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Inflation or normal space/time misunderstood?

  1. Apr 9, 2010 #1
    Please forgive my ignorance but:
    I am trying very hard to understand how expanding space works.
    The problems I have are:

    1. If expanding space has enough "connection" (friction?) to pull galaxies apart then it should also have a resistance to planets in orbit, rockets continuing on their course after the engines quit firing, and all related free movement in space. (ballon example doesn't work - the dots are connected to the balloon and galaxies are free in space)

    2. "Red shift" and "time dilation" (perceived) is used to anchor this theory but can't that same red shift and time dilation be explained by the different densities of particles in the space between those great distances?
    When light goes through different media it can slow or lose energy. Could this cause the effects that we are measuring? If not why not?

    Keep in mind that I am just a 60 year old man trying to understand this. I have spent time looking at many different pages professing to explain this in "laymen's" terms but none of them address these two points. I don't believe in "tired light" as it is called but it may be part of the process in some way - photons do have mass as they are affected by gravity. As I understand it they have the same mass as an electron. If photons don't have mass then why are they affected by gravity - as in gravitational lensing?

    Ok, I have probably shown my complete ignorance here but I want very much to understand this whole process, so please be gentle and try to explain in language that a layman can understand.
    I will continue to check out reputable sites so if you can recommend any that use language that I can understand I would be eager to read them.
    I am not afraid of math but do not have education in anything higher than pre-trig... a handicap that I admit.

    Thank you,
    Paul
     
  2. jcsd
  3. Apr 9, 2010 #2

    Ich

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    Hi Paul, welcome to PF!

    You take the "expanding space" picture too literally. There is no medium that drags things along.
    "Expanding space" is a metaphor for the observed effect that the distances between galaxy clusters increase with time, with a velocity proportional to the distace. It has no physical meaning beyond that.
    So you're free to think of the clusters as simply moving away from each other, instead of imaginging "space" doing something to them.
    Balloon example does work perfecly accurate if you just imagine the poinst floating freely across the surface.

    No way. Redshift is quite different from light losing energy due to collisions. It's a shifting of spectral lines, not just light appearing redder.
    You already know that these models are called "tired light". There is a Wikipedia article with links (try Ned Wright's).
    No, gravity is not a force. It's spacetime curvature, it affects everything.
    It's not like the photon being pulled away from a straight line by a force, it's rather the "straight" line not being straight at all, like meridians on earth's surface: they are as straight as possible on a curved surface, but still they all intersect twice. The concept of a line as straight as possible is called a geodesic.
    No, they have zero rest mass, and arbitrary energy.
     
  4. Apr 9, 2010 #3

    bapowell

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    Paul, also note that your points address expansion in general, and are not specific to inflation.
     
  5. Apr 9, 2010 #4

    DevilsAvocado

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    I agree, but clearly Dark energy (in "space") is doing 'something' to the clusters... but then again, we don’t know what Dark energy is, so maybe it’s 'overkill' for a layman...
     
  6. Apr 9, 2010 #5

    Ich

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    You're right, but as bapowell noticed, the OP's points were not specific to it.
    If they mean inflation (or accelerated expansion), and not only expansion, things get more complicated.
     
  7. Apr 9, 2010 #6

    DevilsAvocado

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    Agree.
    "Brooklyn is not expanding!" :wink:

    The humorous quote from Woody Allen’s movie Annie Hall, says it all.

    Let’s pretend we figured out what Dark energy is, and that this energy pulls the galaxy clusters apart – this force is much weaker than the gravitation between Brooklyn and Earth and the Sun and the stars in Milky Way and our local galaxy group.

    There are theory’s that says that finally in an aeon, the 'pulling force' becomes dominant, and starts to dragging galaxies, solar systems, planets, Brooklyn, Woody Allen, and atoms apart – but this is just a theory, not verified.
     
  8. Apr 9, 2010 #7
    Ich,
    Thank you for the welcome.
    Expansion and inflation are different, how?
    I feel a bit obtuse here. How can these large mass ogjects (galaxy clusters) move at speeds exceding C? The answer given is that they aren't, space is expanding between them but in my mind it is the same thing. (d = t x v)
    If a point of mass is floating above the "ballon" what would accelerate it? (mass at rest remains at rest unless acted upon by an outside force) There has to be a connection between the space/time and matter unless the perception is explained by another function. (light bends as it goes through mediums of different densities?) I am trying to see this and why it has to be the standard answer of "dark matter".

    Do we know that dark matter/energy exists - other than through the expansion perception? (Is dark energy a cause or an effect?)

    OK, here is something that grabs me. "No, gravity is not a force. It's spacetime curvature, it affects everything." OK, I think I can accept that gravity is being defined as an effect rather than a cause. If space is expanding then the depression in space time is moving with these large masses and they move with the depression that their mass causes in space/time. I can make sense of that.

    Now I have to find a way to accept that space/time is expanding.
     
    Last edited: Apr 9, 2010
  9. Apr 9, 2010 #8

    DevilsAvocado

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    Rule #1: Absolutely nothing can exceed the speed of light, moving in space.
    Rule #2: Space itself has no speed limit.

    You must remember when talking about very distant galaxies, moving at extremely high velocities away from us – we are talking about our perspective.

    If there are any intelligent creatures on these distant galaxies, looking at our galaxy, we will be moving away at extremely high velocity – and they will be at rest.

    In fact, every observer in the universe will see any other observer moving away from him (except in the local group). And every observer in the universe will think he is at rest.

    Strange? Maybe, but think of the balloon that expand, hope you get the picture.

    https://www.youtube.com/watch?v=<object width="480" height="385"><param name="movie" value="http://www.youtube.com/v/I9Cjxd4Mjog&hl=en_US&fs=1&rel=0&color1=0x006699&color2=0x54abd6"></param><param [Broken] name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/I9Cjxd4Mjog&hl=en_US&fs=1&rel=0&color1=0x006699&color2=0x54abd6" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="480" height="385"></embed></object>

    Dark Matter and Dark Energy are two completely different phenomena. DM is attractive and DE is repulsive. Both have been observed more than once, and DM has support in current theories, but none is finally settled.

    The expansion of the universe is one of the most established facts in cosmology, both in theory and in physical proofs. The cosmic microwave background radiation (CMB) is everywhere to prove it.
     
    Last edited by a moderator: May 4, 2017
  10. Apr 9, 2010 #9

    bapowell

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    Be careful with this. DE has not been observed. What's been indirectly observed is the accelerated expansion of space. This very well could be dark energy, but it could also be f(R) gravity, or something else. It's important to make that distinction.
     
  11. Apr 9, 2010 #10
    Do you have any evidence for this? Ignoring dark energy for now, a Massive black hole at the centre of a galaxy *could* be dragging spacetime around it such that it becomes like a disk of spacetime where "dark matter" has a novel but reasonable explanation.

    Such descriptions of large scale phenomena could also explain dark energy; if the background has it's own substance, and a level of energy massive enough for a cup of it to boil all the oceans of earth (cf Feynman), it would surely follow the basic laws of thermodynamics where energy is active in moving to where it is not.

    We really need to rethink things from first principles, but the moderators here seem so sure they know near to everything that they ban you for life and call you a "crackpot" just for trying to bring physics to a place where fundamentals are important, not the latest band-aid holding up a wobbly structure.

    Only those who have invested interests in the status quo would ban the expression of ideas, the asking of questions.

    Hegel's dialectic may not be the full description of these things, but deleting ideas and burning books, when genuine unanswered questions were the subject, is evidence that progress is hindered by those who are afraid of the great and wonderful mysteries that confront us.
     
  12. Apr 9, 2010 #11

    bapowell

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    Plaster, I think you should spend more time working on your new theory of everything and less time making asinine, tired claims about the intentions of the good people in this forum.
     
  13. Apr 9, 2010 #12
    Einstein was concerned that specialisation would lead to a loss in terms of understanding the big picture. When did science change from the persuit of the unknown, to the ridecule of challenging ideas whilst accepting the rediculous idea that gravity is not a force.

    Of course this post will be deleted and I will be banned for life again as a "crackpot", I'm certainly no expert on anything.

    Where would science be now without generalists? Answer honestly before you delete me, please.
     
  14. Apr 9, 2010 #13
    I love the forum. But I do feel sad that I had to delete all the cookies on my iPhone just to be able to visit the site without a message about me being a "CRACKPOT" blocking me from reading anything here.

    I have no problem with people being offensive to me if I've offended their sense of what's reasonable. I love it when people give reasons as to why my ideas are wrong. I find it plain wrong when I'm banned for approaching things from a different direction.
     
  15. Apr 9, 2010 #14
    DevilsAvacado,
    I believe that there is enough evidence (from what I have learned here and what I have read) to suggest that space/time is expanding and I think I understand how the galaxies can be moved with it. Thank you and Ich for the help.

    OK, I had an idea that dark matter and dark energy would be different.
    So, is dark energy responsible for the expansion of space/time or is it an effect of that expansion?

    What other evidence do we have that dark energy exists?

    thank you for being kind enough to explain,
    Paul
     
  16. Apr 9, 2010 #15

    bapowell

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    We have evidence that in recent times the universe began to undergo accelerated expansion. There are several independent pieces of evidence: measuring the distance-redshift relation of distant supernovae shows that only a universe that has recently begun to undergo accelerated expansion fits the data well. Measurements of the cosmic microwave background, in particular, the integrated Sachs-Wolfe effect, show that large scale correlations are larger than they should be in ordinary, non-accelerated spacetime.

    Dark energy is a very unique kind of stress energy that causes accelerated expansion of spacetime. It is one explanation for the above pieces of evidence, however, it has not been measured directly and it is also not the only competing theory. However, careful analysis of the temperature fluctuations in the CMB and large scale structure data (like galaxy surveys) all point towards the fact that matter (ordinary and dark) makes up only around 30% of the energy density of the universe. The remaining 70%, when modeled as dark energy, give predictions that match incredibly well with observations.
     
  17. Apr 10, 2010 #16

    DevilsAvocado

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    Thanks bapowell, for an excellent explanation. I just want to supplement with this astonishing picture of the content of the universe:

    DarkMatterPie.jpg
    Conclusion – 96% of the universe is made of something that we do not clearly understand (yet)! :surprised
     
  18. Apr 10, 2010 #17

    DevilsAvocado

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    You’re absolutely right, sorry for being 'unclear'.

    Rephrase:
    There have been observations of 'phenomena' that are (for now) titled Dark Matter and Dark Energy, but this is completely different from e.g. the observation of the cosmic microwave background radiation (CMB), which we can observe directly and understand perfectly well in current theories.

    As for Dark Matter, the most famous 'indication' is the http://en.wikipedia.org/wiki/Bullet_cluster" [Broken]:

    bullet-cluster.jpg


    But there are also other observations pointing in the same direction, http://en.wikipedia.org/wiki/MACS_J0025.4-1222" [Broken]:

    http://www.spacetelescope.org/images/screen/heic0818a.jpg" [Broken]
     
    Last edited by a moderator: May 4, 2017
  19. Apr 10, 2010 #18
    So as of right now we don't know whether dark energy is a cause or an effect from some cause not yet understood?

    How likely is light itself being what is driving space time apart? It does have force - look at a radiometer. It would be a very weak force that would reach every part of space in all directions. It would not be strong enough to overcome the gravity of clusters of large mass in local communities. There is a lot of it around and it travels at C so the kinetic energy would be signifigant in the absence of signifigant gravitational forces.
    Like I said - I have no idea whether it is possible but gravity was invented as a cause for the curvature of matter when it is in fact an effect of the curvature of space / time.

    It seems too easy to just label what we perceive with a new name for something we don't yet understand.
    Thanks for the help,
    Paul
     
  20. Apr 11, 2010 #19

    bapowell

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    Not quite. Dark energy, when we put it into the equations of general relativity, gives a universe with an accelerating expansion. We also happen to observe accelerated expansion. It therefore offers one explanation. However, it's not the only way to get accelerated expansion (AE). We can modify the gravity theory itself. So, we have a convincing observation of AE, not of dark energy per se, since there are others possibilities.
     
  21. Apr 11, 2010 #20
    OK, Thank you for the education.
    I feel good about what I think I have learned and the limits of it.
    I am going to stick around and maybe learn more, if that is ok.
    Paul - the old guy who is still curious.
     
  22. Apr 23, 2010 #21
    Contrary to 'popular' belief, "SPACE" is not expanding! So, "How", you ask, "can the Universe expand if 'space' is not?" The answer is simple, so simple that most, if all, miss it. Since the Universe is 'everything', that is everything finite, everything else is 'nothing'. So here you have two entities: Everything, that is everything that IS, and you have Nothing, that is, everything ELSE! "Nothing" [a] cannot expand because if you remember your highschool math, "0" times any number remains "0". Plus, "Nothing" does NOT need to expand because it is ALREADY everywhere! Think about it: 'Something' takes up space; all else IS 'space'. Simple, right?
     
  23. Apr 23, 2010 #22
    You hit the nail on the head. Humans are very good at doing that. The best [I can think of at the moment] example of such a label is the word "Infinite". Actually, when you really stop to think about it, there is NO such 'thing' as Infinite. "Infinite" is just a word meaning: "I've reached the limit of my pathetic brain!" Remember in high school: "Parallel lines converge at infinity"? Think about that one. If two lines are truly parallel, they will NEVER convege, and IF they EVER do converge, they are/were not parallel to begin with, and there is no such place as "Infinity" except in our heads.
     
  24. Apr 23, 2010 #23

    bapowell

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    No, not simple. You are highly confused. We are discussing the empirical result that two points in space will move apart from each other over time. Space expands in the sense that our notion of distance increases with respect to time. I don't think your unfocused ramblings are contributing anything useful to this thread.
     
  25. Apr 25, 2010 #24
    I agree. And it's people like hugh that make it more difficult for reason to be at the centre of things. It's even difficult to find a context to argue against.
     
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