Relativity

FAQ article development, feel free to ask questions or make suggestions. (I'm still working on the Einstein field equation section. Probably keep that portion seperate to minimize length) This question is amongst one of the most commonly asked questions in relativity. Numerous articles both in pop media and peer reviewed articles refer to terms such as space time fabric, space time curvature. This leads the new learners with a common misconception that space has some mysterious fabric or material like property. To answer this properly we need to describe a few principles. A) gravity influences mass B) energy is a property of particles, or physical configura…

During this grueling time of self quarantining I've been trying to practice a little mental gymnastics everyday and I think I've come up with a small paradox. Well for me anyway. Let's say we have two stars 10 light years apart, star A and B, you have a space ship with 'magical technology" that allows you travel 5 light years in an instant. So you get in your space ship at Star A instantly you are 5 LYs from both stars, I'll call that point C, looking back at star A you see light that is 5 years in star A's past but the light from star B is 5 years in star A's future. The reverse would also be true. Star B's light you see is 5 years in star B's past but still in 5 y…

Some day in the far, far future mankind will travel the stars; this is inevitable, it is in our genes. Believing this I have been contemplating how we get to where we want to go. I do not believe we can carry enough fuel to propel us, nor do I believe we could find the fuel we need along the way. Having said that the only choice we have is to use another source of energy that we have not considered before. That source of energy gravity. Gravity has an almost limitless power; it holds planets in orbit around our sun and solar systems together. I believe we need to find a way to use the pulling force of gravity to pull us in the direction we want to go. We lock on…

Usually when I have these long trains of thought, I've gone off the rails early and rest is nonsense. Hopefully this all makes sense, but I at least hope someone can put me back on the rails so I can try again. The precursor to all this was thinking about the twin paradox. I get it - sort of. I believe the math works out, and I believe that there isn't really a paradox. But I feel like I'm watching shadows - I get the general idea, but I can't see the finer details. I don't like the explanation that one twin was in a single inertial frame and the other went through multiple frames. Why would that be a given? Why can't it be the other twin that stayed in …

A ten meter ship travels as close to light speed as to have all the universe compressed to 1 m length, in the direction of the movement. As the ship remains stopped for the pilot, its length remains ten meters for him. If the universe is 1 m in length, where is the ship flying?

I was prompted to start this subject by an article I came across, as follows..... https://www.sciencealert.com/scient...-drives-seriously-especially-this-one-concept Scientists Are Starting to Take Warp Drives Seriously, Especially This One Concept: MATT WILLIAMS, UNIVERSE TODAY 1 MAR 2020 It's hard living in a relativistic Universe, where even the nearest stars are so far away and the speed of light is absolute. It is little wonder then why science fiction franchises routinely employ FTL (Faster-than-Light) as a plot device. However, in recent years, the scientific community has become understandably excited and skeptical about claims that a parti…

I have some problems/questions regarding the existence of black holes. First, here is the current state-of-affairs in the physics community AFAIK: Black holes "exist" in the sense that they are physical objects in the Universe Black holes contain an event horizon, located at the Schwarzschild radius, beyond which "nothing can escape" Black holes are likely located at the center of many galaxies, including our own; "micro black holes" are also likely formed and quickly evaporate in our atmosphere due to relativistic cosmic rays Quantum mechanics is anticipated to resolve any mathematical singularity issues at the center of black holes There …

In physics when we say two events occurred simultaneously at two locations--is that synonymous with saying they coexisted at those two locations? When we say the words “coterminous events”, it is taken for granted that we mean the two events coexist at a particular location and also that they occur simultaneously. However, to a layman like me, the advent of Special Relativity seems to have changed the concurrence between the two in the following way: We can no longer take it for granted that coexisting events that are not coterminous will also be simultaneous, because in Einstein’s original thought experiment (train/embankment) where he outlines his “most natural de…

Well GR 's equations show(I have to take this on trust as I have not learned them personally) that sources of mass and energy curve neighbouring spacetime with the result that bodies move along the geodesics and that we see as them "falling" towards that source ,when account is taken of their existing momentum. Why do these bodies move "down" rather than "up"? Is there something in the equations that only allows them to ,as it were be attracted rather than repelled by the sources of mass-energy?

Hi everyone, According to special relativity, time slows down or speeds up according to how fast you are moving relative to something else. As I understand it, the light traveling from something that tells time reaches you slowly when you are traveling near the speed of light and that is why time slows down. I do not understand why the light from time reaching you more slowly means that time has slowed down? The time it takes for a second to pass is called a second, any slower time or faster time is not a second. A second passing slowly means that a second will pass slower than the time we call a second, which would mean that time is not a second because it is …

I have just come across this terminology and wonder how it works (also eager to "blood" my use of the term ) So,if we have a massive body far removed from other such bodies,I understand that it will curve the surrounding spacetime(or create a gravitational field) So my question is "Does this gravitational mass dissipate as a result of having caused this effect"? And ,perhaps relatedly does the Gravitational field created by this massive body expand at the speed of c from the massive body in a similar way to how an em wave does (as an expanding sphere)? If it does ,does it carry away the mass of the body so that it dissipates eventually?

I'll try this again! What's important in the twin paradox, which results in the asymmetry between the twins, is that one of the twins remains in an inertial frame while the other uses primarily two different inertial frames. It is tempting then to think that a mechanical switch between the frames somehow "causes" the relativistic effects---and further that the only way to switch frames is to accelerate---but this is not true. This can be shown by running the experiment with 3 moving clocks, none of which needs to accelerate during the experiment. Start with 2 passing clocks, A and B, which are each set to zero at passing. Let B travel some distance at v…

The twin paradox doesn't require an inertial twin. Suppose two twins left Earth at the same time and returned at the same time, each traveling a different but constant speed relative to Earth. Whom does your intuition say traveled a longer distance, the twin who ages more, or less? Don't read the following puzzle if you want to think about it first. Spoiler Two twins leave Earth at the same time and return at the same time, each traveling at a respective constant speed relative to Earth. Each measures the distance she traveled, and the time it takes. They find that one aged twice as much as the other, and they traveled the same distance. What were …

I was woundering why time slows down when you go faster then the speed of light

how relativity which explicitly says that nothing with mass can travel faster than the speed of light predicts something with the mass of an entire galaxy moving faster than the speed of light is predicted by relativity which forbids this?

I find it hard to understand General Relativity when it is casually referred to as curvature in spacetime or as the sagging in a trampoline mat. Would a better explanation for the novice be to say things fall because they are seeking out the place where time runs the slowest? For instance, when explaining how light is deflected as it passes close to a star imagine it surrounded by voxels (3D blocks of space). Time runs slowest in the voxels close to the star. Because the speed of light is constant in all frames of reference and as speed = distance /time the voxels close to the star would appear to be smaller to the photons of light. Consequently the quickest…

A key premise of relativity is that there is not a fundamental frame of reference that is above all other frames of reference. But this seems to lead to a logical conflict when explaining how clocks lose time when they travel in a round trip (the travelling twin scenario). Please can the steps of how the travelling clock loses time with respect to the stay at home clock be walked through, with particular focus on why the following is not a problem... A recent post discussed travelling clocks and rulers. The conclusion with regards to rulers, was that a travelling ruler does not physically change its length compared to a stay at home ruler. Although each frame…

Is this explanation ok that avoids using forces? Thanks Rather than twin flying it is best to consider synchronised clocks. This avoids talking about acceleration at certain times is the flight. Special relativity doesn’t require an understanding of acceleration – this is dealt with in general relativity. It is not necessary for an actual twin to follow the out and back path or to experience an acceleration at the turning point. Outgoing and incoming spaceships could simply exchange clock readings or videos when they pass each other. Clock A stays on earth and is synchronised to clock B on a spaceship flying past (3/5c). After 5 earth years the spaceship …

What is time? Some people think of time as a human concept, but to me it seems as if time, to some extent, is woven into the fabric of space. If it weren't, how would space warp time? Someone on the boards(don't remember who) said that time is the direction in which entropy increases. I can't imagine a world without time. If someone/something were to live outside time, what would it be like? Would there still be cause and effect? When I look at it from that perspective, it seems as is time exists only in our heads. :shrug:

in long distances (megaparsec level) does the accelerating expansion of the universe affect on light and it's trajectory?

I have a basic question that I've never actually seen answered in discussions of LIGO and gravitational waves: if these waves are warping space itself (actually spacetime), then all matter occuping that space will be warped to exactly the same degree that space is warped, making such warps in principle undetectable. So if an interferometer like LIGO, with two perpendicular arms, is set up to measure such waves, what is it actually measuring? Any distortion of the arms in the direction of the waves will not be detected because that arm(s) will be distorted to exactly the same degree that space itself is distorted. Help?

Ah yes. This is much easier to say than to prove. What about quarks. Quarks can anihilate into photons. You would say that quarks are made of photons. But what about QCD interactions which give quarks to gluons? Are quarks made of gluons? (No.) How can quarks be made of photons AND gluons? Well, could gluons be made of photons? Absolutely not. Gluons carry color charge, and photons are color neutral. If photons were NOT color neutral, QCD would be spontaneously broken and there would be no neuclei, and (sadly, for some I guess) no Farsight. What about electroweak processes where electrons go to W and Z bosons? How can electrons be made of both W and Z …

ok people, let me tell you this; Tesla and Einstein, in my opinion, have been the two most successful physicist of the 20th century. The problem is that Tesla didn't get what he deserved, while Einstein's name lived out to be the most popular name of the 20th Century (and if I've been informed accurately Tesla is not mentioned much in US school textbooks nor Australian or UK textbooks and most of the students wouldn't have idea of who the hell Nikola Tesla is - and probably many who are reading this thread would've asked themselves the same question). Well, I'm using Einstein just for a comparison in this thread, the main character here is Nikola Tesla. Let's just…

I've been thinking about how to do it and came up with these theories. Travelling to the future or past using the closer to the speed of light you travel the slower time passes for you law of relativity. I think you can travel into Earths future by getting in a space ship and travelling really fast for a few years. So what?? It'll be easier for us to perfect cryogenic suspension or whatever and travel into Earths future without even aging a day never mind a few years. So it's pretty pointless using high speed to travel into Earths future faster than you already are. Travelling faster than the speed of light, why do people think once you pass the speed of light…

When a rocket is standing on earth the time in the top is going faster that the time at ground/rocket-engine level due to gravitational time-dilation. Using the equivalence principle with the same rocket accelerating in deep space, again an observer in the top will see the time passing by faster in the top then a traveler at rocket-engine level. To me this looks like a contradiction because they both will experience the same acceleration and duration of acceleration! I am confused: how is this possible? What am i missing?