, halting the expansion of the universe, and causing it to re-collapse, presumbly into a "Big Crunch".


    The baryonic matter (massive particles such as protons, neutrons, etc.) and photons (light/energy) are all the stuff we see, and is though to have density of about 0.1-0.3 of the critical density.

    The cosmological constant (the was invented, then abandoned by Einstein) is a mathematical embodiment that the "vacuum" of space is not actually empty, but full of energy fluctuations that create particle/anti-particle pairs, which annihilate each other in an incredibly short amount of time. This "zero-point" energy would add to the total mass/energy of the universe, and increase the density.

    q_0 is the deceleration parameter, equal to 1/2 for a flat universe. If q_0 > 1/2, the deceleration rate is greater, and the universe is closed. If q_0
    The current theory is the the density of baryonic matter and light/energy (Omega_b) and the contribution of the cosmological constant (Omega_Lambda) add up to exactly equal the critical density, Omega_total = 1.

    Eric (who just finished a stint as teaching assistant for a class in astrophysics and cosmology).
  • Combining Hubble's constant measurement with estimates for the density of the universe, the team determined that the universe is approximately 12 billion years old.

    Obtaining a value for the density of the universe doesn't seem to be a very easy operation, yet they've glossed over it as an obvious point. How would you obtain such a number? It is clear, however, that the value is finite and non-zero. Finite because vacuums exist, non-zero because we exist.

    Here's my issue: we have seen consistently that every natural shape is fractal. Consider the cosatilne, the leaves on a tree, broccoli, the shape of a starfish, I could go on forever. Wouldn't it then make sense that the universe is also a fractal?

    One way to define a fractal is infinite in the nth dimension while finite in the (n+1)th dimension. Something like an infinitely long line contained in a finite area.

    If the universe has a beginning and an end, then it is finite in time. To be fractal it should, therefore be infinite in space. An infinite voulme, given a non-zero density (which is proven very simply by our existence) implies an infinte mass of the universe. That means we can never find the end of the universe because there is no end to the universe!!

Slashdot Top Deals

Whatever is not nailed down is mine. Whatever I can pry up is not nailed down. -- Collis P. Huntingdon, railroad tycoon

Close