What is Expanding: Definition and 635 Discussions

The expanding Earth or growing Earth hypothesis asserts that the position and relative movement of continents is at least partially due to the volume of Earth increasing. Conversely, geophysical global cooling was the hypothesis that various features could be explained by Earth contracting.
Although it was suggested historically, since the recognition of plate tectonics in the 1970s, scientific consensus has rejected any significant expansion or contraction of Earth.

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  1. J

    Unraveling the Mystery of Spin Connection in an Expanding Universe

    Hello, I've worked through most of Carroll's appendix on the non-coordinate basis. I see and agree how the spin connection and tetrad one-forms are useful while calculating. However as an example he sets out to apply the formalism to a spatially flat, expanding universe. ds^2 = -dt^2...
  2. robdelory

    Expanding Universe Slowing Down and Then Speeding Up

    Hubble observed that not only is the universe expanding but that it is accelerating. With the model of the Big Bang as I understand it, the universe began as a big explosion. That would mean that it expanded at a rate exceeding the speed of light or at least close to it. If that is correct, that...
  3. H

    Why isn't everything expanding in an expanding universe?

    Viewpoint 1: Because gravity or other forces that are holding the thing concerned (be it a galaxy, a ruler or an atom) together are way stronger than the "force" caused by the expansion of space. So strictly speaking, space does in fact expand everywhere, including the space inside an atom...
  4. slatts

    Is "heavy nothing" already infinite or is it expanding?

    I need some help from people who can read the math in papers by such physicists as Linde. In his 2014 paper (on the web) "Inflationary Cosmology after Planck 2013", he says, "False vacuum is a metastable state without any fields or particles but with large energy density. Imagine a universe...
  5. SU403RUNFAST

    Taylor expanding a physics formula

    < Mentor Note -- thread moved to HH from the technical math forums, so no HH Template is shown > So the original problem was that a stationary hydrogen atom changed states from excited to lower state and emitted a photon, i solved for the energy of the photon hf taking into account the kinetic...
  6. Quarlep

    How much energy do we need to make an expanding universe?

    I know that universe can be have three different futures.But for lastes theories universe is growing faster then we thought.I want to ask how much energy we need to make this observable universe.
  7. K

    Calculating force applied from an expanding disk

    Hello, I need to calculate the force applied within a clutch pack by an expanding disk. Can you guys tell me if there is anyway to do this? I am working to find the torque capacity of a centrifugal clutch using the equation: Torque Capacity = 2/3 * COF * n * F * Radius Gyration where COF =...
  8. S

    Our universe as an expanding sponge that is constantly falling.

    Guys I know this is absurd, but it kinda makes sense to me. Recently, while i was doing housekeeping, I asked my brother to throw a piece of sponge down. He compressed the sponge and dropped it down. While the compressed sponge was falling, I saw it expanding. Seeing this, I realized that the...
  9. tressure

    Is the universe truly expanding?

    Hello everyone, i am just bothered by the theory that our universe is expanding, if so i want to know, what substance is filling the void as our universe expands, and where does this substance come from, Thank you
  10. Meron

    What's the nothingness that our universe is expanding into?

    We all know that the universe is expanding. What I'm curious about is what it is expanding into.
  11. akashpandey

    Why is the universe expanding if its temperature is cooling?

    If temperature of universe is cooling then why universe is expanding.
  12. wolram

    What is the evidence for an accelerated expanding universe

    Is the red shift evidence enough to define accelerated expansion
  13. Qturtle

    Expanding the Hamiltonian around a point of symmetry

    Hey I have a tight binding Hamiltonian of a BCC lattice which is a 4x4 matrix in k space (the 4 elements correspond to 4 atoms that are in a unit cell) I want to expand it for small k's around the symmetry points P or Gamma or H. I'm looking at a paper by J. L. Ma˜nes, PHYSICAL REVIEW B 85...
  14. E

    Uncurving the Universe: Expansion After Big Bang & Energy Loss

    Is the expansion of the universe after the big bang just the the "uncurving" of space time from an inconceivable point? And if so, is the loss of energy that curved it that much the only thing that could allow it to "uncurve"? I hate to use the word loss of energy, but I'm not for sure where...
  15. V

    Expanding gravitational systems

    Suppose that everything in the Universe - the radius of the sun, the astronomical units, radius of atoms, and everything else were to expand proportionately during the same period of time. This would mean also that the ratio of the time period of the various planets around the sun, and all local...
  16. Tadhgrrr

    Thermal expansion: the amount of material expanding is "irrelevant"?

    Hello everyone! First time asking a question here, go easy on me! I am a first year Mech-Eng student in Ireland, and I need some guidance from one of the amazing brains here at physicsforums. I am told by my thermofluids lecturer that in thermal expansion, the amount of material expanding is...
  17. M

    Calculating Work Done by Expanding Gas in an Automobile Engine

    Homework Statement In a cylinder of an automobile engine, immediately after combustion the gas is confined to a volume of 50.0 cm3 and has an initial pressure of 3.00x106 Pa. The piston moves outward to a final volume of 300 cm3, and the gas expands without energy transfer by heat. (a) What...
  18. E

    Why did dark energy overcome dark matter to create the expanding Universe?

    Why did dark energy overcome dark matter to create the expanding universe we live in today?
  19. I

    Universe Expansion: Why Objects Move Away Faster The Farther We Look

    Please forgive my lack of knowledge about the more complex ways that we have determined that the rate at which the universe is expanding is increasing, but one thing puzzles me. I have read that based on measurements of the red shift of light we have concluded that the farther we look out into...
  20. B

    Can Quantum Mechanics Explain the Expansion and Contraction of Space-Time?

    People often use the expanding balloon with galaxies on the surface to represent the expansion of space. But this view doesn't show how this expansion works in 3d and it doesn't show how gravity comes into play. Instead of putting the galaxies on the surface of the balloon all we have to do is...
  21. ELB27

    Evaluating an integral for an expanding, charged sphere

    Homework Statement An expanding sphere, radius ##R(t) = vt## (##t>0##, constant ##v##) carries a charge ##Q##, uniformly distributed over its volume. Evaluate the integral Q_{eff} = \int \rho(\vec{r},t_r) d\tau with respect to the center. (##t_r## is the retarded time and ##d\tau## is an...
  22. S

    Making sense of distance and speed of expanding universe

    I'm trying to reconcile the fact that regions of the universe are expanding faster than light, and that as a consequence the observable universe is far more than 13.7 billion light years across. I trust these are the facts, but I'm stuck figuring out how we know these to be true. I feel like...
  23. polygamma

    Convergence of Taylor Series and Definite Integrals: Exploring the Relationship

    Homework Statement If \int_{0}^{1} f(x) g(x) \ dx converges, and assuming g(x) can be expanded in a Taylor series at x=0 that converges to g(x) for |x| < 1 (and perhaps for x= -1 as well), will it always be true that \int_{0}^{1} f(x) g(x) \ dx = \int_{0}^{1} f(x) \sum_{n=0}^{\infty}...
  24. J

    Expanding Universe: Is Kinetic Energy Behind Acceleration?

    Could the accelerating rate of the expansion of the universe be due to the conversion of potential energy to kinetic energy? At the early stages of the big bang there would be tremendous amounts of potential energy (because it was so compressed). As it expanded, the universe, by the conservation...
  25. S

    Question about Space -- Is Space itself a 4th dimensional object?

    Ok, so I was just in physics class today and we were talking about special relativity... anyways, the instructor referred to how the universe is expanding, and so much so that there are places we could never ever get to because it's expanding fasterling than the speed of light. Anyways, this...
  26. B

    Uncovering the Mystery: 2D Creatures on Expanding Sphere

    Some 2D creatures are living on a sphere that it radius in increasing over time. They think that they are living on a expanding plane. The max speed of information is speed of light. The life time of the creatures are very smaller that the radius divided by speed of light. How can they find out...
  27. Paul Howard A

    Expanding universe and thermodynamics

    As I understand it, space continues to expand everywhere. But bound systems such as atoms and solar systems stay the same size due to local interactions. If this be true, should not energy be continually released by this "falling in" of matter within every atom, molecule, and planetary system...
  28. S

    Expanding a multivariable function in powers of one of the variables?

    So I've started reading Landau's classical mechanics text and I'm at the part where L(v'2) = L(v2 + 2v⋅ε +ε2) and he says to expand it out in powers of ε to get L(v'2) = L(v2) + ∂L/∂(v2) * 2v⋅ε where v and ε are vectors. Can someone explain how this result is obtained in more detail?
  29. A

    Could the Event Horizon of black holes be the edge of expanding universes?

    I recently read a few articles that contradict Einstein's Singularity theorem. The idea being that black holes are wormholes to other universes; with a white hole on the other side of the black hole (Poplawski's theory). What if instead of being a portal to another universe, the Event Horizon of...
  30. G

    Expanding Universe: Verifying Space Expansion Through Galaxies

    How one can say that the space is expanding by just verifying that the galaxies are speeding away from each other?
  31. HZY

    Why can the universe be expanding inward away from point of singularity (POS)?

    Much has been said about the universe expanding from a point of singularity (POS). But why can't the POS be a shell of singularity (SOS) such that the expansion would take place inside the SOS without breaking it. Did anybody thought about that?
  32. W

    Expanding universe - some thoughts

    I had some interesting ideas concerning the mechanics behind the space expansion and its acceleration. Here they are. I know you expect blunders, but I hope you will find something interesting. Starting with obvious:1. In the presence of strong gravitational field, time flows slower than in its...
  33. T

    Why do only even values of n show up in the expansion of sin4x?

    Homework Statement Hello, I found this problem in the book I borrowed from the library, but this book does not have solutions in the back...I tried to lent the solution book but the library does not have it...so could someone help me out? The question is: It is possible to decompose the...
  34. R

    Sinking instead of expanding universe?

    We all know the concept of the universe expanding. Would it be possible that the universe is not expanding at all, but the spacetime between objects is increasing? My question comes from the idea that spacetime is changed due to the presence of gravitational objects and the idea that gravity is...
  35. snoopies622

    Expanding Cube Roots: Solving Limits with Maclaurin Series

    A quiz at the end of Steven Krantz's Calculus Demystified includes the following problem: Find \lim_{x \to \infty} [ \sqrt[3]{x+1} - \sqrt[3]{x} ] I see how one can use the Maclaurin series to get \sqrt[3]{x+1} = 1 + \frac {x}{3} - \frac {x^2}{9} + \frac {5 x^3}{81} + . . . but trying it...
  36. S

    Is the Universe Actually Collapsing Instead of Expanding?

    Greetings everyone! I used to be a huge big bang theory fan, but these days it strikes me as the most eloquent example of scientific conformism. I can fully understand that the only real alternative to it can be nothing else but a Big Nescio Theory, though ignorance can be very creative when one...
  37. T

    How does the expanding universe affect matter/energy

    Rephrase from another thread I posted a while back; If you believe as masses increase in distance gravitational potential increases relative to the distance (the greater the distance the greater the gravitational potential). So as matter increases in distance from each other due to...
  38. M

    Could the Universe Be Expanding as Wave Fronts?

    Could the universe be expanding wave fronts and the fundamental particles of matter be the particle manifestation of the waves? The wave front surface being the 3 dimensions of space and the radius of the front being the time dimension - similar to a wave front of light but one extra dimension...
  39. A

    Universe is expanding like a balloon

    I've seen the example when people say the universe is expanding like the surface of a balloon. You have dots on that balloon which are galaxies and as you blow up that balloon they grow further away from each other. If the universe is expanding equally isn't there a centre which is constantly...
  40. A

    Expanding space thru matter vs matter thru space

    So the universe is expanding, rather space is expanding. By expanding we mean space is coming into existence at all points. Is that an equal rate of expansion everywhere? Now the expansion does not over come the force holding matter together, planetary systems, galaxies even galactic...
  41. karush

    MHB Find the volume by revolving around the x-axis without expanding

    A solid is generated when the region in the first quadrant enclosed by the graph of , y=(x^2+1)^2 The line x=1 , the x-axis, and the y-axis is revolved about the x-axis. Find the volumn $$ V=\int_{a}^{b}\pi\left[f(x)\right]^2 dx =\int_{0}^{1}\pi\left[\left(x^2+1\right)^2\right]^2 \,dx...
  42. D

    Expanding universe, big bang question

    I've always been curious about about the big bang because (from what I've read) it's a point we're not able predict before. Is there a possibility that our view of an expanding universe just means we can't see beyond the big bang? Or is there a reason that is ruled out and that everything...
  43. S

    Can the universe be both infinite AND expanding

    I was researching the inflationary model of the universe and came across the idea that the universe may be both infinite and expanding; and that there isn't a contradiction. As time goes by, the amount of matter in any given area will become less dense due to the metric expansion of space...
  44. M

    Exploring the Mystery of Expanding Galaxy Rates

    We know that distant galaxies (which are expanding) are sometimes expanding at rates that do not conform with our known theories and formulas developed by our own observations of gravity. Einstein's theory is of course at the forefront of this conundrum. To explain it some believe that we...
  45. Y

    Energy of an Expanding Universe Decreases?

    The energy 'U' of a uniform spherical volume (e.g., a Hubble sphere) is (3/5)(M^2)G/R Conventional wisdom has it that G and M are constant - at least in the preferred models that we are permitted to discuss on these forums. So when the Hubble sphere expands, we really don't expect a loss of...
  46. G

    Are We Also Expanding with the Universe?

    Universe is expanding. I know that all the galaxies are getting away from each other due to the expansion. So in theory is it true that we along with every other system of particles are getting stretched with the space ( or the distance between our constituent particle is getting bigger and...
  47. ChrisVer

    Scalar field in Expanding Universe EOM

    I would like to ask something. How is the solution of EOM for the action (for FRW metric): S= \int d^{4}x \sqrt{-g} [ (\partial _{\mu} \phi)^{2} - V(\phi) ] give solution of: \ddot{\phi} + 3H \dot{\phi} + V'(\phi) =0 I don't in fact understand how the 2nd term appears... it...
  48. Z

    Why the Universe is accelerating as it is expanding

    Hello all, thank you for taking the time to read this post, i appologise if it is in the wrong section, as i am new to this. Why did people just invent Dark Energy to explain the accelerating expansion of the universe? I propose another idea that doesn't rely on fudging numbers to explain...
  49. Y

    What do we exactly mean by space is expanding?

    I know this question had often been asked on PF but I don't get them. What do mean when we say that space is expanding? I mean that space is no physical entity that can expand. Space is just (apparently) "nothingness". Please solve my confusion.
  50. L

    If the universe is expanding, how can 2 galaxies collide?

    Sorry if this has been answered before, I am very new to this forum. So, if the universe is expanding, how is it possible that Andromeda galaxy, and our Milky Way will collide? Should they not be moving away from each other, given that the distance between them is big enough for space...
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