Expanding Definition and 637 Threads

Is there anyway to figure out the distance at which the universe is expanding (rate of stretching) at a rate that is equal to the speed of light?

Apparently the generaly accepted interpretation is that the expansion is speeding up, mainly by observing the redgarbageing of supernovae of distant galaxies and establishing their distance and redshifting indicating the speed at which they are moving away from us. The further away the faster...

Imagine a standard ruler (made of atoms) at the present epoch. Assume its comoving length is dx=x_1 - x_2 where x_1 and x_2 are the comoving coordinates of its ends at the present time. As the scale factor a=1 then its proper length ds=a \ dx is equal to its comoving length dx. Now imagine...

Hello all. I'm quite new to this forum. I was wondering about the expanding or stretching universe. Can someone please tell me if my thoughts are correct and if not please correct me. The expanding universe. A common definition of the universe is everything. But if the universe is expanding...

If light travels a metre in a unit of cosmological time now will it travel two metres in the same cosmological time interval when the universe has expanded to twice its present size?

When Hubble published that the galaxies were moving away from each other, the further away the greater redshift and the greater separation velocity, was he saying that space itself was expanding, on the basis of Einstein's general theory, or was he assuming a more or less fixed space, with...

Hey I'm 16 and currently studying my last year of physics in high school. I have to write an extended research task on a topic relating directly or indirectly to astrophysics. I have chosen to do the static universe theory vs the expanding universe theory. I've been researching as of late and...

Homework Statement Hey I have a question that I have to do that involves expanding a cubic. It is given in the form y = , once it is found I have to square it and then substitute it into a formula to find the area. All I need help with is the expansion than after that it's quite easy.Homework...

Okay, here's my problem. I've recently read that physicists believe that all the mass and dark energy in the universe do indeed add up to the critical density, which means that the universe will continue to expand forever, at zero curvature, and is either finite (like a torus) or infinite. And...

Hi, I'm new to the forum, and didn't really know where else to ask some questions, and get good answers, I'm fairly poor at mathematics, and grammar, but I have a passion for physics, astrophysics and cosmology. I have some niggling ideas and hypothesis that I can't find answers for, and I hope...

we all know the that the universe is exapnding. But where it is expanding?

What does it exactly means by the expanding of universe ? Does everything included in it is also expanding ??

Could one always write the periodic potentials in the form: v(r)=Ʃf(r-G) where the sum is over G (reciprocal lattice vectors)?

Hi Guys , Just read this at The NASA site: http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/070904a.html ""Q ...My question is if the universe is accelerating, eventually should it not reach a speed faster than the speed of light? Has anyone investigated the question as to what will...

Hey i am new to the forum but i have done some studying and I am trying to wrap my head around something but I am not sure if I am quite getting it i was hoping if someone could direct me to some reading or books, and so here it is, i was recently explained to that as the universe is expanding...

Perhaps the solar system is expanding with the Universe? For this idea to make sense one must assume that atomic lengths are constant. The current Universal expansion rate is given by: \frac{\dot a}{a} = H_0 where a is the current scale factor and H_0 is the current Hubble parameter...

Homework Statement Expand f(x) = 1 - x2 on -1 < x < +1 in terms of Legendre polynomials. Homework Equations The Attempt at a Solution Unfortunately, I missed the class where this was explained and I have other classes during my professor's office hours. I have no idea how to begin this...

I think in a piece by John Baez we learn that the physics of an expanding and collapsing dust filled universe is the same as the physics of a bouncing ball, Radius, R, verses time and height, h, verses time? If so are there counterparts to the kinetic and potential energy of a bouncing ball...

If f(x)=x+1, expand f(x) in Fourier series and hence show that \sum_{n=0}^\infty \frac{1}{(2n-1)^2}=\frac{\pi^2}{8}This question was set in an exam. I am in a position to try it if there is some interval say [-\pi \quad \pi] or like that. But there is no interval in the question. Please give...

Due to the doppler effect, when the source of the sound is moving away from the observer, the sound waves are spread out. Light waves also hace this effect and when a star or galaxy is moving away from us, we see the light wth a slight reddish tint. So my quesion is, does the expansion of the...

The comment, "The Event Horizon is expanding at the speed of light", has been used in posts in this forum. What is the justification or reason for the comment? It seems contadictory that a fixed EH radius could be moving. What is the EH expanding in reference to?

I have heard people say there is no center to the expansion of the universe. I have also heard the expansion described as an ever expanding balloon with all galaxies as dots on the surface. These to statements seem contradictorily to me. If the expansion of the universe was like the above...

There are 2 phenomena which I understand are more or less received wisdom (when seen from my pop science standpoint anyway). Firstly :space-time is ever expanding. Secondly:in a quantum "vacuum" matter/energy is continuously being created ( and disappearing) out of "nothing". Could...

Hi can I just check that i haven't done anyhting foolish here whe quantising the scalar field; \ddot{\phi} - \frac{1}{a^2}\nabla \phi + 3H\dot{\phi} - 3\frac{H}{a^2}\nabla \phi + m^2 \phi with \phi = \int \frac{d^3 K}{(2\pi)^{\frac{3}{2}}}(\chi \exp(+ikx) +\chi \dagger \exp(-ikx))...

Hi, I'm working on a problem stated as: Expand the following expression and simplify where possible $$ \delta_{ij}\delta_{ij} $$ I'm pretty sure this is correct, but not sure that I am satisfying the expand question. I'm not up to speed in linear algebra (taking a continuum mechanics course) -...

Hey all, Just to make it clear I am in no way a scientist or physicist but a mere space enthusiast. Yesterday I noticed when I was making some lunch that oil in my frying pan starts to ''run away'' from the center of pan towards outer side when heat gets just a little bit higher, since pan is...

Homework Statement Imagine some helium in a cylinder with an initial volume of 1 litre and an initial pressure of 1 atm. Somehow, the helium is made to expand to a final volume of 3 litres, in such a way that its pressure rises in direct proportion to its volume. (b) Calculate the work done...

Okay, so people say the universe is expanding like a 3 dimensional balloon. Now in the 2 dimensional balloon representation, it is curved so you will eventually end up in the same spot if you went in a "straight line" across its surface, like a planet. People also say that the universe most...

Can somebody explain to me why the temperature gets colder when expanding through a turbine versus expanding through a valve. Please explain with equations.

Hi, I have a quick question about making quantum mechanics relativistic by simply replacing the hamiltonian by a relativistic hamiltonian. If we write the hamiltonian operator as: H = \sqrt{P2c2 + m2c4}, schrodinger's equation in position basis becomes: i\hbar\dot{\psi} =...

Another question for you all. What evidence for an expanding universe is there besides redshift. I am a layman and to me it seems like it would be simpler to find another explanation for the spectral shift of light as it passes through millions of light years of space (say some kind of lensing...

Hello everyone. Let me introduce myself. I am Curious_Dude. Naturally, by nature, I am a curious person, hence the name. I rarely go on the forums, unless something really bothers me and I just MUST find out, and recently, this question hit me right in the head. This is not a homework...

Homework Statement I need to know how much the temperature drops after an inline heater which heats an airflow of 5 lbs/min up to 88 °C with an pressure of 54 PSI. When the air exits the heater it is released into the free air where it is 20 °C. I know that the air will expand to a...

ok, here it goes: this afternoon, wandering on wikipedia I stumbled across a 3D projection of a rotating tesseract I spent some time looking at it, then i started thinking about the universe. a bit of context: I've always been passionate for astronomy. I like to read about other planets and...

Hi, I have to write a spacetime line element for the shape of a cube of cosmological dimensions. This cube is expanding like this: i)With time, the cube becomes elongated along the z-axis, and the square x-y shape doesn't change. ii)The line element must be spatially homogeneus. (I don't...

I'm trying to understand the construction of the T(ε) operator and why it is equal to I-iεG/hbar. The textbook I'm using (Shankar) talks defines the translation operator with the phase factor: T(ε)\left|x\right\rangle=e^{i \epsilon g(x)/\hbar}\left|x+\epsilon\right\rangle and...

Romney Expanding the "Battleground" Presidential campaigning had been completely and eerily absent in Pennsylvania this season, but Romney is changing that. Campaign advertisements started yesterday (that I noticed) and he'll be campaigning in Philadelphia on Sunday. Obama has responded by...

I find the expression: "In general, one can expand the atomic displacements in terms of all the lattice wave modes (resembles a Fourier series expansion)" at: https://courses.cit.cornell.edu/ece407/Lectures/handout17.pdf But I have not found the expression in any other literature. (In fact...

Reading popular books (written by Hawking, Penrose, Greene, Linde, Guth and certainly many more) one finds numerous statements like entropy was low after the big bang ... Weyl-curvature hypothesis ... entropy increases with time ... black holes violate unitarity and therefore entropy or phase...

Im completing Engineering Maths cover to cover in an attempt to get more familiar with maths as I finished my education many years ago without really understanding many basic maths concepts. This problem is at the back of the introduction to algebra. (x-2y)^2 - (2x - y)^2 Now I can expand...

Hi, I've run into a problem with expanding algebraic functions via Newton polygons. Consider the function: f(z,w)=a_0(z)+a_1(z)w+a_2(z^2)w^2+\cdots+a_{10}(z)w^{10}=0 and say the degree of each a_i(z) is ten. Now suppose I wish to expand the function around some ramification point of the...

The idea of an expanding universe is said to be proven by using the calculated distance of a Cepheid star from us, and the amount of change in the wavelengths of light emitted from the Cepheid star relative to us. There must be another way to prove the universe is expanding since the...

I know that the Hubble constant proves this and scientist have done plenty of research on this topic. Today in my philosophy class we came about the topic of the universe expanding and the philosophy teacher and I were going back and forth on the subject of "How do you really know the...

The universe is expanding, I am told by a friend who is well-trained in such matters, not only in its spatial dimensions, but also in its time dimension. This sort of suggests that there is now more time between the beginning of time and yesterday than there was when it was actually yesterday...

Homework Statement A 95-g bullet is fired from a rifle having a barrel 0.540 m long. Choose the origin to be at the location where the bullet begins to move. Then the force (in Newtons) exerted by the expanding gas on the bullet is 16200 + 9400x - 23750x2, where x is in meters. (a) Determine...

Basically, all more distant galaxies have a Red Shift that increases with the distance to the galaxy, the Universe is expanding. 1) If there are other pieces of evidence that indicate the Universe is expanding, what are they? 2) Any internet links describing exactly how the other...

\pi = \frac{\partial \mathcal{L}}{\partial \dot{q}} = i \hbar \gamma^0 How do I expand i\hbar \gamma^0 the matrix in this term, I am a bit lost. All the help would be appreciated!

From answers given to me here and elsewhere, I finally got a (what I think should be the right) answer to the problem: Suppose that the universe were expanding in such a way that two planets were receding from each other at a constant speed of 1.1c (or, in other words, their distance would...

Homework Statement Consider a cylindrical piston in which an ideal gas is kept. The gas is currently at pressure P1, volume V1, and temperature T. The temperature T is assumed to be constant throughout the experiment. The piston is massless and frictionless. On the piston is a block of mass...

Now that I am making progress, I am ready to ask more complex questions :approve: Please correct me where my reasoning is wrong. Consider a cylindrical piston in which an ideal gas is sealed. The gas is initially at temperature T. The piston is well insulated, so that all thermodynamic...