# What is Lorentzian: Definition and 38 Discussions

In differential geometry, a pseudo-Riemannian manifold, also called a semi-Riemannian manifold, is a differentiable manifold with a metric tensor that is everywhere nondegenerate. This is a generalization of a Riemannian manifold in which the requirement of positive-definiteness is relaxed.
Every tangent space of a pseudo-Riemannian manifold is a pseudo-Euclidean vector space.
A special case used in general relativity is a four-dimensional Lorentzian manifold for modeling spacetime, where tangent vectors can be classified as timelike, null, and spacelike.

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1. ### Lorentzian line profile of emitted radiation

First of all i tried to follow the textbook. Here they start of by modelling the atom as an harmonic oscilator: Then they find the solution as: They neglect the second term as omega_0 >> gamma which also makes good sense so they end up with: So far so good. After this they state the...
2. ### Python How to properly normalize convolution of Gaussian and Lorentzian

I'd like to plot the normalized convolution of a Gaussian with a Lorentzian (see the definitions in terms of full width half maximum (fwhm) in the attached image). Here is my attempt, but the print statements with np.trapz() do not return 1 in both cases, but rather ##\approx##0.2. I'd also like...

7. ### I Lorentzian line shape integration

Hi, I know this might be a bit dum but I'm currently stuck with this integral. In this link: http://www.pci.tu-bs.de/aggericke/PC4e/Kap_III/Linienbreite.htm I know he's doing the right thing, but I really don't understand the integral of a(omega). How come it is E(1/(i(ω-ω0) -γ) -...
8. ### I Definition of a Lorentzian Wormhole

I was reading into traversable wormholes when I came across this definition from Matt Visser; 'If aMinkowski spacetimecontains a compact region Ω, and if the topology of Ω is of the form Ω ~ R × Σ, where Σ is a three-manifold of the nontrivial topology, whose boundary has topology of the form ∂Σ...
9. ### Two dimensional Lorentzian vs Euclidean geometry

Reading a somewhat long and argumentative thread here inspired the following unrelated question in my mind: Where does a 2 dimensional flat Lorentzian geometry depart from Euclidean geometry as axiomatized by Euclid? I.e. Euclid's axioms (in modern language) can be taken to be: We can...
10. ### Find Lorentzian Scalar Product on 4-D Lie Algebra G

Hi everybody, Let G a four dimmensionnal Lie group with g as lie algebra. Let T1 ... T4 the four generator. I would like to find à lorentzian scalar product (1-3 Signature) on it and left invariant. A classical algebra take tr (AB^t) as scalar product but I don't find à lorentzian équivalent...
11. ### Time-orientability of Lorentzian manifolds

A spacetime is said to be time-orientable if a continuous designation of which timelike vectors are to be future/past-directed at each of its points and from point to point over the entire manifold. [Ref. Hawking and Israel (1979) page 225] I want to make sure what conditions must hold in...
12. ### Understanding Conformal Time & Lorentzian Manifolds: A Layman's Guide

Can anyone give a laymans explanation of conformal time in relativity? I tried to read Roger Penrose's book but I found it hard to grasp.Thanks in advance . Also is a Lorentzian manifold different to a conformal manifold? A laymans explanation would also be much apprecitaed.
13. ### Are all solutions to Einstein's Field Equations Lorentzian manifolds?

From the things I've studied till now, the thought came into my mind that all of the known solutions of Einstein's Field Equations are Lorentzian. Is it correct? And if it is correct, is there something in EFEs that implies all solutions to it should be Lorentzian? And the last question, do more...
14. ### Why never any length expansion under Lorentzian Relativity?

Lorentz believed in the ether, and developed his version of Relativity Theory based on interactions of moving charged particles (electrons, specifically) with the ether. What I don't understand is how one always gets length contraction for movement in an inertial system moving with respect to...
15. ### Classical and Lorentzian transformation for doppler effect

Hi everyone, I am having some problems understanding Bergmann's problems. Problem 3 from Chapter 4 from Intro to the Theory of Relativity by Bergmann 1. Suppose that the frequency at a light ray is f with respect to a frame of reference S. Its frequency f′ in another frame of reference, S'...
16. ### How time starts in LQG with onset of Lorentzian phase

In the recent analysis by Mielczarek, Linsefors, and Barrau, the key parameter is ρc the highest density achieved in the bounce. The extremes (negative and then positive) of the Hubble rate occur symmetrically at density ρc/2 In the contraction preceding bounce, as the density approaches ρc/2...
17. ### Can We Define Angles in Flat Spacetime Using Geodesics?

In another thread, it was asked if we could use the angular deficit idea to determine curvature not in space, but in space-time. My idea to attempt to proceed along these lines would be to generalize the idea of angle, but I don't have anything that I feel I can point to. As a starting...
18. ### Physics Lab, Transient response of LCR circuit, lorentzian curve

I wasn't exactly paying much attention during our lab, partially because it was right in the middle of midterms and I wanted to solely focus on those. Now it is coming back to bite me as I am not entirely sure how to complete my lab report, or the theory behind the lab really. If you would like...
19. ### Lorentzian 2-Manifold Local Conformal Flatness: Explained

I have seen it stated that any Lorentzian 2-manifold is locally conformally flat; in what sense is it local? Is there a way to show this explicitly?
20. ### Lorentzian Curve: Is It Normalized?

Is a lorentzian curve by definition normalized? As far as I can tell it is such that ∫L(x) = 1.
21. ### Lorentzian line shape function

Hi I have a problem where the flux of a particle beam is measured using a (nearly) perpendicular laser beam and a photomultiplier. I have a function looking like this: L(\nu) = \frac{\gamma/2}{(\nu - \nu_0 + kv)^2 +(\gamma^2/4)} I suppose this is a Lorentzian lineshape function...
22. ### Fourier transform of a lorentzian function

hi I know the Fourier transform of a lorentzian function is a lorentzian but i was wondering if the Fourier transform of the second derivation of a lorentzian function is also a second derivative of a lorentzian function Thanks
23. ### How Does Velocity Factor Influence Lorentzian Line Shape Profiles?

Hi I hope some one can help me with this one: I have a Lorentzian line profile L(√L) = 1 / ((√L - √0 )^2 + (\Gamma2/4)) for v = 0. For v \neq 0 I have \int(1 / ((√L - √0 - kvz)^2 + (\Gamma2/4)) * g(vz) dvz) I suppose the factor g(vz) dvz is a velocity factor, but how do I...
24. ### Mathematica Mathematica: Convolution between Lorentzian and Gaussian

Hi I have the following code: lorentz[A_, Ox_, Oy_, FWHM_, x_] := A (1/3.14) FWHM/((x - Ox)^2 + FWHM^2) + Oy; gauss[A_, Ox_, Oy_, x_, C_] := A Exp[-(x - Ox)^2 C] + Oy; Convolve[lorentz[1, 0, 0, 1, x], gauss[1, 0, 0, x, 1], x, y] It takes extremely long time for this to finish -- is it...
25. ### Lorentzian contraction of a box increases the pressure inside?

Lorentzian contraction of a box increases the pressure inside? I have been doing some research on gravity, and I am having a very hard time with the following example I found in a book entitled Gravity From the Ground Up by Bernard Schutz. It sounds like a 3rd grader explaining...
26. ### Prove the lorentzian function describes resonant behavior

Homework Statement Resonances occur in many physical systems, and are often observed by measuring the frequency response of the system to an applied driving force. use the example of a damped harmonic oscillator to show how the lorentzian function serves as a good description of resonant...
27. ### Is the vectorial representation of the Lorentzian Group unitary?

I am 99% sure it is not, but I would like to hear that from someone else to be more serene.
28. ### Get Lorentzian Spherically Symmetric Metric to Sylvester Form

Hi, I'm trying to determine the exact transformation that brings a spherically symmetric spacetime metric in spherical coordinates to the Sylvester normal form (that is, with just 1 or -1 on its main diagonal, with all other elements equal to zero.) Assuming that the metric has Lorentzian...
29. ### What is the Generalized Approach to Lorentzian Relativity?

Hendrik Lorentz, a Nobel Prize-winning physicist who was a mentor to Einstein, developed his own theory of relativity before Einstein. Einstein's theory uses the "Lorentz transformations" explicitly, but the interpretation of these formalisms is quite different in each theory. Einstein made...
30. ### Lorentzian spinfoam model free of IR divergence (Muxin Han)

http://arxiv.org/abs/1012.4216 4-dimensional Spin-foam Model with Quantum Lorentz Group Muxin Han 22 pages, 3 figures (Submitted on 19 Dec 2010) "We study the quantum group deformation of the Lorentzian EPRL spin-foam model. The construction uses the harmonic analysis on the quantum Lorentz...
31. ### Lorentzian lineshape, uncertainty principle and AlGaAs conduction band offset

Homework Statement 1) I try to understand the lorentzian lineshape and relate to the gaussian graph but i don't know what is the difference. 2) Uncertainty principle- if it's related to the lorentzian lineshape it will give the information about the lifetime in the well and the width of...
32. ### What is the FWHM of a Lorentzian distribution?

Homework Statement Hi If I have a Lorentzian distribution given by f(x) = \frac{\Gamma}{x^2+\Gamma^2}, then is Γ the FWHM?
33. ### Proving That a Lorentzian Structure Cannot be Put on S^2

It is fairly easy to prove that each manifold can be given a Riemannian structure. The argument is standard: locally you give the riemannian structure and then you use partions of unity. This proof breaks down for signed metrics. Even for a manifold requiring only two charts. For example, I've...
34. ### Is Lorentz Ether Theory a Viable Alternative to General Relativity?

H.E. Lorentz, a Nobel Prize-winning physicist, was an older contemporary of Einstein's who inspired and guided Einstein in his work. Lorentz, however, never fully subscribed to special or general relativity and believed to his death that what is now called "Lorentz Ether Theory" was the better...
35. ### Length contraction in Lorentzian relativity

Hi, I'm trying to understand Lorentzian relativity (Lorentz ether theory, whatever) which is empirically equivalent to the Einsteinian STR. I have, however, a problem in comprehending length contraction. In the Lorentz theory we have a preferred frame and length contraction is a real...
36. ### Visser: Lorentzian wormholes. From Einstein to Hawking 1996

Matt Visser - Lorentzian wormholes. From Einstein to Hawking (Springer) (1996) Just opened this book. Does anybody know it, and if you do, do you recommend it? Any feedback on this book.
37. ### Smooth deformation of a Lorentzian manifold and singularities

How can a smooth deformation of a Lorentzian manifold possibly create one or more singularities?
38. ### What Are the Differences Between Riemannian and Lorentzian Spin Networks?

Can someone tell me what's the difference between a Riemannian spin network and a Lorentzian spin network?