Scale Definition and 743 Threads

In the book "Statistical physics for cosmic structures" at p. 171 a read a definition of scale invariance (leading to the so called scale invariant power spectrum) given as the requirement that ##\sigma^2_M(R=R_H(t)) = constant##, where ##R_H(t)## is the horizon, i.e. the maximal distance that...

Hi guys, This question has me a bit stumped and I can't seem to find any methods on Google that would help me solve this: The last part of the question asks me to find the value of the scale factor, which in this equation I believe is 1.8. I know how to calculate percentage increases the...

Wabbit had an interesting comment in the "Aeon to Zeon" cosmology thread. Here's an excerpt, for more follow the link. I replied saying I'd start a separate thread.

Hey guys! I was reading the following paper http://arxiv.org/abs/hep-ph/0703260 for Georgi and I have a conceptual question about it. Howard Georgi was talking about this Unparticle Physics theory and at the base of his analysis is the principle of scale invariance. So Georgi is saying what if...

Homework Statement A 200g hamster sits on an 800 g wedge shaped block which in turn rests on a spring scale. An extra fine lubricating oil is sprayed on the top surface of the block, rendering it entirely frictionless, causing the hamster to slide down. Friction between the block and the scale...

Homework Statement (a)Sketch how the contributions change with time (b)For no cosmological constant, how long will this universe exist? (c)How far would a photon travel in this metric? (d)Find particular density ##\rho_E## and scale factor (e)How would this universe evolve?[/B] Homework...

I asked a question here in the forum, in the topic "Many Worlds Interpretation", things do touch in atomic scale? and in the macro scale? what defines "touching" ? Some members answered me.. Rodrigo Cesar said: in this video: watch?v=P0TNJrTlbBQ Professor Philip Moriarty explains it perfectly...

Homework Statement The energy density of the universe for radiation, matter and cosmological constant have changed over the years and there was a time (t), when it was equal for matter and radiation. Assuming the universe is 13.7 billion years old, estimate R(t) / R(0) where R(0) is the...

If say a hundred or more objects, at a human scale, are connected by a string, and they can be made to synchronize in an oscillation, could that be considered a bose einstein condensate?

Homework Statement Start from the 'relevant equation' below and derive $$ (1) \frac{\partial{\bf{\hat{q}}_{i}}}{{\partial{q}}_{j}}={\hat{q}}_{i}\frac{1}{{h}_{i}} \frac{\partial{h}_{i}}{{\partial{q}}_{j}}, {i}\ne{j}$$ $$ (2) \frac{\partial{\bf{\hat{q}}_{i}}}{{\partial{q}}_{i}}= -\sum...

Farraday's law tells us a magnet traveling through a solenoid will induce a current. It is understood electromagnetic properties and magnetic properties are somewhat interchangeable, and this allows magnets to move electrons in the wire. Can it then be inferred that an electron moving through a...

Unbelievable cheating in Indian schools. http://www.cnn.com/videos/world/2015/03/20/pkg-walker-india-student-cheating-scandal.cnn

Please be patient as I struggle with latex here ... Part 1 of the problem says to start with: $ \frac{\partial\bar{r}}{\partial{q}_{1}} ={h}_{1} \hat{q}_{1} $ and then to find an expression for $ {h}_{1} $ that agrees with $ {g}_{ij}=\sum_{l}...

In Bojowald's 2010 popularization of Loop Quantum Cosmology Once Before Time, there's a sketchy diagram (on his p.125) showing quantum perturbations in a transitional phase between contracting and expanding universes as widest at earlier times of decreasing volume, narrowing at the...

Hello, I have to estimate some values from a plot (shown in the attachment). The trouble is I'm not sure how to read one of the scales could someone please explain the nature of the scale along the top frame, the angular scale, i.e how it is spaced. One of my aims is to estimate which angle...

I know that scales measure weight (a force) via displacement of a spring. I also know the difference between a force and a mass. I know that, on the moon, the numbers on a scale might be different (depending on the answer to this question). I've read through the few threads on this matter here...

Hi, Could someone enlighten me in this matter? . how the calibration of cosmic distance scale affects the determination of the age of globular star clusters? thanks a lot :)

I am working on fixing a heavy walnut cedar chest lid that has bowed convexly from the chest. It is about 1/4" high in the center of a 24" deep lid. The lid is ~2' x 5'. It is made from 3/4" walnut with 3/4" x 3" ribbing on the top. I thought that adding in some C-channel or square tubing would...

Hello everyone. I'm studying the fixed point of theory in the context of QFT. First of all, let me say what I think I understood about fixed points and then I'll state my question. Suppose we have a theory with a certain running coupling ##\lambda(\mu)##. If we have, for example, an UV fixed...

Homework Statement A former student of mechanics wishes to weigh himself but has access only to a scale A with capacity limited to 400 N and a small 80 N spring dynamometer B. With the rig shown he discovers that when he exerts a pull on the rope so that B registers 76 N, the scale A reads 268...

Hello, I am looking for resources on scale symmetry including the persons who are at the forefront, arxiv preprints, history of the development of the idea, and any other sources you can think of. Thank you.

Homework Statement A chain of mass M and length l is suspended vertically with its lowest end touching a scale. The chain is released and falls onto the scale. What is the reading of the scale when a length of chain, x, has fallen? (Neglect the size of individual links.) Homework Equations...

You walk into an elevator, step on a scale, and push the "up" button. You recall that your normal weight is 625N. If the elevator has an acceleration of magnitude 2.50 m/s^2, what does the scale read? I know how to solve this problem, but I don't know why I'm getting the wrong answer. I first...

Hi there, This is my first post but I've been a spectator for a long time now. So I've been working on some of the basics of cosmic expansion and there is one contradiction that I came upon that I can't seem to resolve. I've looked around some of the similar threads but I couldn't find anything...

Hi.. I was reading some papers on continuum dynamics and its application to various material dynamics. The determination of macroscopic behavior is being studied , considering phononic interactions. As a material consists of phonons of various wavelengths, it is necessary to account for various...

Is it possible to build a fast, accurate scale using QTC? If so, could someone explain the basics or point me toward a good resource? Thanks!

Mod note: OP warned about not using the homework template. I have read that 'a(t) determines the value of the constant spatial curvature'.. Where a(t) is the scale factor, and we must have constant spatial curvature - this can be deduced from the isotropic at every point assumption. I'm trying...

Hi, I was wondering if anyone could refer me to a journal article that talks about the scale symmetric properties of renormalisation theory in the context of simple quantum-mechanical system governed by a delta function potential.

For my senior design project, I have to reduce the aerodynamic drag of a truck and trailer. I am doing CFD simulations and wind tunnel testing. The dimensions of the wind tunnel (test section) are 94 in long, 13.5 in tall and 20 in wide and a cross-sectional area of 270 in^2 and it could go up...

a question which is bugging me... Yes, I know that parity is violated only by the Weak Interaction, which is very short range. So I would answer "no, there is no P violation on macroscopic scale" However, many macroscopic properties are the results of what happens on the microscopic level. So...

In the FRW model with Euclidean 3-space, k=0 in the first Friedmann equation makes the density(times a constant) directly related to the Hubble parameter. The Hubble parameter is the time derivative of the scale factor divided by the scale factor itself. My question is: does a Euclidean...

I have a scale, the kind for weighing people, and I'm trying to calibrate it. It uses sliding weights, not springs. You step on the scale and then slide the two weights along the beam until it balances. Suppose I keep the smaller weight at zero and slide the larger weight to the 50-pound mark...

I see that Planck scale of mass-energy is related to the corresponding length scale by application of the uncertainty principle. What is not clear for me is how we find either energy or length scale to compute the other one? What goes wrong if we assume a higher energy level than the Planck...

Homework Statement What is the difference between the absolute thermodynamic temperature scale and the practical temperature scale: ITS-90? Homework EquationsThe Attempt at a Solution

Hi, I'm wondering what eigenvalue problem solver you are using? I'm looking for an one which could solve a very large eigenvalue problem, the matrices being ~ 100,000*100,000. Do you have any advices? Thanks.

Homework Statement You are standing on a bathroom scale in an elevator in a small building. The elevator starts from rest and moves with a velocity given by v(t) = (3 m/s^2)t + (0.2 m/s^3)t^2. If your mass is 64 kg what is your weight at t=4.0 s as recorded by the scale (in N) Homework...

Except for associating a statistical mean to a large number of measurements, how can one assign a single point to a particle ? Indeed, how can one assign a size of anything less than the Planck scale? A similar question about strings: how can one talk about one-dimensional objects? A similar...

In physics one often invokes arguments about a characteristic scale. For example at distances much larger than the Compton wavelength (a characteristic length scale) one might ignore quantum phenomena and calculate classically. I would like to read up some more on the thinking behind such...

Homework Statement Homework Equations $F=ma$ The Attempt at a Solution (a) Because the spring scale weighs 250 N, the effective weight on the child's side is 230 N. Therefore, $T-230 = \frac{230}{9.8} a$ and $T-250 = -\frac{250}{9.8} a$, so $a = 0.408$. This is correct, but is the...

I propose the Pauling Scale is not valid in all circumstances, and other scales of electronegativity would do better to predict the behavior of electron density in molecules: Electronegativity seems to be poorly defined for such a widely used chemical property: a 'tendency' of an atom or...

What's the scale on Mars rover Opportunity's "Microscopic Imager" images ? I'm trying to work out if the Martian "fossil" shown could be the impression of a cross-head-screw ... http://mars.jpl.nasa.gov/mer/gallery/all/1/m/3720/1M458433044EFFCEQKP2955M2M1.HTML

I wonder how can I get the data recorded on a scale be transferred onto a laptop directly? forexample, I need a curve in the change in weight of something in the past minute, I am looking forward to at least one measurement per second, preferably 10 per second or much higher. The recorded data...

Hello guys, I am doing a wind tunnel and I want to calculate the aerodynamic coefficient of some cars. To calculate this I need the frontal area of the car and I don't know how to calculate it manual. Is there any pc program to do it or any formula? Thank you very much.

I was lately interested in learning how the human body weight changes through out the day. Like, how much weight (may be in just 10s of grams) is lost during sleeping, after bathing, after workout and like that. For that I would require a highly precise scale. But most commercially available...

Do you know of any promising concepts for small scale fusion reactors (for electric power production)? I'm thinking of something the size of, say, a train car or even smaller.

Homework Statement I have an equation: dN/dt = N(r-a(N-b)^2) where r,a,b>0 are constants and I need to scale it to the dimensionless form dn/dtao=n(1-a(n-1)^2), however, I tried many ways and I am still unable to get it into the form. The question also suggests using n=N/c and tao=t/d as a...

I have built a model boat, ( http://schoolroad.weebly.com/rpgmodel_11.html ) and am trying to find out the amount of Power - maybe in Watts, that it takes to propel it at different speeds while it is running on the water. I have a rough sketch of the mechanism principle attached. When the...

Since Wilson work in the 70s, the renormalization technique in QFT is physically justified with the concept of scale dependence(scale anomaly) of the parameters. This apparently is akin to a universal version of the characteristic length usually applied to specific physical systems to define...

Homework Statement I'm not sure what I'm doing wrong on this problem! Please help :) Suppose that on a linear temperature scale X, water boils at -40.0°X and freezes at -174°X. What is a temperature of 146 K on the X scale? (Approximate water's boiling point as 373 K.) Homework...

How do I work out how many times more acidic a ph value of 6.8 is compared to 8.6? For example.