Spacetime Definition and 1000 Threads

...why do people like Stephen Hawking talk about things/events "before" the Big Bang? If time (as part of spacetime) was created with this event, it also marks the point in time that had no "before", doesn't it?

Are there any theories in physics that allow for a time component of the various vector quantities besides the x,y,z components? For example the velocity of a particle to have a time component ##v_t## besides the x,y,z components ##v_x,v_y,v_z##

Some models of gravity, inspired by the main theme of spacetime fabric of Classical GR, treat the metric of the manifold and the connection as independent entities. I want to study this theory further but I am unable to find any paper on this, on ariXiv atleast. I will be very thankful if...

If the Milky Way's halo is displaced supersolid dark matter, and the state of displacement of the supersolid dark matter is referred to geometrically as curved space-time, then is the Milky Way's halo the physical manifestation of curved space-time?

These two ideas seem to be categorically opposed. The concept of an event as a point in spacetime seems to not square with uncertainty and the concept of quantum intrinsic randomness seems to not square with unchanging spacetime... Assuming it is unnecessary to explain further why this is a...

If a black hole that is feeding is actually ingesting the spacetime around it (and hence whatever may lie in that spacetime including light) what does it do when it is not ingesting but nonetheless has very strong gravitational attraction? Does it sit there dragging empty spacetime into it? If...

If I understand spacetime correctly, if you max out the "space" component (travel as fast as possible), you will travel at the speed of light (speed of causality) and time will stop (or nearly stop) advancing for you.. but what if stopped completely? so you stayed stationary in the exact x y z...

The way I understand this is that Relativity says space-time is like a field that's affected by the way mass moves through it. Photons are massless so is this why the speed of light is the same in all reference frames?

The question is in the title. Nothing more to add.

If dark matter is a supersolid that fills 'empty' space and is displaced by visible matter, then is this the same notion as the spacetime fabric having mass and being curved by visible matter?

Imagining that an object spining around a spherical mass M has angular momentum that has z-component(θ=0) only, then $$g_{μν}\frac{dx^μ}{dτ}\frac{dx^ν}{dτ}=(1-\frac{r_s}{r})c^2(\frac{dt}{dτ})^2-\frac{1}{1-\frac{r_s}{r}}(\frac{dr}{dτ})^2-r^2(\frac{dθ}{dτ})^2-r^2\sin^2θ(\frac{dφ}{dτ})^2=c^2$$...

The other day I was pondering what happens at/near absolute zero so I did some googling and found articles talking about how it has been demonstrate that as you near absolute zero, the quantum effect start to have an increased range. However, is seems that perhaps the quantum effects only get...

Recently I found an experiment done by Prof. Sila Beane. In this experiment he simulates a tiny porportion of the universe using a QCD Lattice where spacetime is a discrete lattice. He inputs the GZK cutoff point of a cosmic ray into the lattice and what happens is, the result is that the...

Hi, my classmate asks me an interesting question: For a finite 4D volume in spacetime, its boundary is a 3D close surface. If the 4D volume is a 4D rectangular, the boundary consists of eight 3D surfaces. The boundary condition is specified on these eight 3D surface. Please explain the physical...

Homework Statement https://i.imgur.com/sI3JiB4.jpg https://i.imgur.com/PLpnPZw.jpg I have no idea how to solve the first question about the vacuum energy. I solved the second and third problems, but I'm hopelessly stuck at the first. 2. Homework Equations The Hamiltonian can be written as...

If a gravitational wave passes an elastic body it will be deformed. The source of the work done on it comes from the energy of the gravitational wave. In curved spacetime e.g. an accelerated expanding FRW- or static Schwarzschild-spacetime an elastic body will be deformed too. What is the...

I read the Special Theory of Relativity in Jackson's textbook, Classical Electrodynamics 3rd edition. Consider the wave front reaches a point ##(x,y,z)## in the frame ##K## at a time t given by the equation, $$c^{2}t^{2}-(x^{2}+y^{2}+z^{2})=0 --- (1)$$ Similarly, in the frame ##K^{'}## the wave...

Hi, I have a question about the bending of spacetime and its proportion and relation to the mass which causes the bending; and also how the bent space would interact with other objects as they come closer. I'm going to ask a more detailed question with some possible problems I would like to...

If what we perceive as the force of gravity is really just the effect of curvature of spacetime, why do theorists hypothesize the graviton as the force carrier for gravity? I thought that GR does away with the notion that gravity is a "force." So, is gravity a force or is it merely an effect?

I am trying to explain to someone why there is still gravitational time dilation at the centre of the Earth. (Not to over-tax the rubber sheet analogy, but...) When we sketch a gravity well, we show a curve that starts out nearly flat, then curves away from the flat plane, until it reaches the...

[Moderator's note: This thread is spun off from another thread since it was dealing with a more technical point that is out of scope for the previous thread. The quote that starts this post is from the previous thread.] I feel the same about transformations of Dirac matrices and Dirac field...

Let's say you can bend a paper...how about bending it upward. a slope I'm saying as we saw spactime in 3d...we all know how it looks..the lines are attracted toward Earth but why doesn't it deflects them and maybe negative mass is linked with it. In other words, someone under the trampoline...

I'm looking for a simple explanation or decent analogy whereby something that is symmetrical and smooth like a black hole or even a spinning neutron star can drag spacetime as if spacetime was a viscous liquid. It guess it might make sense to me if gravity was unified with EM. I can see how two...

Regarding curvature of spacetime/space: At some given point in a gravitational field, spacetime is curved at that point and this is a constant. (I'm assuming this is true). Although we can talk about the curvature of spacetime, I never hear anyone talking about the curvature of space. Can...

I'm very new to this site and most assuredly and not a physicist (or a scientist) , but I have a question I'm hoping y'all can help me with. If I were traveling at or near the speed of light for a set distance- say Andromeda and back, time will slow down for me relative to the static observer...

I started this post on physics.stackexchange but it's too vague for that site, so here I am! :) I'm trying to really get the intuition of spacetime. This video explains how Minkoswki was the first to think that maybe our universe does not consist of a 3d space which evolves in time, but rather...

Greg Bernhardt submitted a new PF Insights post This article is part of our student writer series. The writer Arman777, is an undergraduate physics student at METU A Journey Into the Cosmos - FLRW Metric and The Friedmann Equation Continue reading the Original PF Insights Post.

Hello, I've been wondering about this... If something like the Alcubierre drive is possible, that bends spacetime around it in order to reach great distances faster, why would this not affect other matter in its vicinity? If I'm understanding correctly, in order to move faster than light, a big...

I have some questions and refer you to the image below the caption of which states, "D-branes may be of exceptional importance in the explanation of elementary particles of the Standard Model. However, it still remains to find a solid connection between the M-theory and the Standard Model."...

I am unable to find any paper or book on Kerr-Bolt solution. I need to know its derivation. Please if anyone can suggest some material on it? I will be very thankful.

Greg Bernhardt submitted a new PF Insights post The Schwarzschild Metric: Part 1, GPS Satellites Continue reading the Original PF Insights Post.

Let us say, that we have a curved spacetime, for instance, Schwarzschild metric. Can it be embedded in five dimensional noncurved Lorentzian spacetime, or we need six dimensional Lorentzian spacetime with two time dimensions? Books only write that it is not necessary that this space is...

Hello physics forum. I am not very well versed in physics, so this question could be a misfire, but I just wanted to clear this up. I watched one of Susskinds holographic principle lectures. So I get that Bob would see Alice turn into a hot mush of energy as she approaches an event horizon...

I know this is probably going to sound stupid but I'm really curious for the opinion of someone who has knowledge. Well spacetime is like a stretched bed linen. Putting on an object with a big mass, will cause its curvature. Now imagine having a piece of fabric holding it stretced from both...

If space time (the universe) is infinitely expanding what happens when it rips? Have we observed Virtual particles in an area and counted them? Does the expansion of space time affect the amount of Virtual particles in a particular area? Is it theoretically possible to expand space time to a...

I still have some confusion of the concept of spacetime as geometry. Specifically, what confuses me is causality related to this geometry. My understanding is that stress-energy of matter/energy curves spacetime, the curvature of spacetime tells matter/energy how to move, and dictates to...

bosonic string theory requires 26 dimensions superstring theory requires 10, 9 spatial 1 dimension of time Witten has researched twistor string theory has there been any serious research with (super) string theory written on 4 complex -valued dimensions of spacetime? the additional dimensions...

Dirac's rest mass seems to be expressed as a fourth dimension. If we were to try to include this rest-mass dimension into Minowski space time, could it be expressed as a distance in space? S^2=x^2+y^2+z^2+(rest-mass dimension)^2-(ct)^2?

thus far the LHC hasn't found any evidence of SUSY or technicolor. thus far it's just 1 fundamental scalar there is an extensive literature on the Higgs hierarchy problem with various proposals and solutions offered has there been any scientific papers and research on the physical properties...

So General Relativity explains the force of gravity as mass/energy induced curvature of spacetime. This correctly predicts gravitational time distortion, nonlinear geodesics and gravitational lensing, the anomalous precession of planetary orbits, the schwarzchild metric, and so on. Could the...

how does scientists discover the spacetime ripples and this things while the spacetime is not a real fabric is this all returns to the LIGO lab and the machine that was built there ?

The article https://en.wikipedia.org/wiki/Malament%E2%80%93Hogarth_spacetime, the possibility of a space with a "worldline λ and an event p such that all events along λ are a finite interval in the past of p, but the proper time along λ is infinite" is discussed, and the suggestion is made that...

Greg Bernhardt submitted a new PF Insights post Mathematical Quantum Field Theory - Spacetime Continue reading the Original PF Insights Post.

Regarding Einstein's static universe John Baez explains in The Meaning of Einstein's Equation To see this, consider a small ball of test particles, initially at rest relative to each other, that is moving with respect to the matter in the universe. In the 13 local rest frame of such a ball, the...

Can someone tell me how we know that our physical universe is geodesically complete? In response to a question I had about why we assign any meaning to the other side of a black hole’s event horizon (or its interior), I got an answer prompting me to look into the concept of geodesic...

Hi guys, I'm not exactly sure how to go about doing this problem. The question has no additional information, so I'm stuck. Any help I could get would be appreciated. 1. Homework Statement In four dimensional Minkowski spacetime an event, A, has components labelled Aμ and another event B has...

Hi guys, Do virtual particles, when they are fermions, obey Pauli exclusion principle as real fermions do? More specifically, what I am wondering is the following: Fermion fields would have some energy at every point in spacetime due to the uncertainty principle. Now, is it possible for the...

Consider a non-radial timelike geodesic outside the event horizon. Will it nevertheless cross the horizon radially or are non-radial geodesics also possible inside? I couldn't find any reference regarding a possible angle dependence in this respect.

When you do a Fourier transform of spacetime.. what do you get? (or how does spacetime look in frequency domain? And what applications do this and what results are they looking or solving for?

If you search for "does a photon experience time", almost every other link says that they travel at the speed of light and so STR tells us that its clock doesn't tick at all. However why do they use the arguments for special relativity which was developed for massive particles moving close to...