AAS Post #6: The cosmological not-so-constant

By Phil Plait | January 11, 2006 10:41 am

What’s powering the Universal acceleration?

This may be the biggest question is modern cosmology, the study of the structure and evolution the Universe. We’ve known for nearly a century that the Universe is expanding. Distant galaxies appear to be moving away from us, indicating the Universe gets bigger every day. This was a hugely shocking result in the early 20th Century, but bigger shocks were in the works.

In the 1990s, two independent teams of astronomers determined that not only is the Universe expanding, but that expansion is accelerating, growing. Not only is the Universe bigger every day, it’s getting bigger faster. This was completely unexpected; everyone assumed that the gravity of all the combined matter in the Universe acted as a cosmic brake, slowing the expansion. Some people even theorized the gravity would grind the expansion to a halt, and the Universe would recollapse on itself in the dim distant future.

But that was wrong. Something, some mysterious something, was pumping energy into the Universe, acting — to stretch the earlier analogy a bit– like a cosmic gas pedal. This is so bizarre it’s hard to wrap your head around it. But the data all point that way.

But there’s still a problem. To be able to measure this acceleration, you need to look at really distant objects. The effects nearby are way too small to measure, so you need to look at objects as far away as possible. To astronomers, this meant supernovae, exploding stars– they’re bright enough to see even from billions of light years away. It was tough– you need to be able to examine a lot of supernovae, and each one is a bit different. This difference can screw up your results! So astronomers had to figure out a way to correct for all these little individualities. In fact, it is possible to do this pretty well, and it was the results from these studies which uncovered the acceleration of the expansion.

After studying this for some time, astronomers think that the acceleration is caused by some form of previously unknown energy permeating the cosmos. It acts like a pressure, forcing the Universe to expand ever-faster. One key thing is that astronomers assumed that the force by this "dark energy" is constant in time. In other words, it’s always been the same, and always will be. Einstein was the first person to propose this, and he called it the Cosmological Constant. But to test its constancy, you need to see really distant objects, even farther away than we can spot supernovae. Seeing something 10 billion light years away is good, but 12 would be a whole lot better. The effects of expansion are a lot more obvious that far away. But what can be bright to be seen at that numbing distance?

There may be something. Gamma-ray bursts (called GRBs for short) are titanic explosions that dwarf even supernovae. Theoretically, they can be seen at distances of up to 13 billion light years! So astronomers turned to them to use as milestones in the distant Universe.

The problem is, GRBs are stubbornly individualistic. Every one appears to be really different from the other. A half-joking expression among astronomers is, "When you’ve seen one gamma-ray burst, you’ve seen one gamma-ray burst". It seemed impossible to be able to use them to measure the acceleration.

But now an astronomer thinks he’s found the key. Brad Schaefer, from Louisiana State University, has been studying the problem. He thinks that he’s found five separate characteristics of GRBs that, when viewed as a whole, herds this unruly lot into a usable yardstick. His numbers are still not absolutely rock solid, but what he’s found is very intriguing: the GRB data seems to show that the amount of dark energy in the Universe is not constant with time. It appears to be greater now than it was in the distant past.

In the plot above, Brad shows the distance for a GRB plotted against its redshift, basically how fast the expansion of the Universe is carrying that burst away from us. What you need to see in that graph is that the GRBs all appear to fall below the prediction of their distance predicted by having a cosmological constant. The error bars on the most distant (high redshift) objects are big, but there is enough data there to cast doubt on the cosmological constant being quite so solidly constant.

Let me be clear: if this is true, it is a fundamental change in the way we view the Universe. It’s weird enough that the Universe is accelerating, but if that acceleration is itself accelerating, that makes things a whole lot weirder. It’s a huge monkey wrench in the works of cosmology, and if it’s true it’ll have theorists scrambling to figure out what’s behind it. Mind you, this doesn’t cast doubt on the Big Bang theory itself, it just changes one aspect of it.

But is it true? Right now it’s hard to say. Brad has studied 52 GRBs, which is a nice sample, but needs more. At current rates of detection, we’ll probably double this number in a year or two.Statistically, the confidence in this new model is at the 97% level, which that there is a 3% chance that this is just due to randomness in the data (like seeing three heads in a row when you flip a coin 5 times– that may be because the coin is weighted, or it may just be a coincidence). 97% sounds pretty good, but we’re talking about a major change in physics, so we’d rather have that at the 99.99% level!

At the press conference held this morning on this topic, Brad did an excellent job showing that this is a preliminary result, that’s it’s not as confident as it needs to be to overturn current thinking in cosmology, and that as time goes on we’ll get more data we can plug into it. I was proud to be a scientist, to hear another scientist carefully explaining how results are tentative. As cosmologist Michael Turner said after the press conference, "It’s an exciting time to be an astronomer. The mysteries run — literally — from our own back yard to the edge of the Universe."

CATEGORIZED UNDER: Astronomy, Cool stuff, Science

Comments (58)

  1. No One Of Consequence

    Preface – All I know about cosmology/astronomy I’ve learned on the web and Science magazines.

    Ill-informed Question: Since you can create a solar sail that provides acceleration using the solar wind, is it possible that galaxies could be pushing against each other with galactic levels of solar wind, accounting for some of this acceleration?

    My gut feel is that it wouldn’t be near enough force and the galaxies themselves don’t have the right properties to be pushed, but who can comprehend what galactic levels of solar wind would be like.

  2. It’s not the stuff embedded in space which is being pushed, it’s that spacetime itself is being stretched. Two objects at rest with respect to one another will find themselves further apart after a time because the intervening space has stretched.

  3. ToSeek

    I knew Brad from when he was working at Goddard (and attending meetings of the local Sherlock Holmes society). He’s a very outgoing guy – I fully expected to see him making headlines eventually, so I wasn’t too surprised to see his name show up.

  4. M Campbell

    > Two objects at rest with respect to one another will find themselves further apart after a time because the intervening space has stretched.

    Wouldn’t the space which the objects occupy also stretch, making them “bigger”, and then NOT any “further” apart (relative to their own size)? If all of space-time is expanding, what reference frame do we have from which to “measure” it? Just red-shift #’s? (Or is that enough?)

    I’ll admit that like the OP, I don’t know nor understand much about this stuff.

  5. Maurizio

    Would you believe it…the scientific term for the first derivative of acceleration is…”jerk”


    Who will be the first one to post a joke about the increasing jerkiness of the Universe?

  6. Bob Hawkins

    > Would you believe it…the scientific term for the first derivative of acceleration is…”jerk”

    Anyone who rides the trolleys in Boston would believe it.

    In a way, the cosmological constant is a form of “continuous creation.” It’s energy that continuously increases, rather than hydrogen atoms, but e=mc^2. The Great Wheel takes another turn.

  7. Marlayna

    From what I gather, the jerk doesn’t seem to be increasing. If the jerk was increasing as well, I think that would be noticeable.

    I find this discovery really cool! This whole dark energy business is getting more and more intriguing!

    @M Campbell: Objects remain as they are due to electromagnetic and nuclear forces, so only the distances change.

  8. SimpleGuy

    Everytime I hear about the universe expanding and think about the big bang, the vision of a balloon comes to mind. This begs the question as to where the initial force (the “air”) to expand the balloon came from and if we are “stretching”, what are we stretching within? And, of course, I always wondered where black holes went.

    But, along these simple lines, because I am a simple guy, could the discrepancies in the acceleration (or “jerkiness”) be caused by black holes? My initial thought was that it was gravity related, but that would seem to a constant. Perhaps the rapid infusion of more dark matter?

    Always in awe, a simple guy.

  9. Dave Kary

    Looking at that data, I’ve got to say I’m glad Brad has emphasized how tentative it is. When the error bars are that big and the phenomenon is as poorly understood and GRB’s, you’ve really got to worry about systematic errors that we just don’t know about yet. It wouldn’t take much of one to completely eliminate the discrepancy between the data and the “Constant” prediction.

    I know Brad Schaeffer will do a careful job on this one, but I’d really like to see more of the model behind it as well as much smaller error bars before we can be too confident of the result. As my thesis adviser liked to tell me, “Never trust an observation until it’s been confirmed by theory”.

    Dave K

  10. In this whole line of argument (dark matter – dark energy – etc.), I just get the feeling everyone is missing something big. That someone (much smarter than I) is going to find the key and everything will fall into place. Something of the order of placing the sun at the center of the universe explains the movement of the wanderers, IE planets. If this discovery pans out, it makes me think the “Aha!” moment is just around the corner…

  11. OK, it might be [b]the[/b] stupidest idea ever, but maybe there are several other universes, which mass attracts the mass in our universe (and vice versa, I presume) and therefore the expansion is accelerating, and not just accelerating, but accelerating quadratically?

    *hides in the bushes*

  12. Nice language Sophie.

    Anyway…. Ever notice a balloon before it pops while you’re blowing it up? It starts to expand faster.

    Just sayin’ …


  13. Wow, sounds promising. I love a good mystery as much as anyone, but it’d be fantastic if Schaefer’s model holds up. Exciting!

  14. J Dawson

    You missed an apostrophe there.
    Be nice.

  15. Dan Gerhards

    “Wouldn’t objects get bigger?”

    To answer M Campbell’s question, no. As far as I understand it, the space within objects does expand. However, the other forces involved are so much stronger than the expansion (on small scales) that they hold the atoms together against that tiny push. It’s only in vast tracts of nothingness that we can see anything happen. That’s why objects seem to get father away from each other rather than bigger.

    That still leaves the question of why the quarks and electrons themselves don’t get bigger, but you have to remember that they aren’t objects in any classical, physical way. Probably they can’t grow because they don’t have any volume.

  16. Just an undergrad, but…

    Since gravity works no matter what the distance, and drops off relative to distance, then shouldn’t we see a graph like that even with a constant dark energy acceleration? As gravity’s influence puts less and less of a braking force on the expansion? Similar to TotalAccelleration=CConstantAccel-(1/Distance^2), though (1/Distance^2) isn’t right since as everything gets further apart, the gravitational pull of everything else drops off faster than that. I’d like to see the graph of the correct form of that equation overlayed on the one in the post, even if it’s not scientifically useful.

  17. In response to the “Wouldn’t objects get bigger”, that’s something I’ve always wondered as well. I believe the answer is just what Dan Gerhard said. But then my questions are:

    a. Wouldn’t this expansion affect light as well, making light from older (further) objects redder than what red shift itself explains (like the cosmic microwave background, isn’t that why it’s “temperature” is so cold)? If so, do our methods for calculating speed based on redshift take this into account?

    b. If everything is expanding, why aren’t the effects of the quantum “foam” seen on larger and larger (greater than planck-length) scales? I’ll bet it has something to do with the uncertainty principle. 😉

    c. Less seriously and more whimsically, how do we know that the universe is getting bigger and that instead we (matter, forces, etc.) are not all getting smaller?

  18. brent wiese

    bravo. i’m not a scientist or student of science. but i visit your site nearly every day because i like the information, you present it all so that even us regular people can understand, and your enthusiasm is contagious.

    my four year old came home from pre-school today. she was all excited to tell me about the sun, and how mercury is the closest planet to it. same sort of excitement. i’m thrilled. we both have so much to learn.

    thanks for all your effort. thanks for sharing.

  19. Dan Gerhards

    More questions:

    a. That’s what red shift IS. Reddening by expansion isn’t a seperate effect that has to be taken into account, it’s the only effect. (You’re right about the microwave background: It’s been red shifted for billions of years.)

    b. Expansion has to be measured against something. If constants like the Plank length were getting larger too, we wouldn’t notice any expansion at all. But the consants AREN’T expanding while the universe is. Also, no pair of particles is around long enough for the expansion to separate them. (Actually, we can see the affects of quantum vacuum fluctuations on macroscopic scales. Look up the Casimir effect.)

    c. What’s the difference? Everything’s relative!

  20. Good point, Bryan. Add less resistance from gravity to my (tongue-in-cheek) weaker space-time fabric and one would have to expect the expansion to speed up!


  21. PK

    SimpleGuy Says: Everytime I hear about the universe expanding and think about the big bang, the vision of a balloon comes to mind. This begs the question as to where the initial force (the “air”) to expand the balloon came from and if we are “stretching”, what are we stretching within?

    According to GR (General Relativity) space is not stretching within anything! It might be “convenient” to think about curved/stretched space as a hypersurface in a higher dimension (just like the surface of a balloon is a curved two-dimensional surface embedded in a flat 3D space). But the beautiful mathematics of GR circumvents the need to introduce these higher-dimensional flat spaces.

    If there was ever to be held an election for the greatest achievement of Man (you know pyramids, great wall of China, moon landing, etc.) I would vote for GR!

  22. Theroy has expanded fast. Remember Fred Hoyle and his “steady state universe”?

    Some of the language being used in these blog comments are part of the “smack down” theroy.

    Oh well, as we wrestle with this cosmic engine, there shall be road rage…. :*)

  23. Irishman

    ruidh Said:
    >It’s not the stuff embedded in space which is being pushed, it’s that spacetime itself is being stretched. Two objects at rest with respect to one another will find themselves further apart after a time because the intervening space has stretched.

    Define “at rest with respect to one another” while the distance between them is growing. Isn’t that velocity by any other name?

  24. TJ

    Maybe as galaxies are consumed by black holes over the next few billion years, the gravitational pull will strengthen enough to overcome this expansion.

    Was there a previously collapsed universe that existed before this one, which contracted on itself until it reached a critcial mass, then caused the Big Bang?

    Is this the first universe or the 578th? or the millionth?

  25. a. Doesn’t the red shift also have a doppler component? Maybe I’m asking the wrong question, but is the redshift caused by the expansion of space (and therefore the lengthening of the light’s wavelengths along with it) or by the accelleration away from each other of the objects within space (and therefore, the further back in time and further away you look, the greater the difference in velocity between the emitter and the reciever, and therefore the greater the lengthening of the observed wavelength by doppler effect), or is it some combination of the two? Or, are they equivalent?

    I really should take a few more physics classes. :-)

  26. TJ, a black hole has the same gravitational pull as the mass it sucks in (maybe a bit less due to all of the radiation the stuff gives off as it falls in), so the net gravity would remain the same. For instance, if the sun were instantly replaced by a black hole of the same mass, it’d get really dark outside (8 minutes later) but that is all that would change. The earth wouldn’t change it’s orbit or anything, and all of the planets and asteroids and everything else would continue on the same path. Unless you count the radiation/solar wind pressure from the sun, but that contribution is really small.

  27. TJ

    So it doesn’t draw things in? There goes my illusion.

  28. SimpleGuy

    PK said: “According to GR (General Relativity) space is not stretching within anything! It might be “convenient” to think about curved/stretched space as a hypersurface in a higher dimension (just like the surface of a balloon is a curved two-dimensional surface embedded in a flat 3D space)…”

    So, simply, the big-bang just happened, we were created out of nothingness, we are expanding, it’s happening quickly (logarithmically?), and maybe someday it all might just collapse back within itself (to nothingness?). :-)

    I’m not saying that there *has* to be another dimension that we are existing within, but it would seem to be simpler. That way I can envision the balloon methaphor with the black holes as pinpoint leaks (which is what I was trying to explain as the cause of the “jerkiness” in the expansion). Another simple thought was that the big-bang was the the other side of a black-hole singularity. And, that would need the extra dimension concept. :-)

    Does mathematics deny this possibility?

    But, as I am a simple guy and not a scientist, this is all just interesting to me, and I am sure hundreds have already put more thought into it than I. :-) In constant awe.

  29. Interesting post and comments.

  30. PK

    SimpleGuy Says: So, simply, the big-bang just happened, we were created out of nothingness, we are expanding, it’s happening quickly (logarithmically?), and maybe someday it all might just collapse back within itself (to nothingness?). :-)

    That’s right, except that it seems we’re not collapsing back.

    Some string theories (in which I am not an expert) say that the Big Bang is a collision between two “branes”. I guess you would need extra dimensions for that. In any case, we won’t know how to deal with the moment of the Big Bang properly until we have a working theory of quantum gravity.

    Bryan Turkelson Says: Doesn’t the red shift also have a doppler component?

    The red shift due to the expanding universe is not a Doppler shift. If a small quasar (billions of lightyears away and thus redshifted) was suddenly sent towards us due to a gravitational slingshot of bigger quasars, its spectrum would be less redshifted. This is a Doppler effect, and independent of the expansion of space.

    Another way of thinking about it is that the cosmological redshift (due to expansion) causes a photon to lose energy during travelling to the gravitational potential (which is there because psace is curved).

  31. OK, so exactly as my point was originally, to any measure of redshift there are several things doing the shifting:
    a. the expansion of the universe (which apparently has the biggest effect)
    b. doppler shift (due to the speed the measured object is moving toward/away from us)
    c. gravitational redshift (photons lose energy escaping gravity, which is negligible for everything except black holes I think)

    Here is the logic behind my question: The universe is expanding. Everything is moving away from each other. So, the furthest things away are moving away from us the fastest. Therefore they should be redshifted by the doppler effect AS WELL AS the expansion of the universe. Furthermore, if the expansion is accellerating, the effect due to both redshifts should be increasing. My question was basically, how much does each type of redshift factor into the calculations?

    If everything is moving away from each other then we have to be going pretty fast compared to things on the other side of the universe, especially if we’re accellerating. Relativity says you can consider us to be at rest, and the rest of the universe in motion. So the doppler effect I’m talking about is like a police car accellerating away from you- You’d see the taillights get redder and redder just like the siren gets lower and lower.

  32. Ah ha!

    As usual, the answer is found on wikipedia.

    “While this redshift of distant galaxies closely resembles what would be seen if distant galaxies simply had recessional velocities, in general relativity stretching of spacetime is different from the physical movement of the source. These galaxies are not believed to be receding; instead, the intervening space is believed to be stretching, which is subtly different. Nevertheless, astronomers (especially professional ones) sometimes refer to “recession velocity” in the context of the redshifting of distant galaxies from the expansion of the Universe, even though it is only an apparent recession. More mathematically, the viewpoint that “distant galaxies are receding” and the viewpoint that “the space between galaxies is expanding” are related by changing coordinate systems. Expressing this precisely requires working with the mathematics of the Robertson-Walker metric.”

    That makes sense to me. It was due to a breakdown of language thought that distant galaxies were actually moving away from us, in addition to space itself expanding. However… I’m wondering what the “subtle difference” between these two models is.

  33. sgmkevin

    Lemme move my soapbox up here a little closer to the mic, ok, little bit to the left, good. Now, my thoery is that the nature of existence is to expand. To occupy more space if you will. My question is that are we sure that something out there isn’t “pulling the universe apart? Is there something outside of our universe that is pulling space causing it to expand. Maybe when you look at it this way it might make more sense.

  34. steveo

    Wasn’t Albert brilliant? Look how close he was way back when! We all assume that everything has a nice neat beginning and end. Maybe the truth doesn’t fit so well. When truth is found I’ll wonder “Why didn’t I think of that?”.

  35. As someone pointed out, this is a great opportunity to publicize “jerk”. :) As I recall, in some biological contexts it is the relevant property, though I do not remember any details. Now we get to see its relevance at the very large. Interesting.

    As a friendly aside, I wish physicists and astronomers would stop equivocating on the meaning of “universe”, because we need a good word to refer to “everything that exists”. Using that word to mean “local hubble volume” or something is misleading, to say the least. (This would stop religious misinterpretations of the big bang, too.)

  36. rakidd

    Maybe we are not in the time period of expansion and collapse of the Universe that astronomers previously thought we were. Current thinking says the Universe is expanding and should start slowing before stopping and collapsing. Maybe it is way past slowing and stopping and is already collapsing. That would mean that galaxies would be accelerating away from each other (those galaxies closest to the center of “everything” are being pulled in faster than galaxies farther away from the center), which complies with current theory, and that the acceleration is accelerating as all galaxies head toward the center, which explains the result presented by Brad Schaefer.

  37. Irishman

    sgmkevin Said:
    >My question is that are we sure that something out there isn’t “pulling the universe apart? Is there something outside of our universe that is pulling space causing it to expand. Maybe when you look at it this way it might make more sense.

    That idea relies on the proposition that there is an outside of the universe. Since we currently (and may never) have no way to see outside our universe, that proposition is speculation at best, and perhaps even unfounded wishful thinking. Whatever it is, it is difficult to investigate scientifically.

    Keith Douglas Said:
    >As a friendly aside, I wish physicists and astronomers would stop equivocating on the meaning of “universe”, because we need a good word to refer to “everything that exists”. Using that word to mean “local hubble volume” or something is misleading, to say the least. (This would stop religious misinterpretations of the big bang, too.)

    This is a historical problem for names for “everything that exists”. The World was one of those collective words, but to most people now refers to this one world we live on, Earth. The Solar System may or may not have been used that way at one time, but the conception certainly was that way – the word “heliocentric” is based on the concept that everything is centered on the Sun. The Galaxy was also one term – back before we knew that those fuzzy spots on images were other “island universes”, or galaxies. Universe was just the next big word to describe all those different galaxies and everything in between.

    The problem arises in that we have defined “universe” strongly by the existence of “universal laws”, i.e. those descriptions and constants that define how the universe works. So it is only natural for cosmologists to talk about “other universes” when they are talking about pockets of existence that may operate with a different set of rules/constants. How can they be our universe when they don’t conform to our universal laws? Nevermind the origin of the word “universe”. We’re stuck with a concept of universe that limits it’s scope.

    A couple other words still exist. One is “multiverse”, which is mostly a favorite of Science Fiction writers. Another is “Cosmos”. Yes, you can still use “Cosmos” to mean “all the universes and any interrelations between them”, or “everything that exists”.

    Of course there is the problem that we aren’t really sure if there is anything beyond this universe.

  38. Nothing goes faster than the speed of light, not even gravity. Just as with light, if there is anything “outside” our viewing radius, it must have been there a really long time ago (longer than the closer-in stuff). Also, it’s got to be dark, because if it were bright but has been there long enough time for the gravitational effects to reach us then photons have had time to reach us too.

  39. Bryan mentions:

    Nothing goes faster than the speed of light, not even gravity.

    That brings up an interesting, to me, thought concerning gravity. We always talk about nothing can escape a black hole, not even light. But that isn’t entirely correct. Gravity does.

    So while the effect of gravity propogates at the speed of light, gravity still must be fundamentally different from light (ie, dissimilar from ElectroMagnetic Waves/Particles). Neither Matter nor Energy, Gravity is some other fundamental thing. So what is it?


  40. PK

    The gravity of a black hole manifests itself in a curvature of space and time. When you say that gravity propagates at the speed of light, you mean gravitational waves. Wiggling a mass at one location will have an effect on another mass far away only after the generated gravitational waves managed to get there. A gravitational wave generated inside the horizon of a black hole will not escape the BH, because it is a physical signal.

    Another way of thinking about it is that a stationary/static curvature cannot be used to send information from one location to another. It is, if you like, the silent telephone line. The GW are then the telephone signal.

  41. Zachary Kessin

    My understanding is that a black hole follows the 4 classical conservation laws (mass/energy, Momentum, angular Momentum and charge). So its not that nothing can get out its a bit more subtle than that.

    My cat agrees with this statement, or at least he’s not saying anything while he watches me type it.

  42. Zachary Kessin

    Phil, you might want to look at google ads more carefully, you seem to keep getting real bozos I got this one on your page today: http://www.aethertheory.co.uk/

    Just goes to show that there are more kinds of idiots out there than we thought. Someone still belives in the Eather, who knew.

  43. Gary Ansorge

    As a musician once said,
    ” Small wheel’s turned by Fire and Law.
    Big wheel’s turned by the Grace of God.
    Every time that wheel goes round,
    Ya know we’re bound to cover just a little more ground.”

    Also, as far as the natural tendency of the universe to expand, all I have to do to affirm that idea is to look at my waist line,,,

    Gary 7

  44. PK

    No information transfer can cross the event horizon of a black hole (i.e. the boundary between inside and outside). This is independent from the conservation laws.

  45. Flingle Bird

    If by redshift we might ‘look into the past’, can we not look into the future conversely? I mean, if some matter from the galactic soup condensed before that which condensed to form our galaxy then mustn’t other galaxies have existed in the universe before the Milky Way? And granting that other galaxies did exist before ours, wouldn’t it be right to think that, since they’re older, they exist in the ‘future’?

    The answer perhaps lies in the oddities (to us) that a quantum universe reveals.


  46. Irishman

    We’re certainly aware that there are things out there that we can’t currently see, that are farther forward in time than our vision. The problem here is the “arrow of time”, and the time lag inherent in translation. In other words, velocity has an inherent time component, and it is the passing of time that measures speed of movement, that makes it speed and not just distance and direction.

    That is why we cannot see into the future, only the past. We can only see things that have had enough time for the photons that make up the image translate to us across the distance between. Given that we experience time in a linear fashion, unidirectional, we have no access to the future that has not happened because it hasn’t happened. We have no access to the present that is too far away to reach us immediately. Only the past, as it was when the photons left to reach us while we’re looking now.

    Curiously enough, that makes looking at things further in the past difficult – we have to look farther away to see further into the past, because the light that we are seeing now left there at a particular time. If we weren’t looking ten minutes ago, we can’t see the light that passed us ten minutes ago that left that object when it did. Since the photons travel at a set speed and don’t take detours or hang out at the mall for a while before continuing on their journey, we can only see the particular set of photons that left at precisely the instant* accounted for by subtracting back the travel time for that distance from when we are looking.

    *For a given value of “precisely” and “instant”. Relativity affects our understanding of simultaneity enough that these terms are difficult to express. The calculation has to be modified to account for the relativistic relative velocity difference between “here” and “there”. YMMV. Some Assembly Required. Warranty not valid in states where not legal. See your local Universe dealer now.

  47. Flingle Bird

    Thanks for enlightening me in your answer to my question, Irishman.


  48. There is no need for a cosmological constant if people realize that the observed Red Shifts do not measure the receeding velocity of stars and galaxies. In addition to the receeding velocity contribution by the Doppler shift there are three other contributions to the observed Red Shift – and they only depend upon the effects of gravity. General relativity described by Einstein shows that the energy and paths of photons are affected by gravity. The Red shift depends upon distance as shown by Hubble, but it was assumed (and never demonstrated) that it was due to Doppler effect. The reported gaps in the observed Red shifts are due to gaps in travel distance – there is no reason for gaps in the supposed expansion of the universe. THERE IS NO VAID PROOF THAT THE UNIVERSE IS EXPANDING. Thus no proof for the big bang, or need for dark energy, or the Accelerating expansion.

    Unfortunately this is a deconstructive contribution to the standard model of the universe – we have to start over, but it should be easier without the assumptions and mysteries.

    A related contribution to the new standard theory of the universe is the concept of Expanded Gravity which modifies Newton’s gravity so that it is also valid at galactic distances – without requiring Dark Matter.

    Do a Google search for inventing-solutions.com for more details.

  49. tomas

    How does Bell’s theorem of non-locality map to the observable universe? On the face of it, non-locality would seem to be expressed as the ubiquity of all spacetime events. In other words, a single point of origin located at the beginning of a perceived big-banging universe would be coincident with every conceivable point of perception, as well as with all intermediate points.

    If all spacetime events are indeed ubiquitous and coincident, then the notion of a spacetime continuum extending from a single point of origin located billions of light years in the past and a point of observation located here now is simply an intellectual convenience spawned by nodes within a cosmic neural net.

    Is it therefore possible that the appearance of accelerating cosmic expansion is a perceptual artifact? Perhaps more to the point, can any conception of a universe hosting perceivers be anything other than a perceptual artifact?

  50. Peter Gaffney

    Is time expanding in some way analogous to the expansion of space? If we talk about the expansion of space “accelerating,” doesn’t that imply that time is a fixed scale against which the rate of spatial expansion can be measured?

    It seems strange to me that we conceive of space and time as inseparable on a local level (e.g., in describing relativistic phenomena or the bending of space-time by mass) but when discussing the universe as a whole space and time seem to be treated as distinct from one another.

    It’s been mentioned that the expansion of space is only noticeable because gravity and the other attractive forces keep everything from galaxies right down to atoms (including ourselves) from expanding as well. Presumably there is nothing similar which would make the expansion of time — if it were indeed occurring — noticeable?

    Could the acceleration of the acceleration of the expansion of space be viewed as the acceleration of the expansion of time… and perhaps thus not so surprising? (Or is this “idea” either meaningless or just plain wrong?)

    I’ve read descriptions of black holes which talk about spatial dimensions becoming increasingly timelike as one approaches a black hole — at least in part because the future of anything lies more and more inevitably in the direction of the black hole. (I suppose you could say that here on Earth gravity makes the up-down dimension very slightly time-like, since the future of any object TENDS to lie in a downward direction — “What goes up must come down.”) This makes me wonder if what we see as the expansion of the universe could also be viewed as the dimension(s) of time becoming more space-like as we move away from the “white hole” of the Big Bang. I think it’s already widely believed that time ceases to be coherent if we try to conceive of anything “earlier” than the first few micro- or nano-seconds after the Big Bang — suggesting, I gather, that the “instant” of the Big Bang is something like a limit which can be approached but never reached. So is the expansion of the universe perhaps nothing more than the transformation of pure time into pure space?…

    …Okay, that sounds pretty inane, I’ll admit. But it DOES seem odd that time is considered the fourth dimension of a unified space-time, and yet — as I’ve said — concepts like the expansion of the universe are described as if they refer to changes in a three-dimensional landscape of space measured against a yardstick of constant time. (Likewise, discussions of the overall topology of the universe — as opposed to local distortions of space-time by gravity — generally seem to involve the shape of 3-dimensional space rather than the shape of space-time, as if there were no question of any essential curvature of time analogous to the question of the essential curvature/non-curvature of space.) IS time constant, or is it just convenient (as well as not misleading) to regard it as such?

  51. You are quite correct “ruidh”!

    Rangutan’s Theory: “Gravity is an observable resultant force.” Matter is bombarded from the cosmos by waves of energy from all directions. Like you suggest a cosmic wind like the solar wind. Close to large masses a very effective large force but radiation in free space from most directions weak but nevertheless causing an effect or motion. Our “gravitational constant” applies only to our inner solar system. Rangutan’s Hypotheses #18 (in this field): “Dark Energy in form of a continuos radiating micro energy has exited since the big bang and causes the universe to expand at an accelerating rate.” That is why the Voyager modules are escaping the solar system faster than predicted.

    Rangutan’s H#5: “All of our constants only apply to our small community, earth or inner solar system, in pure Science and Physics there are NO constants!” Like E=mc²

    [I need partners to help prove and present this new gravitational theory]

  52. Peter Gaffney asks can time be expanding. Here are some thoughts on that subject.

    To understand why it is necessary to assume that time cannot be expanding (or at least not expanding at the same rate) as the three dimensions of space, one must consider the following facts.

    1. The universe is expanding in, at least, three dimensions.
    2. The speed of light is constant (invariant over time.)

    To refute either of these is to commit secular heresy and doing so would expose one to the scientific equivalent of the Inquisition.

    What are the consequences of these assumptions? Let us assume that a distant galaxy is currently 100 light years away. At some time in the future it will be 120 light years distant due to the expansion of the universe. Here we are using the constant speed of light to measure the distance between two objects. If time expanded at the same rate as space then light would take the same interval to travel between the two galaxies in the future as it does currently. If this were so, then by definition, they would be at the same distance, ergo – no expansion, invalidating our first assumption. (Of course, one could just as easily imagine that time is contracting and space is stagnant!)

    Therefore, one must assume that there is at least a difference in the rate of expansion of space compared to that of time. This leads to several interesting speculations, not the least of which is an explanation of the unidirectional nature of time. Consider a universe of at least four identical and orthogonal dimensions having the following two constraints; it is expanding in three spatial dimensions through the fourth as explained above and, as three dimensional beings, we cannot directly experience properties outside the dimensions of space. Time, therefore, is not the fourth dimension itself, which we can’t experience, but our perception of movement within it. Since this movement is the result of the unidirectional expansion of the three dimensions of space within the fourth, our perception of time is therefore unidirectional. (For a lighthearted discussion of this concept, see http://www.melino.org/fractured_physics/index.html)

    Another interesting speculation that arises from this model concerns the nature of dark matter and dark energy, neither of which we can measure directly but only infer from their gravitational and expansionary effects respectively. The analogy of an expanding balloon has often been used to help visualize the expanding universe in which a single two-dimensional surface of a sphere expands outwards from a point representing the big bang. In this model the big bang is a single event resulting in a single universe. We can just as easily imagine an onion rather than a sphere with, not one big bang, but a continuous creation of layers (parallel universes?) occurring at the center. While we can’t have direct knowledge of any of the physical properties of any layer other than our own, we may infer their existence from their cumulative effect on our layer. Thus, the dark matter that is hypothesized to explain the missing gravitational effects in our universe may be nothing more than matter existing in other layers.

    Interestingly, all sorts of possibilities arise by changing the topography of the time dimension. A hyper-spatial Klein bottle for example (http://alem3d.obidos.org/i/kbottle/kbc1.png ) would continuously recycle universes. Each would originate in a big bang, expand outward for a while then collapse inward towards its origin in a big crunch. The changing curvature of the bottle could even be used to explain the inflationary expansion of the universe that is hypothesized to have occurred in the early universe.

  53. dmlex1

    “Is it therefore possible that the appearance of accelerating cosmic expansion is a perceptual artifact? Perhaps more to the point, can any conception of a universe hosting perceivers be anything other than a perceptual artifact?”

    Another proponent of the Strong Anthropic Principle speaks

    on another note:

    I can easily vouch for the variability of time – The year from my 15th birthday until I got my drivers license was easily 3 years long, the year from my 39th birthday until my 40th birthday was only weeks. Two weeks at the beach is easily only one half the time as one week at work.

    See this spacetime is not so hard to understand


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