What is Expansion: Definition and 1000 Discussions

Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions.Temperature is a monotonic function of the average molecular kinetic energy of a substance. When a substance is heated, molecules begin to vibrate and move more, usually creating more distance between themselves. Substances which contract with increasing temperature are unusual, and only occur within limited temperature ranges (see examples below). The relative expansion (also called strain) divided by the change in temperature is called the material's coefficient of linear thermal expansion and generally varies with temperature. As energy in particles increases, they start moving faster and faster weakening the intermolecular forces between them, therefore expanding the substance.

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  1. joshcitylife

    B Pressure on creation of the Universe

    I had a question today as a part of my studies which was 1) If space is ever expanding what is the pressure on the creating space (universe) upon creation and 2) at what rate might you assume the quantum field is also being created and is it being affected by this pressure of creation. This is...
  2. D

    I Can the expansion of the Universe reduce the energy of a photon to 0?

    Is it theoretically possible for the expansion of the universe to red-shift the energy of a photon all the way to zero? If so, what happens to the photon? Or does the photon's energy only approach zero as an asymptote?
  3. Kairos

    I Questions about the accelerating Hubble expansion

    I don't understand the discovery of "accelerating expansion" in 1998 (hence the postulate of dark energy, etc..), because Hubble's old law already described exponentially accelerating expansion in 1929, right?
  4. B

    I Inflationary vs deflationary phase of Big Bang

    Hi I'm a medical doctor, this is just a hobby my uncle got me interested in as a kid. If the universe is acceleration and galaxies are moving further apart, we assume the universe as a whole is expanding as a result. It's also projected to my understanding that eventually the universe will...
  5. ATT55

    Stress in cylinders due to thermal expansion

    I have two concentric thick cylinders in close tolerance (currently 50 micron gap), with a thin layer of glue between them. Internal cylinder is made from steel and external cylinder is made from ceramic (so the thermal expansion coefficient is not the same) The assembly is headed form inside...
  6. RChristenk

    Find the sum of the coefficients in the expansion ##(1+x)^n##

    ##(1+x)^n=1+C_1x+C_2x^2+C_3x^3...+C_nx^n## Let ##x=1##, hence ##2^n=1+C_1+C_2+C_3...+C_n## which is equal to the sum of the coefficients. I originally thought the sum of the coefficients would be ##2^n-1## since the very first term ##1## is just a number and has no variable. But apparently...
  7. Jaime Rudas

    I Relationship Between Expansion and Curvature in the Universe

    Orodruin said in another thread that "the spacetime of a spatially flat universe generally has curvature". Is the expansion (or contraction) of a spatially flat universe the manifestation of the curvature of its spacetime? If so, does the expansion correspond to a positive or negative curvature?
  8. E

    I Spacetime expansion - time dimension expansion

    I am trying to find some sources about time dimension expansion during spacetime expansion. Why do We assume that only spacial dimensions expand? I only found a lot of weird arguments. Btw, temporal dimension expansion does not mean that second was shorter in the past. Similarly to spacial...
  9. mister i

    B Where does the light energy lost due to expansion go?

    Sorry for my questions as an amateur interested in physics: If light changes its frequency during a long time of travel in space (vacuum?) for all observers (redshift) and therefore its energy decreases (E=hf), what "entity" absorbs this energy? I suppose the answer will be that the wavelength...
  10. mister i

    B Can the "creation" of space in the Universe affect the speed of light?

    Can the expansion/creation of space in the universe affect the speed of light over long distances? (dividing the space traveled (including expanded space) by the travel time). If the Hubble constant is valid throughout the universe, it follows that from a certain Megaparsec of distance, galaxies...
  11. S

    A Gravitational Instability and accelerated explanation of Universe?

    Ref: Principles of Physical Cosmology by P.J.E. Peoples, Princeton Univ. Press This question is likely fully answered somewhere, but I cant find it. Hubble obtained (1926) the mean mass density of the Universe as 10^-31 g/c.c. The gravitational stability equation gives (McCrea, Milne (1934))...
  12. D

    Engineering Thermal expansion of oil overflowing from a tank

    Just wanted to know if I was barking up the wrong bush or not with my working out if anyone could help?
  13. PhanthomJay

    I Understanding Space-Time Expansion: Debunking the Myth of Non-Physical Space

    How can space expand when space is not a physical thing? I’ve heard some say that is not expanding but rather it is getting less dense, which to me implies the same thing.
  14. sjordannc

    I What was expansion speed at the time of the CMB?

    To be clear, I'm looking for the speed at which points in space were moving apart from one another in the universe as it existed 370000 years after the big bang, not the Hubble parameter (expansion rate) derived from our current distance within our current time. Thanks in advance!
  15. S

    B How did expansion take 380,000 years to let light travel freely?

    Here's as far as I've gotten in the research (please correct any errors I'm making). The stages of high density had included these periods: • light at high energy was in a cycle of forming into matter, forming back into light, and so on • until things cooled enough for nucleons to form •...
  16. S

    I Result of this integral in large Lambda limit

    $$\int \text{d}^4 q \, \frac{1}{(q^2 + m^2)\left(1+\frac{q^2}{\Lambda^2}\right)^2} =2 \pi^2\left(\frac{\Lambda^2}{2}-m^2 \log \frac{\Lambda}{m} \right) + o(\Lambda^0)$$ How to get this result? The notation ##o(\Lambda^0)## means all terms constant in Lambda, which we ignore because we are...
  17. E

    I Is the expansion of the universe affecting time or just space?

    I read this old thread: https://www.physicsforums.com/threads/what-happens-to-time-as-space-is-expanding.1001016/ And I am confused by the responses. When I consider time dimension expansion, I perceive it the same way as space dimension expansion. The expansion doesn't change the unit size...
  18. J

    B Expanding Universe -- What is it expanding into?

    I believe in the Big Bang but I struggle with something. If the Big Bang happened and universe is expanding there has to be something (or really nothing) there for the universe to be expanding into. Any thoughts?
  19. S

    Is Thermal Expansion Fatigue a Concern for Aluminum Alloy Motorcycle Frames?

    Hello, assuming to keep an aluminum alloy motorcycle frame not in use, still, will the daily temperature variations cause thermal fatigue due to the continuous expansions and retractions or is the force developed by a few degrees of variations not sufficient to create microstructural dislocations?
  20. Reuben_Leib

    I Why does ##u## need to be small to represent the Taylor expansion

    Necessary condition for a curve to provide a weak extremum. Let ##x(t)## be the extremum curve. Let ##x=x(t,u) = x(t) + u\eta(t)## be the curve with variation in the neighbourhood of ##(\varepsilon,\varepsilon')##. Let $$I(u) = \int^b_aL(t,x(t,u),\dot{x}(t,u))dt = \int^b_aL(t,x(t) +...
  21. J

    I Universe Expansion: GR vs Hubble Reconciled

    The GR predictions for the universe's size are those of fig.a. Whereas the Hubble expansion is exponential, fig.b. How are the two reconciled?
  22. E

    I Bra-Ket Notation Manipulations: Quantum State Expansion

    I suspect it will help if you know about my background: I did some linear algebra in university but never used it and am now in my mid 60s. I am interested in understanding the mathematics of quantum physics. I have read a number of layman's texts on quantum mechanics, but they all gloss over...
  23. C

    Thermal expansion of square from temperature increase of 50K

    For this problem, The solution is, I understand their logic for their equation, but when I was trying to solve this problem, I came up with a different expression: ##\Delta A = \Delta L_x\Delta L_y## ##\Delta L_x =\Delta L_y = \Delta L## since this is a square. ##\Delta A = \Delta L^2##...
  24. elcaro

    I Cosmological expansion of space - question

    I the lambda-CDM model, is the expansion of spacetime uniform around all of spacetime, is there a smooth transition between expanding parts of spacetime (the voids) and non-expanding parts of spacetime, or is there a sharp distinction between expanding and non-expanding parts of spacetime. Is...
  25. M

    I Expansion of the Universe and the cosmological principle

    Wikipedia states the following in their article about the expansion of the universe: If the cosmological principle was discovered to be false in our universe, i.e. our universe was discovered to be inhomogeneous or anisotropic or both on very large scales and the FLRW metric does not hold for...
  26. Bandersnatch

    A Black hole mass coupled to expansion -- astrophysical source of dark energy?

    Observational evidence for cosmological coupling of black holes and its implications for an astrophysical source of dark energy Comments?
  27. S

    I Expansion at first order in QCD counterterm

    What is the meaning of the expansion at first order in ##\delta_2## and ##\delta_3## at the second step in the last line? These quantities are not "small" - on the contrary, the entire point is to then take the ##\epsilon \to 0## limit and the counterterms blow up
  28. M

    I Adiabatic expansion work far exceeds isobaric of same volume, why?

    Using the adiabatic process formula, I've calculated the change in volume for a volume of gas with an initial pressure of 10 psig expanding to 0 psig. The initial volume is 100 cubic inches and the expanded volume is 144.9. This is a difference of 44.9. The total work done ends up being about...
  29. L

    I Taylor Expansion Question about this Series

    Can you please explain this series f(x+\alpha)=\sum^{\infty}_{n=0}\frac{\alpha^n}{n!}\frac{d^nf}{dx^n} I am confused. Around which point is this Taylor series?
  30. P

    I Vector Potential Multipole Expansion

    when you do a multipole expansion of the vector potential you get a monopole, dipole, quadrupole and so on terms. The monopole term for a current loop is μI/4πr*∫dl’ which goes to 0 as the integral is over a closed loop. I am kinda confused on that as evaulating the integral gives the arc length...
  31. L

    B The collision of molecules during thermal expansion

    Greetings everyone. I learned that the distance between molecules in liquid increases while the temperature increases. Hence, its density is decreased. The process is thermal expansion. At the same time, the collision between molecules would be more frequent when the temperature increases...
  32. crakedhead

    B Why the expansion after the "Big Bang" is showed in cylindrical form?

    Everywhere on the net, there is no image that the expansion has a departing point, through an expansion in spherical form... Why is that?
  33. C

    Free expansion of Real Gases - Dieterici EoS, Change in Temperature

    I proceeded in the usual manner in which we take ##dU = 0## in the case of free expansion because there is no heat transfer in the box, as well as no work is done. We can write, taking ## U ## as the function of ##V## and ##T##, $$ dU(V,T) = \left( \dfrac{\partial U}{\partial V} \right)_T ~...
  34. Ahmed1029

    A Free expansion of an ideal gas and changes in entropy

    For a freely expanding ideal gas(irreversible transformation), the change in entropy is the same as in a reversible transformation with the same initial and final states. I don't quite understand why this is true, since Clausius' theorm only has this corrolary when the two transformations are...
  35. S

    I Can there be some kind of photon emission caused by space expansion?

    Are there any kind of observed and experimentally verified processes or mechanisms where photon emission occurs and which are directly cause by spacetime expansion in some way?
  36. T

    A Understanding Free Expansion of Gas: Velocity Distribution Function Evolution

    Hey all. I'm trying to understand the evolution of the velocity distribution function of a gas undergoing free expansion. I know that at t=0, the velocity distribution function is given by ##u(t=0, x)=Ax^{1/2}##, where ##A## is a known constant. From the momentum equation, I have: ##du/dt+u...
  37. H

    I Exploring Work Done in Quasi-Static & Non Quasi-Static Expansion

    I'm wondering what's the difference between work done on quasi-static and non quasi-static expansion. In a quasi-static process, the gas inside the system must do a work to "extend". However, in a non quasi-static process, where the gas inside the system doesn't move fast enough to "push" the...
  38. EddieP

    Thermal expansion of air bubbles in plastic

    I am interested in the potential for air bubbles in a plastic structure to expand with heat, and put pressure on the plastic surrounding the air bubble. In this case the plastic structure is formed by melting a thermoplastic powder. In between the grains of powder are voids with air in them. As...
  39. I

    B Distance of Stars / Size of the Universe calculation

    Hi, I am a new user, This question is bothering me for a long time and now with all the Webb telescope hype I need to ask: It sounds very logical to think that a star that is a billion light years away is seen as it was a billion years ago because the light took 1 billion years to get here...
  40. Onyx

    B Sign of Expansion Scalar in Expanding FLRW Universe

    Considering the FLWR metric in cartesian coordinates: ##ds^2=-dt^2+a^2(t)(dx^2+dy^2+dz^2)## With ##a(t)=t##, the trace of the extrinsic curvature tensor is ##-3t##. But why is it negative if it's describing an expanding universe, not a contracting one?
  41. T

    B Expansion of Space Itself, rather than due to an Explosion like the Big Bang?

    Please explain how we know that it is space itself that is expanding rather than an expansion due to an explosion such as the big bang. In either case wouldn’t every object appear to be moving away from us? How do we determine that space/ time is expanding? Tex
  42. W

    I Relationship between geometry and expansion rate

    As I understand it, the flatness problem of Bob Dicke, says a flat universe in unstable and so has to be set very precisely in the early universe to give us the flat universe we see today. Is this the same problem as saying the expansion rate had to be finely tuned and if so how are the two...
  43. Simon Peach

    B Bound Systems in an Expanding Universe: How Can Galaxies Merge?

    As the universe expands all objects are moving away from us, so how is it posible that the Andromeda galaxy is on a path to merge with our galaxy?
  44. S

    I Mining the Universe's expansion?

    There is an article written by astrophysicist Edward Harrison [1] which defends that energy could be extracted from attaching an imaginary cosmologically long string to a receding object from us in an expanding universe. He says that the energy extracted is potentially limited (in decelerating...
  45. S

    B Spatial Expansion -- Coincidence?

    I was trying to follow how Hubble constant supposedly works. If it is about 70 km/sec/Mpc, then the the expansion at 13.8 Bly distance is about the speed of light. That, if I got it right, seems too convenient don't you think. I know it's not the same start to finish. Thanks if you can correct...
  46. svenz706

    A Non-minimally coupled inflation — expansion

    Hello, In the Wikipedia article on "Inflaton" there appears the following formula: ##S=\int d^{4}x \sqrt{-g}[ \frac{1}{2}m^2_{P}R-\frac{1}{2}\partial^\mu\Phi\partial_{ \mu }\Phi-V(\Phi)-\frac{ 1 }{ 2}\xi R \Phi^]## with ##\xi## representing the strength of the interaction between R and...
  47. Arman777

    A Series expansion of ##(1-cx)^{1/x}##

    I am trying to understand the series expansion of $$(1-cx)^{1/x}$$ The wolframalpha seems to solve the problem by using taylor series for ## x\rightarrow 0## and Puiseux series for ##x\rightarrow \infty##. Any ideas how can I calculate them ...
  48. berkeman

    SpaceX says 5G expansion would make Starlink 'unusable' for most Americans

    Is this something to pay attention to, or just some big companies posturing against each other? SpaceX says 5G expansion would make Starlink 'unusable' for most Americans
  49. F

    Link between Z-transform and Taylor series expansion

    Hello, I am reading a course on signal processing involving the Z-transform, and I just read something that leaves me confused. Let ##F(z)## be the given Z-transform of a numerical function ##f[n]## (discrete amplitudes, discrete variable), which has a positive semi-finite support and finite...
  50. M

    I Expansion of Space: Questions on How the Universe Works

    I first apologize if this has been posted more than once; sorry. There is a lack of clarity at my end as to whether I am logged on here? Say we have two galaxies, the Milky Way (MW) and galaxy A separated along a straight line 20 x the radius of the Universe visible to us. If I understand...