What is Expanding: Definition and 634 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. Feeble Wonk

    Field Lines in Expanding Space Explained

    Can anyone explain to an ignorant layperson, with as little mathematics/geometry as possible, whether field lines in expanding space become "farther apart". I view this question as being closely related to the concept of quantum foam distribution in expanding space... do virtual point particles...
  2. I

    Expanding function with spherical harmonics

    Homework Statement The function cos(theta)*cos(phi) in spherical coordinates cannot be expanded to a series of spherical harmonics. Explain why. Homework Equations As far as I can recall, the spherical harmonics are a complete set over a sphere, meaning every function which is SI over a...
  3. L

    Why does redshift indicate that space-time is expanding

    Since nobody answered my last question I''l try it this way: Why does redshift indicate that space-time is expanding and not that galaxy's are just flying away from each other?
  4. L

    Redshift: expanding space-time or galaxy moving away form each other?

    I know that Hubble observed redshift which led to the conclusion that space was expanding. But why did redshift lead to such conclusion? Why didn't they just think that galaxy were "flying" away from each other instead of thinking that it was the space that was actually expanding? What made...
  5. L

    Who was the first one to say universe is expanding?

    Who was the first one to come up with the idea that the universe is expanding, and also had a form of evidence for it? Was is Friedmann, Sitter, Hubble or Einstein himself? Or was it someone else?
  6. L

    What is the relevance in knowing that the universe for example is expanding?

    Why exactly is it so important to know about the models of the universe(flat/open/closed)? Why is it so important to know that the universe is expanding? What do we benefit from it? what is the relevance of it? Even if we know the "truth", what does it mean to "us"? I don't really mean these...
  7. soothsayer

    Expanding Integrand into Power Function

    Homework Statement The dilogarithm Li2(x) is a special function defined by the following integral Expand the integrand in a power series and integrate term by term, thereby deriving the power series expansion for Li2 about x=0 Homework Equations f(x)= f(0) + xf'(0) + (x2/2)f''(0) +...
  8. L

    Expanding and Simplifying Two Sets of Double Brackets (most likely really easy)

    Homework Statement Expand and Simplify 6(x-1)(x+2)-(1-x)(2+x) Homework Equations The answer in the book is 7x^2+7x-14 The Attempt at a Solution I've tried several ways, but all of them give the wrong answer. I'm not sure what to do with the negative in the middle. I know it...
  9. C

    Intro Quantum: Expanding infinite square well

    Homework Statement Griffiths Intro to Quantum, problem 2.38: A particle of mass m is in the ground state of the infinite square well. Suddenly the well expands to twice its original size: the right wall moving from a to 2a, leaving the wave function (momentarily) undisturbed. The energy of...
  10. Z

    Evidence that the Universe is Expanding?

    Hi all, First let me say that I'm not an astrophysicist but that I have some understanding of classical physics. So it has been said that the universe is expanding, but what evidence is there of this other than the fact that things seem to be drifting apart? Since much of the universe is...
  11. N

    Blue shift galaxies and the expanding universe

    We are told the universe is expanding because galaxies are red shifted and that it is a doppler effect. Do blue shifted galaxies contradict the idea of an expanding universe?
  12. B

    How Can Fourier Series be Used to Expand a Continuous Function of Period 2L?

    please help on this question Any continuous function of period 2L can be expanded as a Fourier series f(x)=a0/2+∑(from n=1 to∞) (ancos(n pi x/L)+bnsin(n pi x/L)) Using ∫(from -L to +L) sin(m pi x/L)sin(n pi x/L)dx=L kronecker delta m n Show that Bn=1/L∫(from -L to+L) sin(n pi...
  13. L

    Exploring the Mystery of an Expanding, Infinite Universe

    I'm reading a lot of stuff about the expanding universe, and also about it being infinte. So now I was wondering: How can the universe expand while it's infinte? (or am I asking something that nobody really know's the answer to?)
  14. V

    Exploring the Edge of the Big Bang: What is it Expanding Into?

    I come from an experimental backround with no astronomy so I am hoping this question makes sense! If the theory of the big bang is correct and space started off at a singularity and is now expanding, there must be an outer edge to this? If this is true then what is it expanding out into...
  15. C

    Expanding into Power Series (Complex)

    Homework Statement Expand e^{1/z}/\sin z in powers of z+1+i.Homework Equations Not sure, see below.The Attempt at a Solution I already know that \begin{align} \sin z & = \sum_{n=0}^\infty \frac{(-1)^{n}}{(2n+1)!}z^{2n+1} \end{align} And the other expansion for the exponential (but we just...
  16. A

    Photon Red Shift Energy losses in expanding universe theories

    The evidence points to an expanding universe, we tell this by looking at the redshift/distance relationship, objects further away are receding faster, with their redshift and distance at an almost linear relation. My question is, the photons emitted by those objects that we are just now...
  17. G

    Universe only appears to be expanding.

    Has anyone ever given serious thought that the universe only appears to be expanding because most, if not all, galaxies have a black hole in the center sucking the galaxy into it? If you have X amount of galaxies basically being sucked into the black hole at their centers would it not look like...
  18. T

    Expanding exponential fucntions

    Homework Statement Expand (1+e^(2x)), and (1+e^x)^2. Are they any different. I am confused please help Homework Equations The Attempt at a Solution
  19. M

    Expanding Universe or Expanding Space?

    The question in the title of this thread was triggered after reading a couple of papers that, while accepting the assumption of an expanding universe, seem to question whether space itself actually expands. These papers are: http://arxiv.org/abs/0707.0380" Reference: ‘The Expansion of...
  20. K

    Expanding Present Time Universe at Omega 0 = 1: Help Needed

    the present time of matter dominated universe for \Omega_{0}>1 is : t_{0}=H_{0}^{-1}\frac{\Omega_{0}} {2(\Omega_{0}-1)^{3/2}}[cos^{-1}(2\Omega_{0}^{-1}-1)-\frac{2}{\Omega_{0}}(\Omega_{0}-1)^{1/2}] how to expand this at\Omega_{o}=1??help me
  21. mrspeedybob

    The expanding universe and the conservation of energy

    The universe is expanding. We know this because light from distant stars is red shifted indicating that they are moving away from us. Here is the nugget that just occurred to me. Lower frequency light carries less energy so if all the light emanating from a star shifts further down in...
  22. R

    Question about accelerated expanding universe theory.

    Hey, After watching a show on TV about expanding universe and dark matter&energy, I wondered the following. In the program, it was mentioned that the universe is expanding at an accelerated rate. This was measured using spectroscopy, comparing Type 1A supernovaes at different distances. It...
  23. M

    Expanding Universe: Cooling Matter, Gravity & Isotropy

    in an expanding universe is all matter cooling? also, is has gravity become weaker over large distances? does isotrophy apply to the natural forces?
  24. B

    Light Speed & Expanding Galaxies: A Cosmological Mystery

    If galaxies aer expanding fast than the speed of light how are we able to see them. At the moment this expansion surpassed the speed of light shouldn't these galaxies dissappear or remain unchanged visually?
  25. W

    Exploring the Observed Flow of Galaxies in the Expanding Universe

    Anybody out there with info? What part of the expandable universe have the galaxys been observed to be flowing to a pecticular direction. Been looking for information site on topic. Thanks
  26. R

    Red shift of light and expanding universe - Your help needed.

    This relates to Doppler's effect. The phenomenon: It is quite simple and says that light emitted from a moving object will be redshifted when the object is moving away from us (earth) and blueshifted when the object is moving towards us (earth). I was thinking of this phenomenon and arrived...
  27. F

    Expanding universe and energy question

    Hey so I've started learning some cosmology and i have a question about the expanding universe. So i was told to picture a 3D graph with time on the vertical axis and space making a plane perpendicular to the vertical. I am using the metric where the diagonals are (1,-a,-a,-a) where a is a...
  28. U

    Is universe expanding or contracting?

    gravity pulls two galaxies. Andromeda and Milky Way are going to collide in few billion years. this seems to show that everything in the universe is moving close to each other i.e. contracting. but, since the universe was formed, it has been expanding due to dark energy. how do you explain this...
  29. G

    Expanding x^n-a^n without Binomial Theroem ?

    Homework Statement This is the given Theorem in my book, everything seems fine except that I cannot figure how they expanded (xn - an) Homework Equations The Binomial Theorem The Attempt at a Solution According to me (xn - an) = {[(x+a)-a]n - an} and expanding it would yield...
  30. Nick666

    The universe is expanding. Into what ?

    The universe is expanding. Into what ?
  31. marcus

    Seething expanding geometry-new LQG view of reality

    Seething expanding geometry--new LQG view of reality A view of reality emerging from current LQG research (like 1004.1780) is somewhat analogous to the "seething vacuum" of quantum field theory. But it is a "seething geometry" in which bits of area and volume constantly come into existence and...
  32. J

    Is the Universe Really Expanding?

    How did scientists discover that the universe is expanding? This theory doesn't make much sense to me. What could be pushing the planets and galaxies away from each other? I just started reading magazines about astronomy such as "Sky and Telescope" and have started reading my physics textbook...
  33. K

    Exploring the Possibility of an Expanding Universe Beyond Black Holes

    I was wondering if someone agrees: Is it possible that on the other side of the black hole is an expanding universe? It seems an iteresting idea to me: in our universe a star collapses onto itself with an explosion, creating a black hole and on the other side a big bang happens with matter...
  34. Z

    If the universe is expanding more rapidly now

    Then what is the acceleration rate currently, what has been the change and will be the change in acceleration, and most importantly... If it's still accelerating...wouldn't the universe's expansion have passed the speed of light? (unless it's approaching that limit) That's about it. Oh...
  35. F

    Collapsing and expanding shell theorem

    I've been philosophing about Newtons shell theorem, which tell us that inside a symmetrical sphere, gravity is zero if the sphere is hollow, and linearly declining while moving closer to the center if the sphere is massive and of constant density. Now, if the sphere was hollow it would...
  36. R

    Expanding Function f(x)= x^2+xcosx in Fourier Series

    [b]1. Homework Statement [/b expand the function in Fourier seriesf(x)= x^2+xcosx I divided the function in separate part and try to expand it in Fourier series separately i have started with x^2 a_{0}= \frac{1}{2\pi}\int_{-\infty}^{\infty}x^2dx=\frac{\pi^2}{3} a_{n}=...
  37. T

    Expanding and Substituting: Solving (1-3x)^{\frac{1}{3}}

    Homework Statement Expand (1-3x)^{\frac{1}{3}} in ascending power of x , up to the term x^3 . By using an appropriate substitution for x , show that \sqrt[3]3=\frac{33809}{19683} Homework Equations The Attempt at a Solution the expansion would be 1-x-x^2-(5/3)x^3 and the...
  38. E

    Red Shift & Time: Can Time Be Expanding Too?

    Hello! I'm brand new to the forum and have a question that has been nagging at me for some time. I've read a great number of articles regarding the red shift, as well as time being a dimension. I was wondering if anyone has addressed the possibility that time might also be subject to the red...
  39. A

    How can we know that the universe is expanding

    I don't know much about astrophysics and have never studied it. So, if I am wrong at any point, kindly correct me. It is said the whole space-time fabric itself is expanding after the big-bang. If this is so then why do we at all feel the recession of the heavens? I will try to elaborate my...
  40. L

    Taylor Expanding Two Equations: Analysis & Results

    I have two equations: \ddot{x}^\mu + \ddot{y}^\mu + \Gamma^\mu{}_{\nu \lambda} (x+y)(\dot{x}^\nu+\dot{y}^\nu)(\dot{x}^\lambda+\dot{y}^\lambda)=0 and \ddot{x}^\mu + \Gamma^\mu{}_{\nu\lambda}(x) \dot{x}^\nu \dot{x}^\lambda=0 apparently if i taylor expand the first equation to first order...
  41. J

    Traveling in an Expanding Universe

    For starters let me say that reading about and pondering cosmology is only a hobby, I have no formal education in this arena, although I am returning to school this spring to do just that. That being said, the following query may be foolish for some basic reasons I have missed, or not come upon...
  42. R

    Expanding taylor polynomial

    Homework Statement Derive a method for approximating f'''(x0) whose error term is of order h^{2} by expanding the function f in a fourth taylor polynomial about x0 and evaluating at x_{0} \pm h and x_{0} \pm 2h. Homework Equations The Attempt at a Solution I'm not sure where to...
  43. V

    How Does Plasticity Theory Apply to a Spherical Cavity in Mohr-Coulomb Material?

    this is a short abstract of problm i m working upon..so please help ..suggestions are kindheartedly welcome... a spherical cavity of radius R in a Mohr-Coulomb incompressible material. properties are defi ned by Young's modulus E, Poisson's ratio v, internal angle of friction (shi) i...
  44. T

    Expanding expectation equation; Linear algebra

    Kalman Filter - Covariance Matrix Kalman Filter Problem Homework Statement I have the following expectation formula: P_k=E\{\left[(x_k-\hat{x}^-_k)-K_k(H_k x_k+v_k-H_k \hat{x}^-_k)\right]\left[(x_k-\hat{x}^-_k)-K_k(H_k x_k+v_k-H_k \hat{x}^-_k)\right]\}2. The attempt at a solution I'm told...
  45. G

    Expanding brackets with fractions

    I have no problem expanding brackets with fractions generally, unless the fraction contains an unknown variable, such as in the following expression: m/4[6m - 8] + m/2[10m - 2] I know that the answer is: 12/2m2 - 3m ..but I have no idea how to get to that. Can anyone help?
  46. G

    Expanding Brackets: Find Out Where You Went Wrong

    Where did I go wrong with this? -2e(e + 3) + 4 (e + 2) My answer is - 2e - 6e + 8 According to my book it should be - e - 3e + 6
  47. FeDeX_LaTeX

    Is Anything Else Expanding Like the Universe?

    The universe is expanding (at what rate, anyway? I can't understand how we'd figure out a 'rate'), correct? But is there anything else IN the universe that is constantly expanding? i.e. I've heard of the balloon analogy, but is there anything ACTUALLY increasing, perhaps not at the same rate as...
  48. T

    Internal Energy of an Expanding Gas

    Homework Statement 2 moles of a monatomic ideal gas expands from state A to state B. PA = PB = 600 N/m2, VA = 3.0 m3 and VB = 9.0 m3. i. Calculate the work done by the gas as it expands. ii. Calculate the change in internal energy of the gas as it expands. iii. Calculate the heat added to or...
  49. G

    Expanding and simplifying brackets

    Could someone please expain where I went wrong with this? expand and simplify the following: 1/8(6x - 12y) + 1/2(3x + 2y) I expanded the brackets like this: 0.75x - 1.5y + 1.5x + y and simplified like this: 2.25x - 0.5y But the right answer is: 2.25x - 2.5y
  50. F

    Temperature vs Volume in an expanding gas

    Homework Statement The energy of a gas is given by: E = 3/2*NkT-aN2/V, where E, N, k, and a are held constant (or are just constants). Volume V1 with temperature T1 expands adiabatically into V2. Determine T2. Homework Equations All in part 1. The Attempt at a Solution I'm...
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