Flat Definition and 469 Threads

hi, I am a bit confused on what the current model of the universe is. some are saying it is round, while others are saying it is flat. which is true? If the universe is flat, then is it that only some part of it is flat or the whole universe is flat? how can we prove it theoratically...

for estimating Pn...

I'm asking because some of you state that flat spacetime can't model black holes... meaning even between the Planck scale and event horizon, but yet atyy said spin-2 field in flat spacetime is equivalent to General Relativity for spacetime that is covered by harmonic coordinates which atyy...

It is said that minkowksi spacetime is flat. How about galilean (Newtonian) spacetime, is it flat too? If not, what is it? It is also said that it is unknown whether there is geometry or spacetime inside Planck scale. If there is none. I can't imagine how the Planck scale without geometry can...

Hi, does flat spacetime + gravitons automatically lead to curved spacetime? In an old 2002 google thread sci.physics.research which is moderated...

I'm uneducated in Physics so I'm not sure where to begin with this. I want to build a vacuum chamber that is rectangular and fairly flat. It will measure 48"X96"X8" I plan on constructing it from clear polycarbonate sheet on one face (would clear acrylic be a better choice?) and aluminum sheet...

Just a introduction to my project, I have designed and building a 69 Volkwagen Bug with a Version 8 subaru Sti Engine, The pan is built with tube braces and coil over suspension, I built a tall back bone frame for strength and for the rest of the frame to be lower for ride height and suspension...

Homework Statement Two identical flat capacitors with no dielectric material inside are connected in series to a voltage source. The electric field intensity inside the capacitors is E. If the space inside one of the capacitors is filled with a dielectric material of ε=9 how strongly did the...

"Flat Universe"question. Hello, everyone! I'll start by saying that astronomy or physics are not my majors here; I'm a freshman Med School student, however I've recently started amateur astronomy as a hobby. Naturally I had to increase my knowledge on this subject so I started visiting...

Hi there. I have a current I running throught a tesla spiral coil, and I have to compute the magnetic field at the center of it. The tesla coil has N turns, and an inner radius a, and outer radius b. This is the tesla spiral coil: The courrent enters through the outer cable, and goes out...

I'm writing a paper for a philosophy elective on the Cosmological argument. One of my counter arguments is that a causal loop (treated as a paradox in the Cosmological argument in favor of a creator) is not a paradox if time is cyclic in nature rather than linear. I treat the fact that the...

Is the following true ? In flat space, we have a familiar doppler shift formula for two observers moving relative to each other. Suppose they had a relative ,constant acceleration between them.Then their relative velocity is changing with time. Will the doppler shift formula still hold with a...

Nice article in 'The Economist' on how Republican candidates are competing to race to the lowest point: http://www.economist.com/node/21534799 With a candidate Romney/Cain/Perry and all their lunatic tax reform proposals, I can not possibly imagine how the Republicans will beat Obama next...

Homework Statement Establish the theorem that any 2-dimensional Riemann manifold is conformally flat in the case of a metric of signature 0. Hint: Use null curves as coordinate curves, that is, change to new coordinate curves \lambda = \lambda(x0, x1), \nu = \nu(x0, x1) satisfying...

Homework Statement Is a spring longer hanging or flat on a table? Homework Equations logic. The Attempt at a Solution I think the answer would be hanging because then the mass of the spring pulls it down a bit, thus stretching it more than when it is flat.

Homework Statement Two blocks mA= 5.0 g and mB= 10.0kg are connected to a string. Both blocks sit on a smooth inclined surface where the angle on the inclined plane is 30.0°. Block A is about block B on the incline. Find the acceleration of the system of two blocks. What is the tension TB in...

Homework Statement A nearly flat bicycle tire becomes noticeably warmer after it has been pumped up. Approximate this process as a reversible adiabatic compression. Take the initial P and T of the air (before it is put into the tire) to be 1.00 bar and 298.0K. The final volume of air (after it...

Homework Statement See figure attached. Homework Equations The Attempt at a Solution My professor came up with this example in lecture and the way he went it about it was very confusing so hopefully you guys can help me clear up some of steps/thought process he took. We are...

Suppose that you have a sheet of copper that carries a surface charge of \sigma on each face. The electric field just outside of each face can be calculated by plane symmetry and the solution would take the form E=\frac{\sigma}{2\epsilon_{0}}\hat{n} correct? If not I have to go back and...

Homework Statement In a laboratory experiment two spherical balls are launched on a °at surface. Both are uniform spheres of radius R and mass m. They are both given the same amount of initial kinetic energy K0. However: -ball A rolls without slipping -ball B slides without rotating...

Homework Statement The mass of the homogeneous flat plate is 50 kg. Determine the reactions at the supports A and B. I've attached the diagram. The Attempt at a Solution I know I will need to find the center of mass. I don't remember exactly how to do it, but I found the centroid...

trying yo figure this out: the graph of stress concentration factor K for flat bars with a circular hole geometries are shown in the diagram link below. a load of 50kN is applied to the plate. the width of the plate b=100mm with a thickness of t=10mm find the maximum stress for the...

Hi, I'm trying to carryout some analysis of flat plates subjected to hydrostatic water pressures however the plate material is HDPE. The problem I'm having is that all the formulae on the web and in Roark's 7th Edition are typical of steel with a Poisson's ratio of 0.3. I can't therefore...

Hi there! I'm new here and am currently looking into the Hartle-Hawking and Hawking-Turok Quantum creation models. What I've read about the Hartle-Hawking model is that it predicted a Closed Universe. But isn't that the opposite of what we have learned? The WMAP sattelite has confirmed the...

Let us consider the General Relativity metric: {ds}^{2}{=}{g}_{00}{dt}^{2}{-}{g}_{11}{{dx}_{1}}^{2}{-}{g}_{22}{{dx}_{2}}^{2}{-}{{g}_{33}}{{dx}_{3}}^{2} ---------------- (1) Using the substitutions: {dT}{=}\sqrt{{g}_{00}}{dt} {dX}_{1}{=}\sqrt{{g}_{11}}{dx}_{1}...

I read that most scientists believe that the Universe is either infinitely flat or pringle-shaped flat, and that doesn't make sense with me. I don't understand how our 3 dimensional world could be a part of a 2 dimensional universe.

Homework Statement Consider a flat FRW model whose metric is (in polar coordinates) ds^{2} = -dt^{2} + a^{2}(t)[dr^{2} + r^{2}d\theta ^{2} + r^{2}sin^{2}\theta d\phi ^{2}] where a(t) is the scale factor. Show that, if a particle is shot from the origin at a time and with velocity t_{0},V_{0}...

Sorry quick question from the ignorant (of maths or physics) but what does it mean to say that the universe is flat? I assume this does not mean it only has two dimensions! I do understand that it means that it has neither negative nor positive curvature, but what exactly does it mean in...

I am studying topology. There I learn that the open sets given by the metric can be used to define a topology, e.g. the usual metric topology on R^n given by the Euclidean metric. Now I try to understand the topology of (flat) spacetime. Is there a metric? The Lorentz 'metric' gives...

Could someone clarify, and/or point me to some reference on: Lorentz metric is not really a metric in the sense of metric spaces of a topology course since it admits negative values. If I use it to define the usual open sphere about a point, that sphere includes the entire light-cone through...

[SIZE="2"]I have plotted a lift curve of a NACA 643-418 airfoil section which has a flat region in the lift curve approximately from 11 degrees to 16 degrees. Beyond 16 degrees it completely stalls. Can some explain to me the reason behind this flat region in the lift curve. The experiment...

Am i right in saying that consenses amongst the cosmological community is that the curvature of space is 0? So it is flat euclidean geometric space (I hope I am using correct terminology) which is neither +/- in curvature but exactly 0? Am I also right in saying that flat cosmological models...

soo as the title says, i need formula for force acting on a plate that is moving trough fluid, in my case air... need it for rocket simulation because of its flat stabilizers... i thought like this: a flat plate is moving in any direction (yeah that complicates things... but keep it...

So if you take a sphere with coordinates (r, \theta,\phi) and keep \theta constant you get a cone. The geodesic equations reduce to (by virtue of the euler - lagrange equations): \frac{\mathrm{d} ^{2}r}{\mathrm{d} s^{2}} - r\omega ^{2}\frac{\mathrm{d} \phi }{\mathrm{d} s} = 0 where \omega =...

proving that the sphere cannot be expressed in "flat coordinates" for the sphere in R^3 i have that ds^2 = dϕ^2 + sin^2(ϕ)dθ^2. using the definition of a flat space as one where given a set of curvilinear coordinates, one can find a metric such that ds^2 = dx^2 + dy^2, how would one prove that...

Homework Statement Could anyone show me how I would go about finding all the killing vector fields for: ds^{2} = dx^{2} + dy^{2} + dz^{2} Homework Equations Requirement for a killing field: \nabla_{b}X_{a} + \nabla_{a}X_{b} = 0 (Sorry the indexes should be lower indexes but latex is messing...

Homework Statement Explain the factors that determine the parallel and normal components of the elctric field near to the surface of a flat metal plate Homework Equations The Attempt at a Solution No idea what this question wants..? Is it something to do with the smoothness of...

I am attempting to compute the integral of a function that is mostly flat relative to a few localized peaks. These peaks are the bulk of the contribution to the integral. I decided to try the VEGAS algorithm to do this. I am running into some difficulty, so I am reaching out to YOU...

Does anybody have any experimental data on flat back airfoils. I would like to know the experimental data, experimental setup and initial flow parameters etc. In case if you find it from a report I would be glad if you can give some information regarding the report, such as author, report name...

Why are solar systems and galaxies flat? I find it peculiar that astronomical clusters (ie: solar systems and galaxies) are arranged in a flat plane. Can someone explain why? I understand that: any solar system originates from a random cloud of dust and gas. This cloud will feel its mutual...

Hi, I have read Lift-it catalogue and I found out it is very professional and useful . I have some questions in the subject and I'll be grateful for professional answers. I found out that there is a direct relationship between SWL and the width of the strip (1600 lbs/in of width for nylon...

How is the force to move an object on a flat service calculated? Does it mater if it's flat or on edge?

Hi all, I have question regarding to heater I want to build. It suppose to be a heater used for soldering a thin copper sheet (1mm thick) with other small copper components. Heater has to be flat as much as possible and reach the temp up to ~250C (solder melting point). The copper sheet...

Hi, Killing equation in flat space is just \partial_{\mu}K_{\nu}+\partial_{\nu}K_{\mu}=0 . I've seen in various places the solutions to this written as K^{\mu}=\Lambda^{\mu}_{\nu}x^{\nu}+P^{\mu} where P is a constant 4 vector, and \Lambda_{(\mu\nu)}=0 (i.e. symmetric part vanishes and it is...

..that went an infinite distance in all directions: What would it look like? Would you technically be able to see all (or a lot) of it? (speed of light permitting) It's just a question that has been bugging me for a while.

Homework Statement Hey guys, I was just wondering how do the beliefs of the Flat Earth Society defy against modern day physics? I'm doing a discussion board post for my physics class. I know they strictly do not believe in gravity but what else do they do against? For example about Newton's...

Hey there I'm wondering why it's remarkably more exhausting to ride a bike with a flat tire, compared to a bike with a hard inflated tire. The friction force "killing my efforts" so to speak, should be the same; the normal force is the same (my mass doesn't change), and the friction...

Hello, I read that when a manifold has a flat metric, the geodesics are always straight lines in the parameter space. I have two questions: (1) If we are given a Clifford torus S^1 \times S^1 (which is flat), how do we compute the geodesic between two points? Is the following correct...

Homework Statement In a Young's double slit-type experiment using light of 600 nm with 0.5 mm between fringes, a thin plate of glass (d = 100 micrometers, n =1.5) is placed over one of the slits. What is the lateral fringe displacement on the screen? 2. The attempt at a solution To be...

In another thread, https://www.physicsforums.com/showpost.php?p=2973770&postcount=45, some questions came up about what the conditions are for a spacetime to admit flat spatial slices, and for a spacetime to have a time-independent "scale factor" (see definition below). These questions...