# Tagged Questions

As a consequence of the Lorentz transformations, time and space transform into each other when changing reference frame. This calls for a unified description: Minkowski spacetime.

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### Why does the thought experiment of a photon bouncing of a mirror imply anything for other objects?

Okay, so I am reading a book, "The Elegant Universe" by Brian Greene, which talks about motion and its effect on time. Greene makes the point that time changes with motion by saying that if you have ...
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### How can the universe by infinite when it has known start and finite time since? [duplicate]

Just watched the 'How Big is the Universe?' TV program and it indicated that the universe is believed to be infinite in size. They used an approach involving measuring the internal angles of triangles....
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### Is the Big Bang instant considered a beginning of all the coordinates of our universe? [duplicate]

Is the Big Bang instant considered a beginning of all the coordinates of our universe? If we consider the BB to be the Beginning of of our universe, can we call this the Origin of all of the 3 ...
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### What is Minkowski spacetime?

I was browsing through an article on spacetime when I caught the words Minkowski Spacetime. A Wikipedia search brought me an article too complex for me to totally understand. So what is Minkowski ...
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I have a physics question in a text sheet. I am currently doing work on relativity where calculations of rest frames and laboratory frames are being completed. The formula: $t(\text{laboratory frame}) ... 1answer 52 views ### Can invisible galaxies exist? [duplicate] Is it possible that there are newly formed galaxies which are moving so fast that we will can't see them, even though they exist "inside" our visible universe? I've been wondering if this could be a ... 2answers 404 views ### Why do things slow down when you move faster, rather than speed up? I've been trying to get to grips with SpaceTime. As I understand it, we move at a set rate through spacetime. Any increase in our rate of travel through space results in a decrease in our rate of ... 1answer 30 views ### Is the term “Lagrangian density” specific to spacetime? Wikipedia talks about Lagrangian densities here. But they never actually say whether they're just applying the concept to spacetime or that Lagrangian density is the analog for Lagrangians but for ... 1answer 72 views ### Is a black hole really a hole in space? [closed] What if when a supernova occurs, instead of it condensing into a singularity it creates enough force to tear a hole into the fabric of space? Is a black hole just what is sounds like, a hole in space? 1answer 324 views ### Are we living in a Universe with 3 time dimensions and 1 spatial dimension? [duplicate] If I said that we are living in a Universe with 3 time dimensions and 1 spatial dimension, would I be wrong? By that I mean if the spacetime interval was evaluated as ... 2answers 151 views ### Lorentz transformation paradox I got to solve a simple exercise about special relativity when I kinda came to the conclusion it doesn't stroke with my intuition. The homework-problem The problem was about two people Sam and ... 1answer 99 views ### Space-Time and Entropic gravity [closed] Gravity warps space-time, and Gravity can be thought of as Entropy. (Entropic gravity) So, as spacetime expands, how is space-time Entropy (or the inverse of gravity) effected? (If this is a noob ... 0answers 75 views ### With the new time cloak technology could it be possible to stop time for everything except one person So I was just reading up on some new research on national geographic from the Cornell University scientists and it seems that they've managed to bend waves of light around something to hide it from ... 2answers 3k views ### Why isn't the center of the galaxy “younger” than the outer parts? I understand that time is relative for all but as I understand it, time flows at a slower rate for objects that are either moving faster or objects that are near larger masses than for those that are ... 1answer 55 views ### Does the payload of an Alcubierre drive have to be on board during the preparation phase? I was thinking about the practical aspect of using an Alcubierre drive, assuming one existed. I'm no expert, but my understanding is that, since the destination has to be in the forward light-cone of ... 3answers 1k views ### How strong must gravity be to stretch time? I'm not sure if this is true or not but I heard that gravity has the ability to stretch time, and I was wandering if this is true. If so, how intense/powerful does the gravitational force have to be ... 1answer 118 views ### Empty Space - Could we exist without it? [closed] I have been giving empty space much thought. I imagined reaching the edge of the Universe and thought of 2 scenarios(focusing on 1): There is no more empty space 1.1 Would space extend with me if ... 5answers 105 views ### Does spacetime have a “preferred” speed/metric? [duplicate] I read recently that spacetime has a preferred speed, c, and that all observers would agree on the speed of anything moving at c. In particular, there is nothing unique about light when talking about ... 2answers 424 views ### Curvature gravity and a falling apple? [duplicate] I know very little of physics after Einstein. I am aware of that Einstein's gravity theory says that the existence of matters creates curvature of a space-time, so that our Earth orbits our Sun. I ... 4answers 261 views ### Is light amplitude spatial? In diagrams I often see light waves depicted as little sine waves that travel through space. And often when describing polarizers, the explainer will angle their hand to show the angle of ... 6answers 885 views ### Mass without Matter? My cursory studies of general relativity had introduced me to the concept of how gravity is associated with the warping of spacetime and that the presence of matter in space warps space and this ... 3answers 157 views ### How do we expect distance measurements to compare inside and outside the event horizon of a black hole? I've read that as one approaches the event horizon of a black hole, time is dilated relative to time measured farther away from the event horizon (clocks tick slower near the event horizon). I've ... 3answers 150 views ### Is a metric tensor field the same thing as$ds² = -dt² + dx²+ dy² + dz²$? I am having trouble understanding the nature of the metric tensor field on spacetime manifolds. In particular, a Riemannian manifold$(M,g)$is defined as a real smooth manifold$M$equipped with an ... 1answer 235 views ### Does a spacetime manifold have the structure of a metric space? My first introduction to spacetime physics was Wheeler and Taylor's book Spacetime Physics. This book gave me an appreciation for how important the spacetime interval was for giving the distortions to ... 1answer 153 views ### General relativity: is curvature of spacetime really required or just a convenient representation? I'm not really far into the general theory of relativity but already have an important question: are there formulations that can do without spacetime curvature and describe the general theory of ... 2answers 105 views ### Is a non-accelerating object far from a gravity source moving at the speed of light through time? I'm trying to understand the Minkowski spacetime better. If an object is not undergoing acceleration, and is far from any large mass, does it travel maximally "fast" through time? Can we calculate a '... 2answers 912 views ### Curvature of spacetime as a real thing? I get the curvature tensor in General Relativity, it is “just” math. Does space-time REALLY curves as a tangible thing, or is Einstein proposing a mathematical abstraction? More naively, please allow,... 2answers 1k views ### Spacetime geometry around two black holes For space-time geometry we all know images like he one below. But if I were to take a neutron star and put it right next to but not touching a black hole what effect would that have on the geometry of ... 1answer 53 views ### Expanding possibilities How does the nature of space-time and how we are able to interact within it relate to the expansion of space? If Space expansion ceased to be a constant would a body of mass still be able to change it'... 2answers 453 views ### Is space stretched with no limits by a black hole? Some depictions of black holes show space being warped into a singularity, with no end, e.g. as pictured below. Moreover, in Cosmos, Neil Tyson speculates with the possibility that Black Holes contain ... 2answers 140 views ### Is the surface of a heavy sphere bigger than$4 \pi r^2\$ due to general relativity?

I am unfortunately not familiar with the mathematics behind general relativity. However, on a heavy planet (say a sphere) gravity will bend space-time in a way that an object initially in rest, will ...