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Effort to get us all on the same page (balloon analogy)

  1. Aug 5, 2015 #526


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    Well i have learned a lot today about the cosmos today. I can actually read a lot of what you guys are saying and understand it thanks for all the help =) the balloon seems like a pretty good explanation.
  2. Aug 15, 2015 #527
    I have a question regarding space-time (space).

    I have read a large part of this thread and numerous others; both here and elsewhere. (Thank you everyone!).

    I will state my understanding/assumptions in layman’s terms first. I would appreciate if someone could check I have correctly understood to this point. I will post further understanding and direct questions after that. Thank you.


    Space is expanding everywhere from all points in all directions.

    The universe is bigger than we can see or detect.(think flashlight in endless black room; room goes on after visability stops)

    It can expand at faster than the speed of light (C); space is expanding not moving.

    The rate of expansion can and has changed since the big bang (BB). (Is the rate of expansion currently increasing?)

    Space was created at the BB.

    The universe may or may not be infinite: it depends on curvature and the size of curvature.

    The universe may be too big for us to detect the curvature (point on a sphere would appear flat)

    If curvature is positive enough the universe can meet back up and is finite (describes a sphere with universe on the line, Space is not inside the sphere but on the line)

    If the curvature is zero or too small the universe is flat and infinite

    There appears to be two main groups of answers as to what the fabric of space is:

    Description A – Nothing its Mathematics

    · Space is really just a Geometrical construct.

    · Space (3d) only exists as a function or description of the location of matter; Time is a function of describing a point of matter moving with respect to another point of matter.

    · Curvature of space by gravity; nothing else

    · It’s a mathematical model or a function; nothing real

    Description B - Something

    · The Higgs field

    · Gravitons (is this the same as Higgs boson; a piece of Higgs field?)

    · Probability/Potential energy field

    · Aether/ether

    · Other alternatives.

    It would appear that both answers can be correct depending on your philosophical disposition.

    My observations on fabric of space:

    I appreciate the answer (Description A) intellectually and although it is undoubtedly correct (by definition of the model) it is also unsatisfying on a deeper level as an explanation. The universe is clearly more than just a mathamatical model.

    Mathamatics is just patterns; our models replicate patterns from the real world in the maths world. Our maths world in this context is imaginary; even if it predicts what will happen in the real world.

    This thought and my growing realisation of the depth of models/mathematics in our understanding of the universe may lead me to consider the possibility of the universe simulation scenario a little more seriously than previous.

    Mathamatics models a pattern independent of the medium (in this context) and can be considered a description. The universe models patterns in the medium of the universe it is physical in that sense and exists. I don’t find semantics much help i.e. “what’s an idea or thought made of”.

    Philosophically (to me anyway) space should be made of something whether that is a medium or a field, it should be something; nothing existed before something so it's not nothing.
  3. Aug 15, 2015 #528


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    Gravitons do not exist in curved geometry especially if the geometry is dynamic. The definition of a "particle" is problematic in a realistic geometry. It is a mathematical idealization that depends on geometric simplification (e.g. FLAT SPACETIME).
    The Higgs field is of course a mathematical idealization.
    You might ask what is the Higgs field "made of".

    I suppose events, interactions, are real, relationships are real---one can measure them. One can measure the angles of a triangle. Compare areas, compare volumes etc.

    Geometry is one of the realest things in our experience. We experience whether the angles of a triangle add to 180 degrees, or more, or less.

    Much of the rest of physics---of what we observe, control, measure in physics---involves geometry in large part. A large part of physics is made of geometry. Think of electromagnetism, the relations of moving charge and changing magnetic field---in large part geometric.

    Much of the rest of physics (besides the bedrock reality of geometry) consists of imagined creations of the mind, useful idealizations.
  4. Aug 15, 2015 #529


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    the moment anyone says "fabric of space" they have been distracted by a metaphor and have lost contact with reality.
    what is "fabric"? what is "space"? why should "space" be created.

    There are distances and angles that are very real, there are measurable relationships.
    the idea of space as a substance comes out of popular mass-market books like Brian Greene stuff. Seductive metaphors mess up our minds so somebody can be on television and collect royalties.

    It's not necessarily true that BB was beginning of time evolution, there are alternatives. Google "LambdaCDM bounce" or look up papers by Edward Wilson-Ewing on arXiv.org---he is one of dozens of cosmologists working on testable bounce cosmology (no singularity, no need for a mythical "inflaton" field, simple Occam explanations)
    Space was created at the BB.

    ...groups of answers as to what the fabric of space is:...
    My observations on fabric of space:
    Philosophically (to me anyway) space should be made of something whether that is a medium or a field, it should be something; nothing existed before something so it's not nothing.


    What is a "photon" made of? I think photons occur at emission, absorption, scattering events.
    I don't think anyone has ever seen a photon absent some interaction.
    It is a mathematical codification of our expectations, one that works well in flat Minkowski space time

    If a photon does not need to be "made of" anything, why should geometry be "made of" something?

    One can be led astray by language, by WORDS----like the noun "space". By the mental habits of language--oh for sure! if it is a NOUN then it must be "made of" something. Look at all these other nouns like "dog" "cat" "apple pie"---they are all made of something! BTW Lucky I liked your post, it sounds intelligent and articulate. I see things in a different light, from a different perspective, however, so wanted to respond.
    Last edited: Aug 15, 2015
  5. Aug 15, 2015 #530

    Thank you very much for your reply.

    My actual style of thinking is more akin to "out loud" and can appear a bit jumbled to others (particularly online); so I try to organise my thoughts coherently before posting to enable others to follow.

    I have a million questions I would like to blurt out right now however in the spirit of the above statement I will contemplate your points and read/scan BB alternatives suggested before reposting. Possible BB alternatives are something I have considered also but wanted to state my understanding of the mainstream perspective first.

  6. Aug 16, 2015 #531


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    My thinking too. You mentioned "mainstream" So just now thinking out loud, I went to the central listing of conferences to see what topics are of interest to mainstream cosmologists these days. Here are a few I noticed. It's a special year (centennial of Einstein GR) so that affects the makeup of the conferences.

    The 8th International Conference on Gravitation and Cosmology (ICGC)
    December 14 - 18, 2015.

    http://icgc2015.in/index.php/invited-speakers [Broken] (Parampreet Singh)

    23-28 November 2015
    Warsaw, Poland
    Invited plenary speakers include:
    • Jan Ambjorn (University of Copenhagen)
    • Giovanni Amelino-Camelia (La Sapienza, Rome)
    • George Ellis (University of Cape Town)
    • Jerzy Kowalski-Glikman (University of Wrocław)
    • Yongge Ma (Beijing Normal University)
    • Ezra T. Newman (University of Pittsburgh)
    • Tomasz Pawłowski (Universidad Andres Bello, Santiago)
    • Roger Penrose (Oxford University)
    • Martin Reuter (Universitaet Mainz)
    • John Stachel (Boston University)
    • Thomas Thiemann* (University of Erlangen-Nürnberg)
    • Kip Thorne (California Institute of Technology, Pasadena)
    * TBC

    The Planck Scale II
    XXXV Max Born Symposium
    Wroclaw, Poland, 7 - 12 September 2015

    A few of the invited plenary speakers are:
    • Giovanni Amelino-Camelia (Rome)
    • Aurelien Barrau (Grenoble)
    • Martin Bojowald (Penn State)
    • Laurent Friedel (Perimeter Institute)
    • Kirill Krasnov (Nottingham)
    • Jerzy Lewandowski (Warsaw)
    • Krzysztof Meissner (Warsaw)
    • Daniele Oriti (Golm)
    • Thanu Padmanabhan (Pune)
    • Alejandro Perez (to be confirmed) (Marseille)
    • Roberto Percacci (Trieste)
    Gravity @ all scales
    Nottingham - 24 to 28 August 2015
    http://thomassotiriou.wix.com/gravityallscales2015#!speakers/c10mn (Eugenio Bianchi, also Saueressig, Sakellariadou, Mercati and others)

    Hot Topics in General Relativity and Gravitation
    August 9th – 15th, 2015, Quy Nhon, Vietnam

    http://www.cpt.univ-mrs.fr/~cosmo/HTGRG-2/index.php?page=speakers (Wilson-Ewing, Yongge Ma and others)

    Here is the full list at the University of Frankfurt site that keeps track of current and upcoming conferences
    Last edited by a moderator: May 7, 2017
  7. Aug 16, 2015 #532


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    Earlier this summer there was the fourteenth Marcel Grossmann meeting at Rome. One of the really big ones. Pope Francis gave the opening talk. Abhay Ashtekar was one of the plenary speakers. He also gave a half hour talk in one of the parallel sessions listed here (namely QG3). Typically over 1000 cosmology and relativity researchers attend the Marcel Grossmann. They hear the plenary speakers in the big hall together and they divide up into different parallel sessions according to their specialties.
    Rome 12 - 18 July, 2015

    Here are several of the parallel sessions:

    QG1 - Loop Quantum Gravity, Quantum Geometry, Spin Foams
    Thursday session. Chairperson: Jerzy Lewandowski

    QG1 - Loop Quantum Gravity, Quantum Geometry, Spin Foams
    Friday session. Chairperson: Jerzy Lewandowski

    QG3 - Loop quantum gravity: cosmology and black holes
    Chairperson: Jorge Pullin, Parampreet Singh
    Last edited: Aug 16, 2015
  8. Aug 16, 2015 #533
    I gained an insight into my own thinking from Marcus’s replies (#528,529) that I will share in the spirit of this thread; as others may also be making the same mistake.

    It is easy for the educated layperson (that’s people like me) to confuse what is confirmed in physics and what is still a theory and to conjoin or combine elements of various theories together (incorrectly) to form a view of the universe and assume this is the accepted view of science.

    This becomes more likely if the layperson pays attention (without significant discrimination) to the daily media, Internet and YouTube; has undertaken reading or research on the subject without making a considered differentiation in their own mind as to what is confirmed and what is still theory and between theories.
  9. Aug 16, 2015 #534

    I see and accept what you are saying regarding geometry and mathematics. I always have I just find it unsatisfying (to me) on a deeper intuitive level. It’s a paradox I’ll just have to live with.

    Although I do note the maths definition (in our discussion) is independent of the medium; as pointed out geometry does not need any medium for space to exist:

    “If a photon does not need to be "made of" anything, why should geometry be "made of" something?”

    That does not exclude the possibility of space being made of something; the deduction being the medium is irrelevant.

    As mentioned in #527 “It would appear that both answers can be correct depending on your philosophical disposition”.

    It could be we see two answers to one question when in fact it’s actually two questions.


    I haven’t followed up on the suggested reading yet but would like to contribute a thought about the BB at this point.

    Just to be clear so some don’t make the wrong conclusion and think I’m mad. The following are thought exercises as to other possible explanations for the BB and Universe. I don’t believe them just entertaining alternative thoughts.

    Description A

    The currently accepted view of the BB (continuation of my understanding)

    Nothing existed before the BB

    All energy & matter, (including dark matter and dark energy) and space-time were created at the BB: this is the universe.

    It expanded from a singularity; that is it came into existence everywhere (reference frame inside singularity) and expanded from there.

    Description B

    Space-time existed before the BB.

    The BB by this definition then is: when all energy and matter (including dark matter and dark energy) are added to (inserted into) space-time.

    Any expansion is a result of the interaction with energy and matter and the rest or pre-existing state of space-time (thinking bounce rebound stretch or splash ripple).

    The universe may or may not be infinite in this description.

    Description C

    Space-time did not exist before the BB but something else did.

    Something in this description can be thought of as a very big container or field.

    All energy & matter, (including dark matter and dark energy) and space-time were added at the BB: this is the universe.

    Space-time is made of some medium {separate from energy and matter or at least in a different state}.

    In this example space-time expansion could be explained in two ways:

    1. Space-time is being “warmed up” so is expanding or;

    2. More space-time is being added to the system; (think adding more liquid to a virtually limitless container).

    The universe is finite in this example.

    I will go off and have a look at the suggested reading material to see what real scientists are thinking. Cheers.
    Last edited: Aug 16, 2015
  10. Aug 17, 2015 #535


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    I like your perspective, it is in some ways akin to my own. I suspect you could find "real scientists" (in the general sense of professionals who attend conferences, publish, give talks :^) all over the map described by your A, B, and C. And the "real scientists" can be partly or maybe even entirely wrong, we can't know the future of research, fundamentally new ideas can show up, new directions can be taken. But I still like to check out what is being talked about at the major conferences.

    The two biggest international conferences about General Relativity/Gravity/Spacetime etc are TRIENNIAL. They are the GR series and the MG series.
    The last GR was GR20 in 2013, attended by 844 participants
    http://gr20-amaldi10.edu.pl/index.php?id=1 [Broken]
    http://gr20-amaldi10.edu.pl/index.php?id=29 [Broken]
    So the next GR conference will be GR21 in 2016. It will be interesting to see who the invited plenary speakers will be, what the topics will be, who will chair the various parallel sessions. There should be announcements and a website soon, if not already.

    The last MG was MG14, just this year, attended by 1220 participants, so the next will not be until 2018. But we can glance at the speaker lists, parallel session topics etc. and maybe learn something.
    The MG organizers do tend to pick attractive locations: MG11, 12, and 13 were held in Berlin, Paris, and Stockholm. The MG14 website has links to the websites of past conferences if you want to check those out.

    The rationale for at least not completely ignoring these bigtime international conferences is, I think, that the organizers are smart people and they want their conference to be a success, so they invite speakers who reflect the current interests of the community---they arrange for talks about research that the community of people who attend conferences want to hear about and they pick chairpersons for the parallel sessions who want their parallel sessions to be successful and attract a lot of participants so these in turn reflect the live interests and hot research topics in the particular specialized areas, to some extent.

    One can be skeptical too. I'm a bit suspicious of the MG series because it is so glamorous. The plenary speakers tend to be famous---perhaps deservedly so, but...maybe too much focus on reputation/celebrity---and the venues have glitz.

    I wonder where GR21 will be held. It's next year. Do they have a website yet? New York!
    So says http://www.isgrg.org/activities.php
    And there is a preliminary web page:
    It will be held on the Columbia University campus, July 10-15 2016.
    Last edited by a moderator: May 7, 2017
  11. Aug 17, 2015 #536


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    I didn't mean to burden you with a lot of "suggested reading material", Lucky. All this conference material is just a window on "mainstream". One opportunity to get an impression of it.

    I only meant to suggest ONE ARTICLE as something you might read. I had a particular reason for suggesting it. Let me try to recall. It was what you get when you google "LambdaCDM bounce".
    It was by two postdocs: Yi-Fu Cai and Edward Wilson-Ewing.
    I suggested it back in post #529

    They provide a scenario that is as plausible as any, I think, for the start of expansion. Nothing as exotic as inflation. No "something from nothing" no original "quantum fluctuation" no "singularity". No "breakdown of the laws of physics". No "beginning of time".

    And they check that it is consistent with observations so far, at least in a preliminary way. they just came out with it around end of 2014, more work is needed. The takeaway message is that some of the more drastic and exotic stuff is not necessary to accept.

    Their scenario does not have to be TRUE. IT MERELY MEANS YOU DON'T HAVE TO ACCEPT ALL THE hype and propaganda about inflation and "the singularity" and breakdown of the laws of physics. There are other ways to explain the flatness and sameness-in-all-directions that inflation was invented to explain back around 1980. And to fit CMB data.

    Cai and W-E paper is not unique. There are plenty of people working on bounce cosmologies, and on alternatives to inflation. There are also bounce cosmologies that involve inflation., the two aren't mutually exclusive. And there are non-bounce cosmologies that also don't need inflation, but still have time going back before start of expansion without hitting a singularity. All kinds of variations. I just think Cai and Wilson-Ewing's paper is a particularly clear, short, unexotic, example. It is based on the standard cosmic model (cosmological constant Lambda, cold dark matter) and they are very interested in connecting with various kinds of observations

    Reading the non-technical understandable parts of one 14 page paper is, I think, an easy way to gain a measure of immunity to a lot of unconsidered (and probably unnecessary) assumptions people make about the start of expansion.
    BTW here is Ed W-E list of papers on arXiv.org
    You can see he has written some follow-up to the December 2014 one with Yi-Fu Cai.
    I'll get his author's profile
    It needs updating. He is now at the Albert Einstein Institute at Gölm, outside of Berlin.
    PhD 2011 advisor Abhay Ashtekar.
    Last edited: Aug 17, 2015
  12. Aug 19, 2015 #537
    It was meant a bit tongue in cheek and a bit as protection. Some sites whilst claiming to share knowledge are non-inclusive to those not deemed worthy. I can see that does not apply here now.

    As mentioned above I do need to get clear in my mind what QM, String (various) and GR theories etc. state and not to confuse.

    A philosophical thought as I think philosophy and physics have a lot in common.

    The universe follows patterns; both on a grand scale and a quantum scale and all scales between.

    I am surprised by the similarities between the universe and the brain; particularly in some images of the universe showing dark matter (or was it dark energy?) between galaxies and images of galaxies in different EMR wavelengths. Other images look like what might be seen through microscope. (Edit. I know the images are not photos but a representation of data collected)

    No I don’t think the universe is part of some gigantic brain just an example of similar patterns. Perhaps contemplation of patterns elsewhere in nature may lead to insight at another level.

    However we are part of the universe.

    As part of the system can you ever know the whole: by definition I would suggest no. {Open to debate but in absolutes its no. If we think we understand the universe then perhaps it’s part of a bigger multiverse}.

    The very fact we can imagine the universe from an external reference frame (as Max Tegmark attempts with maths and others as thought) may be a clue our universe is part of something bigger. Man after all has proven time and time again: if we can imagine it we can make it happen; or in science we prove it.
    Last edited: Aug 19, 2015
  13. Aug 19, 2015 #538
    An amusing thought on the universe brain analogy: are we part of the brain or a parasite?
  14. May 29, 2016 #539
    Whenever I have trouble understanding a concept, the balloon analogy always clears things up for me (so far). I am a visually oriented person. I just have to remember that the real universe has one more dimension than the balloon. However, perhaps some people may have a more difficult time with visual examples like the balloon. One poster above complained about galaxies being stuck to the surface of a balloon. When I imagine the balloon I don't have that issue so I need to remember that some people are stronger in areas other than visualizing. They use methods which I find difficult to imagine. Therefore it would be great for us 'visuals' to use it but not so great for others. Perhaps instead of fighting about how we understand things we can learn to share. So I would prefer not to subscribe to a gospel because it alienates people whose ideas might otherwise complement mine. As long as I can keep an open mind, that is.
  15. May 29, 2016 #540
    Whoops, again forgot to check the date... oh well, it's still a good post.
  16. May 30, 2016 #541
    Perhaps this point is obvious to all, but at the time the CMB was released, I suppose every point in space sent photons in every direction. What we observe now are just the photons that happened to be headed in our direction from every point (on a sphere) that has a (current) radius of 41 B LY. That is obviously much less than all of the CMB photons. Are there any numbers to go with either our local rate of arriving photons or the total number of photons that were released?
  17. May 31, 2016 #542
    Please ignore what I said about counting photons. Not well thought out.
  18. Jan 8, 2017 #543
    If we can't say space is expanding because it doesn't constitute a real expansion of any "stuff", then couldnt we conversely point at the "stuff" for what is occurring and say that relatively, matter is compressing?
  19. Jan 8, 2017 #544


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    The way in which the redshifts of different objects at great distances vary, makes it impossible to explain with "shrinking" or "compressing" matter. In other words, irrespective of how you "shrink the ants" on the balloon, it cannot explain observations.
  20. Jan 8, 2017 #545
    Thank you, but its now confusing for me that the terms aren't interchangeable whether you think of the model running and see the ballon expand or imagine the model while preserving a certain balloon size?
  21. Jan 8, 2017 #546


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    I referred to a fixed balloon size and a shrinking ant size - it cannot fit Hubble's law.

    There is however still a possibility that dark energy density is not completely homogeneous. Cosmologist David Wiltshire is a proponent of this idea. Check
    Wager between DL Wiltshire and T Padmanabhan.
  22. Jan 8, 2017 #547
    from the material there:
    "The mystery of dark energy is explained purely in Einstein's theory, through a deeper understanding of those parts of general relativity, which Einstein himself recognised as being difficult: the understanding of gravitational energy, given that space itself is dynamical and may contain energy and momentum."
    - David Wiltshire

    (which makes me wonder about dark energy and how much energy space contains in terms we already know about like photons, and what about sound even, but this is by the way)

    So mechanically compression is outside the accepted model and Hubble observations, I see, thankyou.

    I suppose I was asking in terms of both the actual mechanics and also in terms of becoming familiar with the analogy.

    I see the problem of gravity leaves a gap for much speculative investigation that I wouldn't lately want to get into.
  23. Jan 10, 2017 #548


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    The first step in closing that gap is to acquire an understanding of general relativity, so that you will at least know what is already known.
  24. Jan 11, 2017 #549


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    This thread has been open for many hundreds of posts, and it's becoming increasingly difficult to keep it organized and useful so we are closing it.

    Followup questions should go in new threads, and as always if you want to add something specifically to this thread, ask a mentor and we can reopen as needed.
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