Recent content by Keys

Well, I'm back thinking about this. Looks like the example I gave in post #4 is not 22.5 degrees. Just to check for display problems I did a 2nd mirror image and then rotated it until it aligned with the other and it seems that the new major axis is around 19.5 degrees from horz, not 22.5 so...

I'm starting to think I'm only questioning this because I am trusting the software plot on my screen too much. For example I'd start with a circle and transform it 2x on the horizontal, then take the resulting ellipse and transform it 2x again along 45 degrees from horz, I was expecting the new...

Thx for the reply Tiny-tim, but I don't think the way you're looking at it fits the problem I described because in your explanation the ellipse's minor axis can never be larger than the diameter of the cylinder, no matter how many arbitrary rotations you give the plane. In the problem I was...

If I stretch an ellipse with .5 eccentricity along an axis 45 degrees from its major axis, doubling its area. How do I find the angle of the major axis of the resulting ellipse? Is there a simple rule based on the amount you stretch and the angle and orig eccentricity? Thanks.

Sorry to revive such an old thread but I have never heard of gravitational potential not equaling the gravitational field in GR. It seems that the same subject was covered in an even older thread: https://www.physicsforums.com/showthread.php?t=40391" It seems to me that Pervect would argue...

I guess you've never noticed all this talk of branes or membranes.

Thanks Mathman for your answer. I'm a bit dense, does this parametric form work even higher dimensions? Let's say the last example 2 planes in a 4 space, could be considered 2 different 2 spaces both within a 4 space. By my reasoning a 3 space and 2 space that are both within a 5 space where...

If we look at 2 intersecting orthogonal planes in 3D, the intersection forms a line if you are "living" on either plane. How would the intersection look if there are 2D planes in 4D where the planes do not share a dimension? For example plane 1 exists on X and Y, and plane 2 exists on Z and T...

I've thought of such a device in high school, the problem is finding a 100% reflective material. The construction is not a problem if you abandon these closed sphere or box ideas. All you need is 2 parabolic mirrors of different sizes. Position the mirrors facing each other so that the foci are...

OK, if they look the same, then they are considered equivalent? What's the point in specifying then? This leads to my 2nd question, if a one loop open string is attached to a d-brane, I've read it cannot be detached. But if we can just relabel it a tree closed string, then it is detachable? Thanks.

Can someone please explain to me why string theories with open strings must also have closed strings? I've read it is due to conservation of energy, an open string not attached to a closed string will lose it's energy off an end. Does this mean all D-branes must be made from closed strings? I...

From the photon's point of view the travel time doesn't exist. It is emitted then the next instant it is absorbed. Even if it needs to travels to another galaxy, from it's perspective it takes the same time as going an inch, which is no time at all.

You'd probably get more response in the quantum mechanics section. But I'd watch the Feynman videos found here http://vega.org.uk/video/subseries/8" for a clear explanation. Or check out Feynman's easy to read QED.