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. 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?
  2. gttjohn

    Why is the universe expanding?

    can anyone tell me why is the universe expanding faster and faster and not slower and slower or moving at a constant speed ,if a bomb explodes everything close to it accelerates away then slows down as time moves on ,in the void of space i would think things would just carry on expanding not...
  3. D

    If the universe is truly expanding, why aren't any stars getting dimmer?

    The intensity of light observed from a given source decreases as the square of the distance between the observer and the source. Hence, if stars are truly receding from the earth, the intensity of light observed from any such star should be getting dimmer as time goes by. But the intensity of...
  4. nearc

    Computer simulations of expanding space

    i'm looking for computer simulations of expanding space. i made a couple of very very very simple models and my results were no where near our current model of space. hence, I'm looking for work that has already been done on the subject.
  5. M

    How to find that the universe is expanding from general theory of relativity

    1 how to find that the universe is expanding from general theory of relativity 2 how to apply general theory of relativity to find that the universe is expanding
  6. C

    Expanding Power Series for (x+x^2)/(1-x)^3 | Simplification Techniques

    Homework Statement Expand f(x)= (x+x2)/(1-x)3 Homework Equations ? The Attempt at a Solution I've tried everything I can think of to simplify this equation: substitution of various other power series, partial fraction decomposition, taking derivatives, multiplying out the...
  7. W

    How is the universe expanding?

    I was wondering because of my personal theories what others thought of the universe expansion. please help
  8. J

    Question about planck lengths/quantized space and expanding space?

    If I'm not mistaken, it is thought that space is divided up into quantized little indivisible chunks, the size of which is called the Planck length. Also, the space of the universe is thought to be expanding. We could have 2 objects stationary relative to one another at some time t_0, then...
  9. J

    Proof of expanding algebraic functions by Puiseux series

    Hi, I'm told that a basic result in algebraic geometry is that all algebraic functions w(z) of one variable given by the equation: f(w,z)=a_n(z)w^n+a_{n-1}(z)w^{n-1}+\cdots+a_0(z)=0 can be written in terms of fractional power series of the form: w(z)=\sum_{n=-\infty}^{\infty}a_n...
  10. K

    Is Our Expanding Universe the Result of Black Holes from Other Universes?

    The other day I saw Michio Kaku saying scientists now think that the universe "may have" started from being puked out by a black hole from another universe. If this is correct could the answer to the question " why is the universe still expanding" be " It is still expanding because the said...
  11. G

    Ant Motion on an Expanding Balloon: A Paradox?

    This isn't homework but nobody is going to believe that so here it is: Homework Statement at t=1 (or any nonzero value of t) an ant starts moving across a balloon at velocity v=c=1 (c is the speed of light) the radius of the balloon as a function of time is given by r(t)=nct (n is a...
  12. D

    Expand (x-μi)ᵀΣ⁻¹(x-μi) Homework

    Homework Statement I need help with expanding: (\bf{x-\mu_{i}})^{t}\Sigma^{-1}(\bf{x-\mu_{i}}) \bf{x,\mu_{i}} are column vectors. \Sigma is a square matrix. Thank you. Homework Equations Can: \bf{x}^t\Sigma^{-1}\bf{\mu_{i}} be written as...
  13. E

    What makes Dark Energy cause Acceleration of the Expanding Universe?

    According to Misconceptions about the Big Bang in Scientific American by Charles H. Lineweaver and Tamara M. Davis, space-time is expanding and carrying galaxies with it, rather than galaxies being moved ever faster and further into space-time. See...
  14. A

    How do we know the universe is expanding?

    Im very new to astronomy and astrophysics, so this may be a very simple question. I read somewhere that astronomers observed that galaxies further away were moving away at a faster speed than galaxies closer to us. Hence, the universe is expanding at an accelerated rate. However, when we...
  15. S

    Temperature drop in an expanding gas?

    Hi, I'm prototyping a non electrical refrigeration system and need some help with a calculation. I have a 2 litre bottle. I pump in air until the internal pressure is 5 bar. I allow the heat increase to dissipate back to the ambient 20 C. I release the air. What will the temperature of...
  16. O

    Question: What is the Universe Expanding Into?

    It may be a silly question , but sometimes I ask it to myself : If the universe is expanding , throw what is it expanding ? There is no "place" because the place itself is expanding , and there is nothing at all , so how can galaxies become far and far from each other ? If the place is the...
  17. C

    Expanding Space: Explaining the Mystery

    This might be in the wrong section. If all the matter and energy in the universe was localized into a small region at some point in time. why would it expand, the gravitational field would seem to be very strong and prevent this. But then I think they say that space itself is expanding, OK but...
  18. C

    Spacetime expanding within galaxies?

    I understand that spacetime is expanding between galaxies, as seen with the cosmological redshift. But, is it also expanding inside galaxies, such as the Milky Way? I'm not sure if the galaxy is gravitationally bound enough to where spacetime might actually be contracting within the galaxy...
  19. R

    Value of a measuring rod in an expanding universe?

    I have a question, but I'm a neophyte so please correct my premise if it is wrong. If it is true that in an expanding universe the space between any 2 points increases than wouldn't it be true that the space between the end points of a measuring rod (e.g. a light year, or more fundamentally a...
  20. R

    If Universe is Expanding at an Accelerated Rate Why

    Why are objects still the same distance apart? The sun is still roughly 92,900,000 away and the last time I checked Proxima Centauri was still about 4.2 years from us. I know this is a dumb question, but I am just a layman, although a fascinated layman.
  21. R

    Is the Expanding Universe Theory Reversed? A Scientist's Perspective

    I have read a few threads on here and acknowledge i am way out of my depth. Bearing in mind my limited knowledge can someone explain to me how we can say the universe is expanding now. the logic seems reversed to me. I've heard it as the furthest away galaxies are receding from us at the...
  22. J

    Question about work done by expanding pressurized gas

    In my thermodynamics class, we were shown an equation that gives the work done by expanding pressurized gas given as the integral from v1 to v2 of C/V*dV where C is a constant and v1 and v2 are initial and final volumes respectively. My question has to do with the fact that this is basically...
  23. D

    Does expanding space affect time dilation etc?

    In special relativity we have the velocity 'u', being the difference in speed between two objects, from which we work out time dilation, length contraction etc. But if those objects are separated by some expanding space, but not moving with respect to that space, is there still the dilation...
  24. T

    Collision of an expanding disc with another disc.

    Hi, Like a lot of people programming, I created a simplistic 2D collision engine. This engine handles the collisions of circles (I know I typed "disc" in the title, but I wanted to avoid replies like "circles don't really exist so they can't collide".) The simulation is friction-less, so...
  25. JK423

    Expanding a ket in the basis of different Hamiltonians

    I have the following very basic question, and i'd really like your help! If we have a system, that is described by a Hamiltonian H, then we can expand the state of the system to the basis of H. And we say that, if we measure the observable H the state will collapse to one of H's eigenstates...
  26. Z

    Expanding Universe vs. Shrinking Matter

    After reading about the expanding universe, and the balloon analogy, I found myself wondering about some things. Like many in these forums, I found it difficult to get my head around the concepts. At first I wondered, if space is expanding, and the distance between galaxies is increasing, then...
  27. P

    Is the Universe Really Expanding?

    so, many shows on tv today that keep suggesting our universe is expanding. is it really? 1. if you can say "it is expanding" doesn't that imply you 1st have to know how big it is now, then make a observation (measurement)? so if the universe is already infinite in size how can anyone say its...
  28. S

    Calculating Coordinates on an Expanding Globe: An Exploration of Time Theory

    Homework Statement how can i calculate a co-ordinate on an ever increasing sized globe, where i do not know the circumference or diameter. the only constants i am aware of are my starting point, pi and how far i wish to travel. i figure that if time is an ever expanding globe, and not...
  29. A

    News Icy, calculating ABB used expanding bullets forbidden in warfare

    Probably in order to maximize damage to his victims, Anders Behring Breivik had hoarded so-called "dum dum" bullets, i.e hollow bullets that expand when entering the target's body. These bullets are prohibited by just about every international convention regarding legitimate warfare...
  30. B

    Expanding Mathematica code from 2 dimensions

    I have this mathematica code to solve a variation of the 2 Dimensional Poisson's equation using the finite difference method. xo = .5; yo = .5; \[Sigma] = .05; q = 1; Gen[x_, y_] := -q*E^-((((x - xo)^2) + ((y - yo)^2))/(2*\[Sigma]^2)); GridNum = 300; Hstep = N[1/(GridNum + 1)]; GridPts...
  31. S

    The universe is expanding wait, really?

    As you might have guessed from my subtle hint, I've been pondering the nature of dark energy and its involvement in the expanding universe and I tripped over a stupidly simple alternative idea that pretty much changes much of what I understand about cosmology since the times of Albert Einstein...
  32. A

    The impossibility of any life due to an expanding universe and entropy

    Hi All, I'm a newbie here and I don't know enough about physics to answer my question, so I will submit what I think I know to be true, then pose some questions, therefore please pardon any allowable mistakes. 1) Time is immaterial for my purposes in this posting, at least in a...
  33. S

    Expanding functions in increasing powers

    I have not been taught how to do this and therefore unable to answer the following question :- Expand the function f(x) = (1+x)^3 in increasing powers of x ? Please help
  34. A

    Induced current in expanding metal ring

    Homework Statement A circular metal ring, as shown on the diagram below, is constructed so as to expand or contract freely. In a region with a constant magnetic field Bo oriented perpendicular to it, the ring expands, with its radius growing with time as r=r0(1+\alphat2). As the ring expands...
  35. Y

    Question about dark matter gravity and the expanding universe.

    My question/thought is this... We know gravity is related to matter, could dark matter have "anti-gravity" Just like magnets have different polarities, one to attract and one to repel, could gravity have similar properties that we are unable to identify, perhaps related to types of matter...
  36. R

    What effect does the expanding universe have on spacetime?

    If our universe is indeed expanding, would this have an effect on spacetime? For example as space and time are related, if I change one, shouldn’t it have an effect on the other? Also, wouldn’t it make gravity weaker as it is stretching space?
  37. Y

    What is Expanding Horizon of a black hole?

    What is Expanding Horizon of a black hole? Recently, I want to read something general on Expanding Horizon...
  38. B

    Expanding the Range of an Electrometer?

    If i have and electrometer. How can i safely increase its range from the 100V to the 10kV range. The electrometer has ultra high resistance so whatever i added in the circuit would need that too. Any ideas?
  39. M

    Exploring the Expanding Universe - Nova Documentary

    i've seen many documentaries. most recently nova had one on the expanding universe which prompted me to send them (nova@wgbh.org) the following: based on the nova shows I've seen, they suggest the universe is expanding. farther objects are observed as moving away faster than closer objects...
  40. R

    Does the expanding universe contradict relativity?

    I know this is probably a stupid question but I was wondering, with two frames that are moving wrt to each other, it is valid to say that ‘A’ is moving from ‘B’ OR that ‘B’ is moving from ‘A’ However with the expanding universe, I can say that all other frames are moving away from me, but I...
  41. A

    Expanding knowledge on the Classical Groups

    I need some material on the properties and relationships between classical groups. I was using Robert Gilmore's "Lie Groups, Lie Algebras and Some of their Aplications", but it barely covers it (section 2.iv). Does someone know about a book or any lecture notes that could be used to...
  42. H

    Could the Laws of Physics Change in a Universe with Different Matter Density?

    ...why aren't the laws of physics changing ? Gravity for example works on a formula dealing with the inverse square of distances. If those distances are changing, why isn't the law of gravity changing ? Or indeed everything. Anybody have a simple answer ? Ta.
  43. FeDeX_LaTeX

    What an Expanding Universe Looks Like

    Hello; Please forgive me if this is a silly question, or if it's been answered before. I have tried googling this, but I can't find the information I need, I've probably overlooked it, but I can't find it. I recall a quotation by Lawrence Krauss who said in a talk that "from the inside...
  44. R

    Programming Orbit Expansion: Change Radius w/ Centripetal Force

    I am programming a game that involves objects orbiting in 3d space circularly around an axis. I have the orbits working for a fixed radius using centripetal forces, however, I want to be able to change the radius while the program is running. I have tried to just make the magnitude of the...
  45. C

    How to show that the universe is static( not expanding)

    Homework Statement how can i show the universe is static and not expanding, how it really is. Homework Equations \OmegaM=... \Omega\Lambda=... The Attempt at a Solution "The expansion history of the universe depends on the amount of matter (gravity), quantified by \OmegaM...
  46. D

    Infinity corrected lens - expanding before tube lens?

    Hello folks, I am on a project that involves combining Raman microscopy + optical tweezers, and I made a setup over the past year. All of this is home built on minimal funds so its not the neatest of all setups. It involves an upright microscope (coupled to trapping laser) and collecting the...
  47. R

    As the universe is expanding light from further away it goes towards

    As the universe is expanding light from further away it goes towards the red end of the spectrum but will there ever become a point theoretically that it shifts so far it'll go off the red end of the spectrum and we wouldn't be able to see it
  48. C

    Question about theory of expanding universe

    New to cosmology, please go easy on me. ;) 1. REFRACTIVE INDEX "It is generally accepted that the speed of light in a vacuum is not dependent on its frequency (color)." http://accessscience.com/studycenter.aspx?main=17&questionID=3781 2. IS SPACE A VACUUM? "Outer space (often simply called...
  49. K

    Expanding Binomials: Simplifying Complex Expressions

    Homework Statement by expanding the binomial show that ( (Sqtroot(3)/2) + (1/2)i )^4 = ( (-1/2) + (sqroot(3)/2)i ) The Attempt at a Solution I'm stuck, I now ( (Sqtroot(3)/2) + (1/2)i )^4 = ( (9/16) + (1/16)i ) But that's all I got, don't know the next steps.
  50. K

    Exploring Energy Sources for a Refuge in an Expanding Universe

    Dear All As I have understood, there will be only cooling chunks of matter like stray planets, neutron stars, brown dwarves and all other kind of debris left of our Universe in 10^20 years, which continue drifting apart as the Universe expands on (let us assume that it does). They will...
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