What is Flat: Definition and 495 Discussions

I just finished a problem from ryden's intro to cosmology, but I am not sure the answer makes sense here is the problem and my work: suppose you are in a flat, matter-only universe that has a Hubble constant H0=70 km/s Mpc. you abserve a galaxy with z=1. how long will you have to keep...

Can someone please tell me, the coordinate transformation that will make the following metric: ds^2=dr^2 + r^2d\theta^2 look locally flat? Many thanks.

I am required to analyze the physics for 4 scenes in the movie Top Gun. In one scene, Maverick's plane goes into a flat spin. Would it be possible for someone to explain this in from a physicist's point of view. Equations would be nice too lol. I am new to hpysics so please don't get mad lol...

It seems to me that people with flat feet should have been weeded out by evolution back in the day when they actually had to walk and run around all day long. Am I missing something? Aren't people with flat feet at a huge disadvantage in those conditions?

Do the matter and radiation of a flat universe, as time approaches infinity, conform to a spherical shell?

This is a bit of a lark, but I'm just wondering if I've understood correctly to draw my conclusion... It is my understanding that the curvature of spacetime postulated by GR is what causes orbits which appear elliptical. An orbiting body is following its inertial path which might otherwise...

How much net work is being done when a car is traveling at a constant speed on a flat road? I think there is not net work done. :bugeye:

Ok i can stand on a flat roof with some sort of wall or at least waist high railing around it, but i could not even think of standing on one without either, not even in the middle, crazy or what?

hello. I know when omega is equal to, less than or greater than one our universe is either flat open or closed respectively. omega is the ratio of the current observed density to critical denisty in the universe. my question is that we can only see our part of the universe (that is 13...

Hey guys, so I'm back in school after an 8-month break, and I'm feeling a bit rusty :rolleyes: So I've got a flat disc of radius A, with constant density p, in the z=0 plane. I want to calculate the gravitational field at any point up or down the z-axis. I integrated the potential over the...

Does anyone know where I can get a few 10-pin female flat ribbon cables. They look like this: http://hubbard.engr.scu.edu/embedded/lcd/lfh8p4032b/P1010029.JPG The header looks like this: [ooooo] [ooooo]

I have read from Universe by Freedman, Kaufmann that our universe is largly flat so it would mean there are edges in our universe. Our universe would be like a flat piece of paper that is continually expanding. A more realistic picture might be a diagram of Einstien's fabric of space time which...

I'm reading Parallel Worlds by Michio Kaku and I keep wondering if space is flat, then what would happen if you kept moving directly downward under our solar system (or directly down from any other planet)? What would you see and where would space end or simply curve back around. Thanks!

I realize this may be a really obvious question, but wikipedia and google haven't help settle my curiousity. If the universe is in fact a flat universe, as I believe has been proven with experimentation, this, if I am not mistaken, means the universe will continue to expand to a limit without...

We know if the Earth is considered flat the maximum range is obtained when the missile is launched at an angle of 45 degrees. But what if we take into account the curvature of the earth? what is the maximum arc-length of the range? :confused: Thank you!

We know if the Earth is considered flat the maximum range is obtained when the missile is launched at an angle of 45 degrees. But what if we take into account the curvature of the earth? what is the maximum arc-length of the range?:confused: Thank you!

For a beginner (as I am since a long time), it is convenient to conceptualize curved spaces as embedded within a familar flat space with more dimensions. Of course the intrinsic point of view is more elegant and suffice to itself. Nevertheles, I am asking this question: are there some curved...

If the emissivity of a flat surface varies with zenith angle according to e=E*cos(theta) where E is the emissivity at zenith. Would this surface radiate isotropically? I think that because the emissivity varies then the emitted radiation varies accordingly so the energy measured from...

Why are the bottoms of large clouds flat?

So why exactly does the military refuse you if you have flat feet? My friend is trying to join the US Marines but they refused him because he has flat feet. Does this make you unable to do something required of a soldier or what?

If you have ever seen a tall chimney fall, you will have observed that they break up on the way down. This is because of the effect you have found. What is even more interesting a cylinder falling in that manner will break into 3 large pieces and some crumbs (about .14 ) so the chimney...

hi, for most of you this might be a simple question: Is it possible to embed the flat torus in Euclidean space? If we, for example, take a rectangle and identify the left and the right sides we get a cylinder shell, that can be embedded easily in R^3. If we construct the...

I had a flat last week. Today I just went and got the spare fixed, so I'll be ready for the next flat. I get about two flats a year. That seems high compared to most people I know. The reason I have so many is that most of then come from driving my pickup to the landfill where there are always...

and does not slide off. in this case does centripetal force = frictional force? I think the answer is yes, but want to make sure. thanks

I am a trying to work out a design issue that you may be able to help with or maybe point me in the right direction. I am designing a 17-4 stainless steel plate to be used to support a trust bearing. The dimensions are 3.333 inches in diameter with a 1.20 inch center bore and .097 inches...

U. S. corporations paid 60% of the budget 50 years ago compared to 16% today. Would a flat tax introduce a more fair distribution? (Another example of corporate rights overtaking individual rights.)

Is it possible to get a near perfect flat surface with the roughness no more than 1-10 nm at any point? If it is, then how difficult is it?

what does it mean for the universe to be "flat"? What is the difference if the universe was flat or curved at all?

determine the minimum height of a vertical flat mirror in which a person 5'0'' in height can see his or her full image. I have absolutely no idea how to solve this type of problem... Since we don't know the distance between the object and the mirror, how in the world can we calculate the...

Inside a shell of matter I would experience a flat gravitational potential and hence no gravitational force. Is there any experiment I can do, short of leaving the shell, that could allow me to determine the existence of the potential? For example would my extra potential energy show up...

Have I got it right this time? Red-shifting is determined by the difference between the space-time curvature at the light source and the observer's space-time curvature. For the light source, all that matters is the distance from the center of gravity -- I think the motion of the source...

Closed spacetime with its dispersed masses and open spacetime under dark energy interfere dynamically at the Euclidean boundary. This zero curvature surface distinguishes where the cosmic geometry contracts from where it expands, and represents a significant unexplored structure within familiar...

My first post here, this question may have been asked before and answered already, if so a link would be appreciated. When we measure interstella distances are we measuring curved space distances or flat space distances? Putting it another way... Are we able to determine the curvature...

Studies of black hole physics by people like Hawking and Bekenstein suggests that our perceptual universe, which is perceived to have three spatial dimensions, might instead be "written" on a two-dimensional surface, analogously to a computer generated holographic projection. The everyday...

Just wondering what the general scientific community thinks about this topic.

We're doing a project for my engineering tech class, and i need to conduct a survey, we'd be really obliged if u could answer the survey questions. 1. When thinking about bridges, what is the first bridge that to your mind? 2. Why? 3. If crossing a bridge, do you look over the edge? 4...

Hi, I'm working on a kinematics problem of rolling a golf ball on a flat plane (4-position infinitesimally separated solution). The solution sought is to be planar, so we're working in 2D only. This is largely irrelevant though, as I'm facing a rather undergraduate puzzler. I need to...

The question is : A car travel in a flat circle of radius R. At a certain instant the velocity of the car is 18 m/s west and the total acceleration of the car is 2 m/s2 at 46 degrees north of west. What is R? I simply used a = v2/R and obtained 162 m. I suspected the question should be...

A car traveling on a flat circular track accelerates uniformly from rest with a tangential acceleration of 1.7m/s^2. The car makes it one quarter of a way around the circle before it skids off the track, Determine the coeficient of static friction between the car and track? I really have no...

Very interesting.

What exactly is the problem with a flat, finite universe? I've often heard it quoted that a flat universe must be infinite... but it's easy enough to design space-times that are perfectly flat yet are bounded. For example, S^1*S^1*S^1. What additional information is used to suggest a flat...

in this link Dr paul marmet states----- the universe is flat there is no space contraction there is no time dilation. http://www.Newtonphysics.on.ca/faq/flat-universe.html confirmation of non time dilation...

Just stumbled on the fact that Russia adopted a flat tax system about two years ago. Productivity rose rapidly afterwards and now at 10% growth per year. I reviewed Dick Armey's proposal wherein he uses a flat rate of 17% for all tax payers, but includes savings for being married, number of...

Most of the matter in our solar system lies roughly in a plane. I always wondered why. I imagine that there is a well understood reason for this, but I never came across it. I came up with this: Assume we have a large star nearing nova. It spins rapidly, and has a large magnetic field...

As far as I am aware scientists agree that the universe is flat, open or closed. However, if galaxies get further away from each other the gravitational attraction between them would decrease as the universe expands. Why is the universe speeding up not a real possibility?