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. nukeman

    Really basic expanding question: Forgot how

    Homework Statement Going through my review material, and I need some help on this simple procedure. example 1: (2x + 1)^2 example 2: 2(x^2 -1) I forgot how to do this. Can someone please help me out? Homework Equations The Attempt at a Solution Example 1: 2x squared...
  2. Y

    Creation annihilation operators - expanding brackets

    I would like to normal order the following product of creation-annihilation operators, set up in Maple 16 as follows. The problem is, Maple won't perform "expand" (lowercase e) on the last step below (evaluating sigma3(x) :=[op1+op2]*[op3+op4]*[op5+op6] ); , which makes setting up the entire...
  3. dedwarmo

    The Universe shouldn't look like it does if it is expanding

    If the Big Bang is true then 14.7 billion years ago the universe was the size of a pea. We are seeing the most distant objects as they were 14 billion years ago. Shouldn't the most distant objects appear to be closer together than objects near us? Shouldn't the universe be denser the further...
  4. Q

    Will the expanding universe really end up cold and empty?

    If you take it to its extremes and space continues to expand at an accelerated rate, what happens when? 1) space is expanding so fast that virtual particles cannot annihilate. 2) if the space between quarks ends up expanding then the energy needed to pull them apart will spawn new quarks...
  5. H

    Expanding universe into what?

    Dear all, I just read a great question on TED.com, however I think people over here could answer this question perhaps better. "If the universe is expanding - what is it expanding into? what is THAT space called and why isn't it part of the universe now?"
  6. G

    The Universe is expanding, but why aren't we?

    Theoretically, the universe is expanding uniformly over time, dragging the galaxies along with it, right? That's why we can see the galaxies flying away from each other faster than the speed of light. But I was told they are not technically moving through space but with it. Like drawings on the...
  7. G

    Why galaxies are not expanding

    I'm pretty sure this answer is not known but it always good to double check. Dark energy causes space to expand but the space inside a galaxy does not. Does anyone know why? I'm pretty sure the answer is not known, so I have a guess as to why this might be the case. Particles send out...
  8. Ikon Rahu

    Is the Expanding Universe Affecting Our Solar System?

    I am curious about the expanding universe - that is, that the space itself is expanding. Why can't we notice the effects of an expanding universe here in our own solar system? Why doesn't space expand here around us? Wouldn't this result in more space between our molecules and so on until we...
  9. R

    How do you calculate BTU of expanding compressed air

    I would like to know if there is a measure, in BTU's, of the cooling effect from the release of compressed air through a nozzle and how it relates to PSI
  10. P

    Critical density in our expanding universe

    I am only a beginner in physics and have been reading popular books. I read that the average mass-energy density of the universe determines its shape such as having uniform positive curvature, uniform negative curvature, or zero curvature if it equals the critical density. However, if spacetime...
  11. StevieTNZ

    Expanding over R and L polarisations

    We expand over, in the H/V basis, |RR> + |LL>, likewise |RR> - |LL>. Because R = (H + iV) and L = (H - iV), how do we factor in the complex number to obtain the final result? So: 1. (H + iV)(H + iV) + (H - iV)(H - iV) and 2. (H + iV)(H + iV) - (H - iV)(H - iV) Thanks, Stevie
  12. andrewkirk

    Why is the Hubble sphere expanding?

    Hubble’s law, according to Wikipedia, says that the recession velocity of a distant object P comoving with Earth is vrec=HD where H is Hubble’s constant and D is the proper distance from Earth to P. The Hubble sphere is the area of space in which all objects comoving with Earth have vrec less...
  13. E

    Expanding Spacetime - Inside an Atom?

    I think that it is correct to say that everywhere, spacetime is expanding. Is it expanding within the radius of electrons within atoms? Are the radii getting larger over time? I believe it correct that the distance from the nucleus to an electron exceeds the diameter of either one by...
  14. B

    Expanding gases leaving a muzzle

    Homework Statement The expanding gases that leave the muzzle of a rifle also contribute to the recoil. A .30 caliber bullet has mass 0.0072kg and a speed 0f 601 m/s relative to the muzzle when fired from a rifle that has mass 2.8 kg. The loosely held rifle recoils at a speed of 1.85 m/s...
  15. D

    Expanding Gamma function around poles

    Can someone help me to expand the following gamma functions around the pole ε, at fisrt order in ε \Gamma[(1/2) \pm (ε/2)] where ε= d-4
  16. C

    Need Help Understanding Expanding Universe

    Hello, I am hoping someone can help me to understand that the universe is expanding and other questions that brings up. If it is expanding, does that mean that there is an edge or a place that the universe has not reached yet but will reach at some point? What would be in the space that it...
  17. D

    Expanding Logarithms with Radicals

    Homework Statement log2√xHomework Equations The Attempt at a Solution I thought that it might be something like log2x - log2x but that's not right. The book examples don't have any radicals.
  18. L

    Integral - an alternative to expanding the denominator?

    Integral -- an alternative to expanding the denominator? The following integral can be easily solved by expanding the denominator but I am wondering if there is a another way to solve it \int\frac{1}{(x+1)^7-x^7-1}dx
  19. L

    Discover a Game-Changing Sticky Expanding Liquid for Trapping Objects

    Hi I am new to physics and this website so forgive me if I am n the wrong section and kind of slow. Would it be possible to make some kind of sticky expanding liquid for trapping things in. I am thinking of a combination of quicksand and glue. This would be something that would be in a pit or...
  20. A

    The Expanding Universe: Evidence for Raisin Bread Baking Effect

    How do we know that the universe is more like raisin bread baking and not like all matter and energy leaving a central point? I somewhat understand the concept of space increasing rather than matter and energy just leaving the big bang, just wondering what evidence we have of this?
  21. X

    Expanding the electromagnetic hamiltonian

    This isn't a homework problem - I can't understand a particular statement in my professor's notes. As such, I hope it's in the correct forum. Homework Statement The Hamiltonian for a charged particle in a potential field A is \hat{H} = (1/2m) ( -i \hbar \nabla - q A)^{2} The square...
  22. T

    Is matter not expanding together with the rest of the universe?

    I was wondering, if the inflation of the universe can be compared to blowing up a baloon with, say, some ink dots on it representing matter, then, as the baloon grows in size, the ink dots should be getting bigger too since they are part of the same fabric. It does not seem to be the case in the...
  23. N

    What does SR say about the expanding universe?

    So from my understanding SR loosely tells us that time is not constant and that depending on our motion relative to another observer will dictate our differences in rate of time. I was wondering what SR tells us about the expanding universe. In cosmology we're taught that the universe is...
  24. J

    Limit to length of expanding spring?

    Imagine a massless compressed spring with its left-hand end anchored to x=0. Now I release the right-hand end of the spring. Within an interval of time each part of the spring will expand a certain amount. Thus the velocity of the spring at distance x should be proportional to x. Is...
  25. 0

    Relationship between expanding universe and time

    Some background: I am a senior in high school taking astronomy, so admittedly i do not know much about the structure and physics of the universe. However this is something that I've come up with on my own. I spend a lot of time just thinking about the universe, and this is one thing that just...
  26. S

    Lenz law wire and expanding loop

    Lenz law problem wire and expanding loop Homework Statement The loop has current radius R the red bar moves at velocity V. The distance the wire is from the loop is d and the top of the loop is length l Find the induced emf and the direction of the current in the loop. Homework Equations...
  27. A

    Is There a Center to the Expanding Universe? And How Does Light Factor In?

    Ok I have very little knowledge of all this but I was thinking about the expansion of the universe and light. First off the universe is expanding from every direction right so there is no centre but then is it andromeda that is supposed to be coming towards us. Anyway I was going to use that in...
  28. A

    Calculating Induced Current in an Expanding Loop

    Homework Statement Imagine a pliable round metal loop that can expand or contract. In a region with a constant magnetic field B0 that is oriented perpendicular to the plane of the loop, suppose that the loop expands, with its radius growing with time as r = r0(1+at2). As the loop expands and...
  29. A

    Magnitude of force within thermally expanding restrained bar

    Homework Statement A steel rod with a length of l = 1.55 m and a cross section of A = 4.52 cm^2 is held fixed at the end points of the rod. What is the size of the force developing inside the steel rod when its temperature is raised by ∆T = 41.0 K? (The coefficient of linear expansion for steel...
  30. B

    What are we expanding out into?

    For something to expand, It must have tangible boundaries that are growing. The ever expanding universe, thus must have boundaries. What is outside these bounds?
  31. J

    Is the total energy of each particle constant in an expanding universe?

    Assume that we have a particle i at rest according to co-moving coordinates. Then the total energy of the particle at rest, E_i, is its rest mass energy plus the sum of the (negative) gravitational potential energies between it and every other particle in the Universe. Thus we have \large...
  32. J

    Mechanism for matter creation in an expanding Universe?

    Hi, I wonder what people think of the following mechanism for matter creation in an expanding Universe. Imagine a particle-antiparticle pair coming into existence from the vacuum. As I understand it, they will annihilate each other in the time that a light signal takes to travel from one...
  33. C

    Newbie question about expanding universe

    Is our 3-dimensional space expanding because it is the "skin" of a higher dimensional space which is expanding? Is that why there seems to be no point of origin for the big bang?
  34. Tibriel

    Can We Pair Composition of Velocities with an Expanding Universe?

    Hi All, I get that one object can't travel faster than light with respect to another object because of SR and length and time contraction. What I don't get is how this meshes up with expanding universe. If the space between 2 objects is expanding then wouldn't two objects be accelerating...
  35. M

    Redshift and blueshift in expanding universe

    At first, people thought the universe was stationary. This seemed logical, why would any object tend to move in one direction or the other if there was the same amount of mass in all directions? Then they noticed the redshift of distant galaxies and concluded that the universe must be expanding...
  36. W

    FRW universe, expanding space or spacetime?

    In FRW universe, is space expanding or spacetime expanding? If the former... but I know that only spacetime can curve and expand. "Space" doesn't do that. Well?
  37. H

    Expanding in powers of 1/z (Laurent series)

    The textbook used in one of my courses talks about expanding functions in powers of 1/z aka negative powers of z. The problem is that I cannot recall that any previous course taught me/challenged me on how to expand functions in negative powers. For example, Taylor series only have positive...
  38. J

    My theory on expanding universe

    First let me start by saying thank you for taking the time to read this. On watching a program on the bbc relating to black holes and the comparison to a waterfall it got me thinking if matter was to fall through a black hole and be supper heated as it reaches the center if this is the case why...
  39. G

    Time and distance relative to an expanding universe

    As I understand it, the universe is approx. 14 billion years old. Light from the farthest observed galaxies took several million or billion years to reach us. Now my question is: If it takes for example, 500 million years for light from a certain galaxy to reach us it is 500 million light years...
  40. T

    Focusing an outside view (light) down a tube then expanding it

    Can someone please tell me if there is name for focusing the outside light to a point down a tube then magnifying it back showing the outside view? E.g. having the lenses focus on a hill side then focus down a 1 meter tube then enlarge onto wall. If there is no name for this what type of...
  41. D

    MHB Expanding f(z) with Powers of z-1

    How do I expand $\displaystyle f(z) =\frac{2z + 3}{z + 1}$ in powers of $z-1$?
  42. Q

    How exactly does light's wavelength expanding over time mean space expands?

    I already understand the notion, but what I don't get is how that leap is actually logical. Wouldn't you have to assume the photons and atoms are somehow "attached" to the fabric of space? It seems like the same thing as saying Earth's atmosphere is attached to it's crust.
  43. C

    How do we show that 2.2.19 and 2.3.21 are equal in this textbook?

    In this textbook, how exactly are 2.2.19 and 2.3.21 equal? http://i.imgur.com/LrcXE.png
  44. P

    Black Holes Relation to an Accelerated Expanding Universe

    Hello, Let me first start off by saying that I have no formal Education or background in Physics or Astronomy save for one course during college. This is simply posing an idea I had while reading an article on the acceleration of the expanding universe and how it could have a correlation with...
  45. S

    Is the Universe Expanding Into 4th Dimension?

    a)since universe is expanding is today's 1 meter different from tomorrow's 1m? b)since distant between any 2 points is increasing is the universe expanding into 4th dimension?
  46. E

    The diffence between expanding universe and light slowing?

    I am under the impression that the slowing of light over time would make the universe appear to be expanding. Is it possible that the permittivity or permeability of space has been decreasing over time giving the illusion of an expanding universe? Is there any way to test the differences and...
  47. Hepth

    Mathematically rigorous way of expanding propagators?

    Such propagators as found in HQET \frac{i}{2 v \cdot k} come about from expanding the full propagator. I'm wondering what the method is to properly Taylor expand denominators that contain 4-dimensional dot products. Lets start with something like : \frac{1}{2 v \cdot k + k^2} If we...
  48. S

    Expanding Universe: What We See & How We Know

    My question may be stupid, but as we look out into the universe aren't we seeing into the past? For instance let's say we are looking at a group of stars and they are 3 million light yrs away and moving away from us. Aren't they just moving away from us at that moment? Like the stars on the edge...
  49. J

    Expanding Universe-Colliding Galaxies?

    Ive heard the space between galaxies grows over time and that the universe is expanding in every direction..ive also seen the balloon explanation were they make dots on a balloon and blow it up to demonstrate the expansion of the universe, if this is true how is it we have colliding galaxies...
  50. B

    Wave Packet Expansion: Physical Reason & Conservation Laws

    Why do wave packets expand when they evolve in time? Is there any physical reason behind this? Is it a conservation law of some quantities that makes it expanded?
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