NEWS: Dark energy stunts your growth

By Phil Plait | December 16, 2008 11:00 am

What the heck is dark energy?

We still don’t know. We’re pretty sure it exists; several independent observations indicate that the expansion of the Universe is accelerating. We’ve known for almost a century that the Universe is getting bigger, but in 1998 it was discovered that the rate at which it expands is itself getting bigger every day. Whatever is behind this is acting almost like anti-gravity, or more accurately a pressure that is making the Universe inflate faster every second of every day.

The galaxy cluster Abell 85 (optical image on left) is infused with million degree gas that gives off X-rays (right). By measuring the amount of this gas, astronomers have determined that dark energy exists and that it’s a constant throughout the cosmos. Not bad from a pink blob. Credit: NASA/CXC/SAO

But we don’t know what the heck this stuff is. We’ve hung the name "dark energy" on it, but we know very little about it. For example, is it a constant across space, with a strength that never changes with distance or time? Or is it a function of space itself? If it’s the latter, that means it gets stronger as space itself expands. That is, if there is some amount of dark energy in every cubic centimeter of space, and there are more cubic centimeters of space as the Universe expands, then dark energy will get stronger as time goes on. That means the acceleration will accelerate, growing ever-more until the Universe tears itself apart!

We’re talking here about determining the eventual fate of the entire Universe. Obviously, there’s some interest in this topic.

And now astronomers have found a new way to measure dark energy that may be able to differentiate between the two contenders. When the Universe was young, matter started to coalesce by gravity, forming huge structures millions of light years across. These collapsed to form galaxies and clusters of galaxies, like cities composed of thousands of smaller towns.

If the Universe were not expanding, forming clusters would be easy. As time went on, more matter could fall in to the cluster, forming more galaxies and making the cluster bigger. But since the Universe was expanding, there was a limit to how big the clusters could get; the outermost fringes would be moving away from the central regions, and that limited the amount of raw material available to make galaxies. It’s like going to the grocery store and trying to fill your cart with cans of spaghetti sauce, only to find workers removing the cans from the shelf at the same time. The number of cans you wind up with depends on how quickly the grocery store clerks are unshelving them.

So the sizes of clusters today depends on how quickly the Universe expands, and this cosmic expansion depends on the amount and flavor of dark energy infusing it. Aha! If we carefully study the sizes of clusters in the near and distant Universe, we can get a handle on dark energy!

That’s just what Alexey Vikhlinin of the Smithsonian Astrophysical Observatory and his team did. They examined the hot gas in more than a dozen clusters with the Chandra X-ray Observatory. The gas is the raw building material of clusters, and can be used as a tracer for how the clusters formed and how big and massive they are now.

What they found is, to me, something of a relief. First, they confirmed that the growth of clusters is consistent with the presence of dark energy in the first place (some people still doubt that dark energy exists, but this is another nail in the coffin of any alternative hypotheses). Second, they found that their results indicate that dark energy is a constant throughout the Universe. That is, it is not growing in strength with time, and the Universe won’t rip itself to shreds in the dim future.

Phew!

I’m impressed with this work. One good thing about it is that it’s independent of any other measurements of dark energy that have gone on before. We’ve been using things like distant supernovae to measure how fast the Universe is expanding; that’s how dark energy was discovered in the first place. Other studies have looked at the pervasive microwave glow of the Universe, and other indicators have been used as well. This is the first to use the hot gas in clusters, and it doesn’t rely on these other methods. That makes scientists more confident the result is correct.

Not that we really understand dark energy yet. We can measure its effects, but we don’t know what the heck it is. The most recent work is also bothersome: it indicates that the amount of dark energy in the cosmos we measure is 10120 times smaller than it should be. That’s a bit off! Obviously, there is something we’re missing, and many people suspect that there are extra dimensions to the Universe that we cannot see, and this may be the problem (it may also explain why gravity is so much weaker than the other three fundamental forces, but that’s another story…).

The good news is that this new work with clusters may shed some light on dark energy, and on the very nature of the Universe itself. But to me, there is more good news… What all of this is telling us is that the Universe is even more complex than we thought. That makes it more interesting, more cool, and more fun! There’s so much more left to learn, and the path to that knowledge is where the adventure lies.

Comments (94)

  1. I’m sure some wooist will see this as proof of something totally unrelated. Maybe it’s proof that bigfoot stepped on a strangelet, and it mixed with his toejam and made a grey alien abduct an eviscerated cow with the astrological sign of scorpio predicting the expansion rate of the universe caused by the LHC activating on a Friday the 13th…

    Sorry, I can’t even make up silly stuff that sounds sillier than the wooists stuff… I fail.

  2. JoeSmithCA

    I think we should call it Mystery Matter, just like Mystery Meat. The can is the known universe and whats in the can is…something. Maybe the rest of the universe is filled with Spam!
    ;)

  3. The heck with the Higgs-Boson: Whoever figures out Dark Matter, and/or Dark Energy will revolutionize our view of the universe itself.

  4. OtherRob

    If the Universe were not expanding, forming clusters would be easy. As time went on, more matter could fall in to the cluster, forming more galaxies and making the cluster bigger.

    Just a Liberal Arts major thinking aloud here, but… if the universe were not expanding, wouldn’t we just end up with one super-duper galaxy or galactic cluster?

  5. TheWalruss

    Goodness, how I love this stuff!

  6. TobiasTheVIkign

    I don’t think i get it.. There are to points of this blog entry that apparently can’t coincide inside my head.

    A) scientists have measured Dark Energy, and can say that our universal expansion isn’t accelerating.
    - I seem to remember that universal expansion is accelerating.
    - The sentence above says that the force of Dark Energy is a constant.
    - Though, it does say “dim future”, so maybe the changes in acceleration aren’t the same… ?

    B) The same study indicates that the force of Dark Energy is 10^120 times smaller than what it should be.
    - Does that mean that it is 10^120 times smaller than other studies(using background radiaton, or type 1 super novae?)
    - Does that mean that with it being 10^120 times smaller the universe won’t tear itself to bits in the “dim future”
    - Does it mean that if it was 10^120 stronger the universe wouldn’t tear itself to bits in the “dim future”

    I mean.. if B is true(the effect measured being 10^120 time smaller than what it should be) how can anything be extrapolated from it?

    Maybe i’m just really dense.. but i don’t get it.

    Can anyone explain it to me?

  7. TobiasTheViking

    Ok, i did a more careful reread, and saw that i misunderstood a part.

    Basically, i get part A of my question now, that was just lazy reading on my part.

    Part B is still puzzling me though.

  8. Bill Nettles

    I’m with you, RapidEye,
    I just want to be around when they do. That would be like being a physicist in the 1895-1925 decades.

  9. “Just a Liberal Arts major thinking aloud here, but… if the universe were not expanding, wouldn’t we just end up with one super-duper galaxy or galactic cluster?”

    That was one of the commonly excepted old theories: our expansion would slow, then reverse, until it all came back together in a “Big Crunch”.

  10. Todd W.

    [electric universe rant]This new finding is clearly flawed, because that isn’t gas, it’s plasma. Sheesh! Two-bit hacks.[/electric universe rant]

    Seriously, though, this is cool! Now we just need to figure out what the heck DE (and DM) is!

  11. Sir Struggle

    Wouldn’t this energy use the same principles as an ion engine? It doesn’t take much energy to cause acceleration in space, especially to an object already in motion. Therefore a very SMALL force applied constantly will eventually lead to higher and higher speeds in a non-drag environment. Could it be that many scientists are looking for something that will turn out to be way smaller than they think it is?

  12. “That would be like being a physicist in the 1895-1925 decades.”

    Agreed. Astronomycast this week has a good discussion about how Robotic Sky Survey’s are revolutionizing astronomy. Between computer power, gigapixel cameras, and adaptive optics, we are on the cusp of a light year jumps in our ability to understand the universe around us. I hope it is enough to get the dark matter and/or dark energy issue sorted out.

  13. IVAN3MAN

    Dr. Phil Plait:

    It’s like going to the grocery store and trying to fill your cart with cans of spaghetti sauce, only to find workers removing the cans from the shelf at the same time. The number of cans you wind up with depends on how quickly the grocery store clerks are unshelving them.

    Yeah, I know what you mean, Phil. Just when one has got used to the layout of the bloody grocery store, they then go and move things around again so that you have to spend twice as long doing the weekly grocery shop because you’re searching for the bloody item(s) that you want. It’s a ploy by the grocery stores to confuse customers in order to entice them with “special offers” — things that you don’t need!

  14. Cheyenne

    Every discovery opens up new questions. Crazy universe this is. Fascinating stuff.

  15. Mike

    What they found is, to me, something of a relief…the Universe won’t rip itself to shreds in the dim future.

    You were worried about that, were you?

    OK, enough of the snark. Doesn’t this fact: The most recent work is also bothersome: it indicates that the amount of dark energy in the cosmos we measure is 10^120 times smaller than it should be. call this whole result into question?

  16. Todd W.

    @IVAN3MAN

    I knew it. The grocery workers’ union is behind the expansion. And the big bang was one of their ilk dropping a can of green beans on the floor of aisle null.

  17. Charles Boyer

    What’s on the “other side” of the boundary of the universe? If it is expanding, it would seem that there is an edge to it – and that there is an “other side” to the edge.

    Is there a there there? Or is it literally nothing — no time, n0 space, no fun, no women, etc.?

    Serious question.

  18. Bystander

    “You were worried about that, were you?”

    Come on now ;) You mean to say that you don’t care what eventually happens to ‘it all’? You don’t imagine crazy things like our species populating new galaxies and surviving the eon? I wonder if we’ll still look the same after another 100k years… yeah 100k years isn’t exactly far into the future of everything but my imagination only goes so far before spazzing out. ^_^

    “(it may also explain why gravity is so much weaker than the other three fundamental forces, but that’s another story…)”

    I like your stories and the way you think. Please tell :D

  19. Todd W.

    @Charles Boyer

    We may never know. IIRC, from one of Phil’s previous posts, the universe is expanding faster than the speed of light. So there is a horizon beyond which we can’t see, meaning we can never see any edge. Also, Phil has said before that the universe is more like being on the surface of a balloon that is inflating. There is no edge (and no center, really), but everything in the universe is getting further away from each other, generally speaking.

    Someone please correct me if I got any of the wrong.

  20. Mike

    @Bystander: Intellectually, I care a great deal. Emotionally, I couldn’t care less. Won’t be here. Neither will “anyone” else. Tens to hundreds of billions of years is a LONG time.

  21. 10^120 smaller than it should be? I mean, that’s a lot. A lot. That’s way way way off. Like, not even close. That’s like measuring the mass of something at 1 gram, then measuring it again to make sure, and finding out it masses at 1,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 universes.

    I’m having trouble imagining any sort of measuring system where one result is that far off from another. Is that a typo?

  22. @Todd W: Sounds right to me. There is a boundary of sorts that we can’t see beyond because of the finite speed of light and age of the universe, but there is no hard edge to spacetime itself.

  23. Helioprogenus

    Carey, I don’t think that’s a typo. There are so many variables in these instances, that you’re lucky you have some number that makes sense. Imagine the trouble theorists have when inserting the equations of gravity into quantum mechanics. They come out with numbers so nonsensical, they make 10^120 look utterly normal. Seriously though, the universe is an awfully big place, and with so many variables to account for, any equation that is substantially off clearly needs further elaboration, and perhaps extrapolation. In this case, perhaps with string theory, rolled up dimensions, you can account for all that missing mass. Or perhaps, there’s something grander at work here, and we’re just scratching the surface.

    Incidentally, that really bright source of x-rays in the cluster seems to be centered on a particular non-symmetrical elliptical galaxy. I wonder if this is an extremely active galaxy, or whether the x-ray jets are pointing directly in our direction? I can clearly see other weaker x-ray knots that can correlate with galaxies, so perhaps these aren’t producing jets directly in our direction. Any ideas?

  24. “We are unfamiliar with plasma because we are blind to it. Modern astrophysicists are in this sense correct to claim that 90% of the universe is undetectable “dark” substances. Their error is to fill in the blank with mathematical extrapolations from familiar theories and to leave their thinking blind to plasma.” — Mel Acheson, physicist, December 2008

  25. Sili

    I still say we should just call it “It”. The Universe has ‘it’. It’s the ‘it’ Universe.

    That said, a discrepency of 120 orders of magnitude makes me rather reluctant to say that we now know for sure that ‘it’ is there. (No, I’m not a denier – and I lurrrrve Dark Matter.)

  26. DrFlimmer

    @TobiasTheVIkign

    This “little error” is between (all) measurements and a (very easy ;) ) theory of a quantum gravity. So, this theory is probably wrong ;)

    @Charles Boyer

    This question is more a philisophical one than a physical one. Einstein’s GR explains our universe from “inside”. It does not look from the outside on our universe (as we look on a ball), it describes the “ball from the inside”. We are “in the ball’s surface” – hard to imagine, something like that ;) . So a physicist can never answer “what is outside”, we don’t know, we will never know. Btw: This question I used to ask myself when I was about twelve years old – that brought me to physics what I am studying right now ;)

    Btw: I know what Dark Matter is, and so does everyone here ;) Just watch Star Wars (renamed as Episode 4) and listen to Obi Wan. He’s telling Luke something like:

    “The force is an energy field. It surrounds us, it penetrates us, it binds the galaxy together”

    Do I need to say more?

  27. As far as the universe expanding faster than the alleged constant c that is nonsense like the rest of the so-called “science” that emerged in the first half of the 20th century.

    Redshift does not signify recession. Hubble’s assistant Arp has shown this beyond any reasonable doubt.

  28. undercover

    Why do they have to delay the L.H.C. restart-up so much?

  29. IVAN3MAN

    Todd W.: “Someone please correct me if I got any of the wrong.”

    I think that should be “this”, not “the”. :-)

    Oh, and it wasn’t a can of green beans being dropped on the floor that started the Big Bang. It was God after eating a plate-full of baked beans — Blazing Saddles camp-fire scene — that did it!

  30. OtherRob

    That was one of the commonly excepted old theories: our expansion would slow, then reverse, until it all came back together in a “Big Crunch”.

    Thanks, RapidEye (I almost typed RabidEye :-) ). that helped a lot.

    Personally I don’t think Dark Matter is invisible, I just think it’s really shy…

  31. JLF

    I dislike it when people pull out the 10^120 number, for exactly the reason we see here — people think that there’s some real theory that contradicts the observation. The 10^120 comes from a very simplistic calculation of vacuum energy density, and we’ve known that it’s wrong for longer than we’ve known that dark energy exists, simply because such a huge vacuum energy would mean a universe that instantly ripped itself apart. The question used to be why that value was zero; now the question is why does it have the (small) value that it does. Since physicists have been able to calculate away much larger discrepancies (like, say, factors of infinity) in their theories in the past, I’m not too worried about the current status of an area where the theory is still very immature.

  32. onshay

    You know, I was watching “The Universe” on the history Channel before leaving for work this morning and, by coincidence, the topic was Dark Matter (is this the same as Dark Energy?). Now I am certainly no expert in this area though I do consume the contents of this blog like I do Jelly Bellys and there was something said on the History Channel this morning that confused my simple mind.

    It stated that Dark Matter is invisible, accounts for the majority of the mass in the universe, but it does not bend light. I was hoping that someone out there could tell me why Dark Matter is massive enough to greatly influence the movement of everything we know and observe through space but does not bend light as other massive cosmic entities do.

  33. Charles Boyer

    If the Universe is expanding faster than the speed of light, is that not a violation of the Special Theory of Relativity? Or would STR not apply at “the edge” because beyond the edge there is no space nor time therefore no need for the unification of the two as spacetime until it is within the Universe?

    The mind boggles.

    Seems to me that there is a there there and there must be something there even if there is nothing there.

  34. Charles Boyer

    Oh and I hit submit too quickly to say thank you to those of you who took the time to try to explain this to me. I have an engineer’s education in physics, but the truly big question leave my head swimming as though I had a bit too much to drink. I really appreciate your thoughtful replies.

  35. Charles, you are correct about Special Relativity being violated. If the universe is expanding faster than c as the mainstream fundamentalists claim, then you should discard Special Relativity. However the universe is not expanding faster than c because redshift does not signify recession (See Halton Arp). However, there are important reasons Special Relativity is in the garbage can. There is no such thing as nonbeing, void, empty space, or a vacuum except in mathematical imagination therefore there is no constant c. Space is full of plasma.

    “The first decade of space research mainly concentrated on the exploration of space near the Earth: the magnetosphere and interplanetary space. These regions earlier were supposed to be void and structureless but we now know that they are filled with plasmas, intersected by sheathlike discontinuities, and permeated by a complicated pattern of electric currents and electric and magnetic fields.” — Hannes Alfvén, physicist, 1970

  36. DenverWorkM

    Im going to settle this thing for you guys once and for all. In the beginning, God created the universe. When he was done, he ripped off a Gigantic fart, opened a Corona Extra, and then sat in his lawn chair to watch the entertaining results for the next couple billion years. All this dark matter and dark energy is the fart leftovers.
    I know this is a skeptic site and you’re going to want proof. When we are capable of travelling into one of those dark matter zones, just stick your head outside the starship and sniff. There’s your proof!
    You think Im nutz? HA! You’ll see, I’m right. I’m not crazy…
    Hey wait, who are these guys in the white jackets? Phil, did you call them? Hey! get yer hands off me! Whoa, this guy has a needle the size of a shotgun barrel…what are you doing with that thing…OOOwwww!
    Lemme go! I aint done nuth…errrr….zzzzzzzzzz

  37. Cheyenne

    Charles – It’s not a violation of relativity because it’s space itself that is expanding. You can’t transmit information, or light, faster than c, but you can create new space at a rate that is faster than light. What we can see is the boundary edge (to us) but the universe is certainly bigger than what we can see. With every passing day we can “see” a bigger universe as those photons can finally hit us.

    Hope I didn’t completely mangle that up…..and I know there’s a heck of a lot more to it.

    And regarding the universe itself- “It’s turtles all the way down!” (Phil’s first book- I think).

  38. Cheyenne, according to special relativity, space cannot move faster than the speed of light.

  39. Mike

    Cheyenne, according to special relativity, space cannot move faster than the speed of light.

    Wrong, but thanks for playing.

  40. Mike

    I seem to remember that when the expansion of the universe was first shown to be accelerating, a calculation was done to see if “dark energy” could be explained as quantum flucuations of the vacuum, but that the magnitude of that source was too small by 10^120.

  41. JT

    Cheyenne, according to special relativity, space cannot move faster than the speed of light.

    Wrong. According to special relativity mass cannot move through space faster than the speed of light. It does not place any restrictions on the ability of space itself to expand.

  42. Mike

    Thanks, JLF, I just read your comment.

  43. Andrew

    Electric universe troll is electric! *doot doot doot doo-doot doo-doo-doo doot doot*

  44. Or would STR not apply at “the edge”

    There is no edge to spacetime. However, the lightspeed limit applies to objects in spacetime, not to spacetime itself, so the expansion can go faster than light.

    space cannot move faster than the speed of light.

    I don’t think the expansion is characterized as motion.

  45. Todd W.

    @Charles Boyer and OIM

    Note, the individual objects in the universe (planets, stars, galaxies, etc.) are not moving faster than the speed of light. It’s hard for me to wrap my head around, as I’m not an astrophysicist, but that’s how Phil explained it.

  46. Todd W.

    @OIM

    It has been pointed out several times before in other posts that Halton Arp’s whole redshift thing has been discredited and is severely out of date, as far as current research goes.

    Say, are you that same electric universe/plasma guy that was posting a couple months ago, just using a different name?

  47. Mike

    But I took Phil to be saying that the Vikhlinin result was 10^120 off, which I took to be a remarkable coincidence, and the reason I brought it up. (“The most recent work is also bothersome: it indicates that the amount of dark energy in the cosmos we measure is 10^120 times smaller than it should be.”) Presumably, “the most recent work” is the Vikhlinin result. What gives, Phil?

  48. Charles Boyer

    There is no edge to spacetime. However, the lightspeed limit applies to objects in spacetime, not to spacetime itself, so the expansion can go faster than light.

    space cannot move faster than the speed of light.

    I don’t think the expansion is characterized as motion.

    If there is spacetime, and not-spacetime that the Universe is expanding into, then the suggestion would be that there is an interface, right? There would be a point where spacetime is, beyond which it isn’t there. That’s what I would label an edge.

    In other words, if the universe is expanding, then there must be a not-a-universe it is expanding into. Entropy in reverse, perhaps.

  49. Mike

    In other words, if the universe is expanding, then there must be a not-a-universe it is expanding into.

    Hard to imagine, but no, there isn’t.

  50. Ben

    Count me as a member of the group confused by the ’10^120 times smaller than it should be’ statement. So, I did some additional reading of the news releases related to this new dark energy study, and here is my attempt to sum it all up.

    First of all, the 10^120 does not come from this new study at all, but instead from physicists attempting to explain what dark energy is (see Lambda-CDM model, which just happens to have a cosmological constant value of 10^−120 in reduced Planck units). In other words, we think there is a LOT of dark energy in the universe (current estimates are that it makes up 74% of the universe), but it is not having that big of an influence on things, so it must be a really weak force. Physicists already do not like gravity, since it is so much weaker than the other fundamental forces (and also because gravity refuses to easily be constrained by a ‘theory of everything’), but now you have this new dark energy force, which is many, many orders of magnitude smaller.

    Getting back to the new study, it is my understanding that the number of clusters they have studied to date is not statistically significant enough to say anything for certain about the expansion of the universe or dark energy (their measure of the equation of state parameter is -1.14 plus or minus 18%). But, it does show that the far clusters (earlier in time, of course) are larger than closer clusters by about the amount predicted by the ‘cosmological constant’ theory of dark energy, and when combined with other studies they think they have narrowed the equation of state parameter down to -.99 plus or minus 8%. However, because of the assumptions that are necessary for performing any astronomical study, additional analysis of cluster sizes along with other research may still show that Phil’s worst fears are true after all, and there is an acceleration of the acceleration of the expansion of the universe. It may even turn out that my worst fear is true if some day we discover there is an acceleration of the acceleration of the acceleration of the expansion!

    By the way, click on my name for a link to the actual 15 page paper by Vikhlinin and his cohorts.

  51. then there must be a not-a-universe it is expanding into.

    No, there’s no “outside” of the universe, and space is not expanding into non-space, which wouldn’t even make sense really. Unfortunately, I don’t know how to explain that with an analogy; the balloon analogy fails for this one, IMO, but it’s the best I’ve seen.

    Our intuitive grasp of “expansion” fails when talking about spacetime expansion. The universe is not a sphere being inflated, with a single point at the center, and inside and outside, and a well-defined boundary. I don’t claim to understand it myself; I don’t know the math. I can only tell you what I’ve learned from others over the decades.

    Here’s a link that does better than I can, but it’s best to get a proper book to learn about this topic.
    http://brahms.phy.vanderbilt.edu/~rknop/blog/?p=28

  52. Davidlpf

    @Todd, I hope it is not Mr Meyers again.

  53. Hax Or

    Guess why scientists are ignored by most people? Comments like this one: “We’re talking here about determining the eventual fate of the entire Universe. Obviously, there’s some interest in this topic.”

    Your lifespan vs. the universe timetable is way too disparate to take you seriously.

    But it’s comments like this that make ‘normal’ folks (aka non-scientists), think you have lost your marbles.

  54. Phil, or anyone else…
    I watched a video concerning the Hubble Deep Field image the other day, and the narrator made the comment that the Universe is 78 billion light years across. Maybe you’ve explained this before, but I always thought it was 15 Billion LY across?

  55. TheWalruss

    It seems to me this is actually more important than it seems.
    Currently, space is expanding at such a rate, that the amount of stuff in the observable universe is decreasing. Yes, the observable universe is increasing in volume at the speed of light in all directions in all dimensions, but SPACE is being stretched such that light emitted from a galaxy “currently” at the horizon will never reach us.

    Ever.

    If space stopped expanding at this rate, then we’d eventually have the chance to see this galaxy once again. If, on the other hand, it expands, and if it expands faster and faster, then, in a few billion years, our universe will be very small indeed. And we might end up alone, after all.

  56. Mike

    Hax Or Says: Be grateful for scientists. Without them, “normal people” like you would still be clubbing wart hogs over the head to get meat for dinner.

  57. @TheWalruss: And we might end up alone, after all.

    And then it gets worse.
    http://www.space.com/scienceastronomy/big_rip_030306.html

  58. Ja Muller

    Back to the 10^120 thing.

    The number you get from standard quantum field theory is a factor of 10^120 too large. People knew that this calculation was off from day 1 since a value that large would not allow the universe to look anything like what we see. It was thought that the real value is exactly zero, which fit in with all data at known at the time. This seemed reasonable since many supersymmertic versions of quantum field theory predict it to be exactly zero. The fact that it is not exactly zero and not much much larger is a huge problem that we can’t solve presently.

    I should point out that Steven Weinberg was able to guess that the value of the cosmological constant could be small, but not zero based on the anthropic principle and some sort of unobserved multi-verse. This is of course very controversial and it is unclear if Weinberg just got lucky or is on to something real.

  59. Ja Muller

    @JFL

    “I’m not too worried about the current status of an area where the theory is still very immature.”

    I peronally am a bit worried about this. I would PREFER if it was calculated to be infinity since that is a clear sign that you are doing the math wrong. But here, we have an amazingly successful theory that is wrong for some reason. It is unclear if any experimental data will come in the near future to help with this either. Ed Witten has also publically stated that he is starting to wonder if humans are smart enough to understand the universe which is not a good sign :)

  60. Torbjörn Larsson, OM

    Nice independent confirmation. And some of the press releases mentions another study in optical light that arrives at the same conclusion (with poorer statistics), so the observation seems sound as well.

    if there is some amount of dark energy in every cubic centimeter of space, and there are more cubic centimeters of space as the Universe expands, then dark energy will get stronger as time goes on. That means the acceleration will accelerate,

    In other words, the universe doesn’t behave as a total jerk.

    ["Jerk" being the next (4th) derivative of position, after acceleration.]

    according to special relativity, space cannot move faster than the speed of light.

    I love then troll says that! As the only framework where you can model this is AFAIU general relativity, which IIRC obeys special relativity locally. So they deny the science they argue from, or accept what they argue against, or… : from a logical error you can derive anything.

    I seem to remember that when the expansion of the universe was first shown to be accelerating, a calculation was done to see if “dark energy” could be explained as quantum flucuations of the vacuum, but that the magnitude of that source was too small by 10^120.

    AFAIU JFL has it right, the vacuum as a source of energy density is naturally (i.e. simplistically) too large by 10^120. (And really, really inconsistent with what we see, as opposed to dark energy observations.)

    dark energy force

    I get my fingers smacked when I say that gravitation is a force. It isn’t seen as a force in GR, AFAIU gravitation curves spacetime which objects travels freely in straight lines (as they observe it locally).

    So I will nitpick that dark energy presumably isn’t a force either: it affects spacetime, not directly the objects in them.

  61. Torbjörn Larsson, OM

    D’oh! Excuse my obvious speling mistakkes and missing – nap time, perhaps.

  62. Ja Muller

    “I get my fingers smacked when I say that gravitation is a force. It isn’t seen as a force in GR, AFAIU gravitation curves spacetime which objects travels freely in straight lines (as they observe it locally).”

    Gravity is as much of a force as the electricity or the strong force. It comes from the exchange of a spin 2 boson, the graviton. The fact that you can describe the low energy effects of gravity well as a simple geometric thoery is irrelevant.

  63. To those who don’t understand the Special Theory of Relativity,

    According to Albert Einstein, no object can travel faster than the speed of light.

    Therefore if you say space can travel faster than the speed of light, then you are conceding that space is not an object.

    Therefore space does not exist.

  64. JoeSmithCA

    ether : A hypothetical medium formerly believed to permeate all space, and through which light and other electromagnetic radiation were thought to move. The existence of ether was disproved by the American physicists Albert Michelson and Edward Morley in 1887.

    Hmmmm…

  65. JoeSmithCA

    Forgot my smiley face denoting my typical (almost) never serious tone :) Don’t take my dictionary post about ether seriously :)

  66. Ben

    @Torbjorn

    Jerk is only the 3rd derivitave of position (since acceleration is 2nd and velocity is 1st). Jerk is not really used much, but is usually called jolt in Britain (surge and lurch and a whole bunch of others have been used for this 3rd derivative throughout the years by various people). Some people have proposed using snap, crackle, and pop for the 4th, 5th, and 6th derivatives of position. But of course, since we understand derivatives, there really is no reason to name these higher derivatives that do not get much use.

  67. Larian LeQuella Says:
    I’m sure some wooist will see this as proof of something totally unrelated.

    Right here, nonetheless… [we know to whom I'm referring]

    JoeSmithCA Says:
    Maybe the rest of the universe is filled with Spam!

    Did you just check your e-mail before posting? :)

    “Dark Energy is the Flying Spaghetti Monster’s pasta sauce, Dark Matter is the cheese topping”
    -John Paradox

    J/P=?

  68. slang

    To those who don’t understand the Special Theory of Relativity,

    Damnit. Another irony meter blown to hell.

  69. quasidog

    Great post Phil. Love this stuff. The universe is too beautiful to rip itself apart anyway .. hehe jks.

    Something has always set off warning bells in my mind whenever I hear certain facts about the so called ‘dark energy’. Not that I have a physics backround or anything, but the explanations so far just haven’t felt .. right. I get a funny feeling it will be a fair bit longer than many believe when we even get close to understanding this. Like centuries … or more.

    I like the idea of it being more ‘complex’. Complex means more facts and more mechanics. So far it has seemed a little presumptuous to think with the little number of facts that help to describe it, that we could somehow soon understand how it all works, or what it even is. Like .. um .. way back when they thought they knew what gravity was, and even after Newton it still wasn’t exaclty right … and then Einstien and it’s still missing stuff ! (facts) …. and we still don’t get it!

    Gravity times about… a billion !!!, in terms of actually understanding it I reckon. I am exaggerating of course, but I hope you know what I mean. Something tells me we are only just scratching the surface …. but we don’t even know where the surface is, or how we are scratching it. ;p

    Astronomers and physicist are gong to look back and laugh at certain scenarios we had about the effects of dark energy .. and what it is … if it even is. I mean … it could be a bunch of forces combining to look like one big force. I mean .. some of the ideas that were around 100 years ago about our universe look downright stupid now, but that’s because they had less facts, and made guesses based on those facts. There are always going to be scientists though that think they are on the verge of understanding it all. For various reasons. That’s a fact.

    Nar … we are not even close . WOOT !

  70. Gary Ansorge

    AH, you’re ALL wrong,,,there is NO expansive force,,,we’re all just swirling down a deep rabbit hole, space/time twisting and curling, being stretched by gravity’s well. Close up, there is no obvious elongation. Far away, we see the effects of the stretch,,,so it’s just the gravity stretch,not a mysterious dark energy push,,,

    There now. Doesn’t that make Y’All feel better? ,,,or, as Randi might say,,,it’s ALL illusion,,,snark,,,

    OilsMastery: Never confuse mass(dictated by the Higgs boson) with space/time(gravity itself, curled around the Plank length),,,mumble,mumble,,

    As a famous scientist once said, ” What is so strange is that humans(with their finite colloidal brains) can understand the universe at all,,,”

    ,,,or not,,,but we won’t know which it is until we’ve given up trying, if we ever do.

    Then, of course, there’s the cosmological constant, one of the most famous fudge factors in history. A natural force that is not defined but acts as it damn well pleases,,,kinda like my ex-wife,,,

    Gary 7
    PS I note there are at least two different types of brains,,,one which wants everything nailed down, all the Is dotted and the Ts crossed,,,then there is the other type, which hopes the universe actually IS infinite, with something left to learn, forever,,,Ah, ambiguity, thy name is fascination,,,

  71. DrFlimmer

    “According to Albert Einstein, no object can travel faster than the speed of light.”

    I agree.

    “Therefore if you say space can travel faster than the speed of light, then you are conceding that space is not an object.”

    Definitly space is not an object, have you ever seen space or hold it in your hands? I didn’t.
    BBT tells us that:
    During the BB spacetime itself popped up. And since then in every m^3 “new” space is generated. We don’t feel it because some forces out there bind us togther. But if there is no force at hand that can prvent “objects” from ripping apart, spacetime will grow. So between galaxy clusters, where gravity is weak, space can grow. And it does, as we see.
    And as farther away an object is from us as more “space” can grow, as faster it seems to expand. So finally since space is not bound to STR it seems to grow so strongly that the light-emitting objects are “moving” away from us with more than c.
    But those objects aren’t moving with respect to us as we would think of a “move”. It is space itself that expands and the galaxys are just some dots in it, glued to its positions if you like (not exactly, but you get the point).
    This also means that we get a curtain. Galaxies beyond the threshold of the expansion rate being equal to c are invisible to us because light cannot reach us. Therefore the universe we can see is not the whole one, but only the part up to that threshold. Being 13.7B years old the threshold has moved to a point 13.7B LY away from us – although the universe is much bigger (someone mentioned the number…).

    “Therefore space does not exist.”

    It does, same as you. But since I based my argumentation on BBT, which you deny, you will not accept what I’ve written…..

  72. we’re all just swirling down a deep rabbit hole

    Oh, pellets! Unexpected visitors! *hides his valuables*

  73. Gary Ansorge

    DrFlimmer:

    Oils LOGIC dictates consistency,,,unfortunately, the assumptions upon which it is based, determines truthiness(ie, applicability to reality).
    As in: We are composed of matter(ie, bosons) therefore anything not composed of matter,,,doesn’t exist,,,
    Excellent logic but the basic assumption is in error. Space/time is not matter. It is the field in which matter is imbedded. Mass is not an intrinsic quality of matter,,,it is the interaction of matter(thru the Higgs boson) WITH space/time.

    Naked Bunny: Yeah, we’ll ALL be visiting you,,,soon(read as sometime in the next 10^20 years,,,or so,,,) so clean up those dropped pellets, OK?

    GAry 7

  74. I wonder what the justification is for using the term “energy” as part of “dark energy”. All other forms of energy we know of can be transformed into matter and have matter transformed into them. If it’s really some type of energy in “dark energy” then the same should be true – dark energy should be capable of being trasformed into matter and vice versa. Is there any observational evidence of such transformation? I doubt it.

    I think it’s much more probable that what we’re calling “dark energy” is simply a geometrical effect caused by our observable 3-space being imbedded in a higher dimensional N-space (N is greater than 3).

  75. Todd W.

    @Tom Marking

    Maybe dark energy can be transformed into dark matter?

  76. Ja Muller

    Not all mass comes from interactions with the Higgs. If you turned off the Higgs mechanism, your mass for example, would be close to what it is now.

  77. @Todd W. “Maybe dark energy can be transformed into dark matter?”

    Maybe, but I’d like to see some evidence of that. Do you know of any?

  78. Todd W.

    @Tom Marking

    Hmm…there is evidence that dark matter and dark energy exist, and that they don’t interact well with “normal” matter or energy, ergo, they must work with each other like normal stuff works with normal stuff?

    Yeah…I got nothin’. :)

  79. Gary Ansorge

    Ja Muller: SO, I guess you’re not a fan of GUT theories??? The Higgs Boson is a postulated particle under certain GUTs that seeks to explain why matter has mass at all. MAybe the LHC will allow us to detect them(the Higgs)in the energy range for which it was built, thereby eliminating a slew of theories that either predict NO higgs particle at all or else a Higgs at a much higher energy range. IF the Higgs IS detected by the LHC(and I bet it will be) we will have a better grasp of the fundemental structure of reality,,or we’ll have to go back to the drawing board.

    GAry 7

  80. Vortmax

    As I understand it, space itself is not expanding faster than c at any given point. It’s the apparent acceleration over distance that grows to c or larger at the “boundary” of visible space from here. So every “block” of space is expanding at a rate of x, and something three blocks away from us would appear to be receding at a rate of 3x. Far enough away, and x>=c, and we can’t see any further.

    Something still bothers me about dark energy and dark matter. At this point, it feels kinda like epicycles used to explain the movement of the planets and such back in the dark ages. We know something is there, and we can measure its effects, but we still don’t know what it is. I think we’ll need a lot more data before we can even start to explain this.

  81. quasidog

    DJflimmer … um … I believe it was ….

    ‘no object WITH MASS .. can travel faster than the speed of light.’ You forgot to mention mass.

    Leave out enough facts and anything is true.

  82. Ja Muller

    @ Gary You misunderstood my post. The Higgs is clearly responsible for elementary particles masses, I was just pointing out that this is a small part of what makes up the mass of macroscopic objects.

  83. DrFlimmer

    quasidog:

    of course, you are right. I thought that “objects” would define a massive one, so since spacetime has no mass at all I didn’t consider it an object in this sense ;)

  84. quasidog

    Yeah Drflimmer, I was just thinking of a photon as an example of an object, that isn’t massive. Maybe there are other such non-massive objects making up, or interacting with space-time.

    Just a thought. I am no physicist.

  85. eddie

    Hmmm, thought provoking discussion.
    Some of the thoughts it provoked include;
    There’s good evidence for an accelerating expansion but this by no means has to be a cosmological constant. Proposals for other mechanisms most welcome.
    Anyway, if universe is gauge invariant, a cosmological constant is meaningless as you’d just be adding 10^120 to all points in a scalar field and not affecting the dymamics.
    Please not to misunderstanding to higgs mechanism.
    In standard model, you have exact symmetry, with all fermions having mass identically zero. Higgs serves to break this symmetry and get e.g. top quark heavier than strange, etc. Actual mass comes from coupling to inertia field, but quantum gravity not yet sorted.

  86. eddie

    Also, re ‘its all plasma’.
    Of course, a lot of it is plasma. That’s just gas atoms and molecules in which the electrons are separated from the nuclei due to high-energy radiation.
    The extra energy stored in plasma, over the basic gas, is well understood as electrical potential. This has a measurable gravitational effect and can be modelled by analogy with the displacement field on an electrolyte. It’s different from a cosmological constant, though, as it varies with the intensity of the radiation.

  87. Gil

    This is a little off topic. Sorry.

    I’ve heard many astronomical blogs and articles ponder and speculate a great deal over exactly what dark matter is. I understand it originates from the same place neutrinos did — a mathematical placeholder to make certain calculations work.

    I took an astronomy survey course in my first year at college, and through the course the prof taught us an overview of the commonly accepted and popular theories of the universe, including why a gravitational perspective of the physics that run the universe requires dark matter.

    On the last day of the course, he ran through several unpopular theories of the universe, including the opinion that most astrophysicists don’t use magnetism to explain the motions of galaxies, and how there was a small body of plasma physicists who claimed to be able to explain galactic spin through magnetism, which completely eliminates any need for dark matter.

    So why doesn’t anyone ever talk about this other perspective? Have these theories been proven false? Are they merely unpopular and thus never gain the attentions of the astrophysics community at large?

  88. eddie

    I have the inkling of an idea for a theory. No maths just yet, only a physical mechanism.
    It’s sort of like supersymmetry in that fermions change to bosons. It’s also sort of like quantum gravity in that the inertia field affects the behaviour of quantum particles.
    In short, it is that all free (unbound) particles behave as bosons; having zero rest mass and light speed, while when bound they act as fermions; with exclusion, etc.

    I’m thinking it explains why there was a short delay between us seeing light fron sn1997a and detecting neutrinos. If the neuts were massive fermions the whole journey, they’d have been much delayed. If they were massless they’d have arrived with the photons. Instead, they were massless bosons for most of the journey and acquired mass when they entered the solar system’s gravity field.

  89. Gil

    In response to eddie:

    The only problem with them being without mass until they hit our gravity field is that our gravity field exerts an imperceptible pull on all matter for a very great distance. In gravitic universe models, they model the gravitational effect of every particle on every [i]other[/i] particle.

    I understand that gravity data travels at light speed, but the gravity effect for the star and orbiting bodies would be rather similar for them in their current state or as a dust ball and dust rings, as the same quantity of mass-having particles is in question.

  90. eddie

    Thanks Gil, Just an inkling as I said. As well as the regular attraction, the particles would respond to threshold changes in field gradient by changing quantum state.

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