What is Relativity: Definition and 997 Discussions

The theory of relativity usually encompasses two interrelated theories by Albert Einstein: special relativity and general relativity, proposed and published in 1905 and 1915, respectively. Special relativity applies to all physical phenomena in the absence of gravity. General relativity explains the law of gravitation and its relation to other forces of nature. It applies to the cosmological and astrophysical realm, including astronomy.The theory transformed theoretical physics and astronomy during the 20th century, superseding a 200-year-old theory of mechanics created primarily by Isaac Newton. It introduced concepts including spacetime as a unified entity of space and time, relativity of simultaneity, kinematic and gravitational time dilation, and length contraction. In the field of physics, relativity improved the science of elementary particles and their fundamental interactions, along with ushering in the nuclear age. With relativity, cosmology and astrophysics predicted extraordinary astronomical phenomena such as neutron stars, black holes, and gravitational waves.

View More On Wikipedia.org
Recent contents Top users
  1. Santilopez10

    I Help with special relativity mathematics

    I am having a hard time trying to understand this transformation from lorentz:https://imgur.com/a/WYWMO (You should ignore the spanish part and just focus on the math). I can’t understand well why they turn into what you can see in the second picture, when taking really small values of x...
  2. T

    How Does Invariance Apply in Relativity Theory?

    Homework Statement Homework EquationsThe Attempt at a Solution ok so for w' i am getting since the s' is only moving in x direction ## \omega' = \omega \gamma (1 + \beta) ## is this correct then i am having some trouble in dealing with the dot product to derive for ## \bf {ck'} ##
  3. jgarrel

    General relativity- Coordinate/metric transformations

    Homework Statement Consider the metric ds2=(u2-v2)(du2 -dv2). I have to find a coordinate system (t,x), such that ds2=dt2-dx2. The same for the metric: ds2=dv2-v2du2. Homework Equations General coordinate transformation, ds2=gabdxadxb The Attempt at a Solution I started with a general...
  4. F

    I Questions about the general principle of relativity

    One of the founding principles in GR is the principle of general relativity, which loosely states that all coordinate frames (inertial and non-inertial) are equivalent in the sense that the laws of physics are invariant. My question is, does the justification for this come from Einstein's...
  5. G

    I Does Gravity Change Space Density? Exploring Everything and Nothing

    I was watching a movie called Everything and Nothing. It got me thinking. For the sake of argument pretend that you could make the sun pop in and out of existence. If you were to measure the distance between two points on the other side of the solar system with no sun, then if the sun were to...
  6. J

    I Is MWI the Only Solution for Saving the Principle of Relativity?

    Hi guys, I am new to physics forums and am an undergrad who is really interested in the philosophical implications of quantum physics. I know this isn’t a philosophy forum but upon skimming older threads regarding MWI I have come across an interesting number of posts by a few members named...
  7. B

    I Dirac Matrices and the Pythagorean Theorem

    I understand that momentum, rest mass and energy can be put on the sides of a right triangle such that the Pythagorean Theorem suggests E^2=p^2+m^2. I understand that the Dirac equation says E=aypy+axpx+azpz+Bm and that when we square both sides the momentum and mass terms square while the cross...
  8. C

    I Electrical Current Repelling Magnets Due to Relativity

    I recently watched this Varitasium video where he explains the magnetic field due to a current carrying wire. In the video he explains how what we see and describe as the magnetic field produced by a current carrying wire is actually just a electric force caused by the an imbalance of charges...
  9. A

    B Resolving the Relativity of Simultaneity: A Geometric Approach

    Hi, I read through einsteins popular book on relativity translated into english around 1922 and subsequently read the original 1905 paper on the electrodynamics of moving bodies. So we have a fixed observer seeing flashes happening at the same time and we have a moving observer seeing one...
  10. T

    I Singularities in General Relativity

    There are two kind of singularities which are familiar in General Relativity. One of them is the singularity of Black Holes and the other is at the beggining of the universe. I'm confortable with the former singularity --it seems to make sense. But as with the latter, I'm not so confortable...
  11. Megaton

    B Can General Relativity and Quantum Field Theory Be Reconciled?

    Please don't kill me here...I am really just a curious creature...QFT and GR are mutually incapabatable ergo they cannot both be correct...so best is that one is used for low energy large scale predictions (as per theory) and small scale high energies ( as part theory) ...(BTW I know what the...
  12. A

    A Relativity implies antimatter?

    https://arxiv.org/pdf/hep-ph/0609174.pdf page 8. 2.1.2 Special Relativity Requires Antiparticles This article describes a scenario in which atom A releases an electron which is absorbed by atom B. A=> A+ and B => B- However in a different inertial frame (F) it is possible due to Heisenberg's...
  13. P

    B Time Dilation: Moving Rocket 0.5c vs Accelerating Rocket 0.5c

    A non-moving observer is looking at two different rockets in space. One rocket is moving at a steady velocity of 0.5c, and the other rocket is currently moving in 0.5c but has steadily accelerated from 0.3c and will continue accelerating until it gets to 0.7c. Assuming that there is no...
  14. S

    B Volumes and Hyper Volumes Related Special Relativity

    How can volumes and hypervolumes be related to Einstein's theory of special relativity and to quantum mechanics? Also, can volumes and hypervolumes of objects be used for modeling how different scenarios can change over time? Oh yeah, and hi my name is Sasha Jaffarove!
  15. A

    B According to General Relativity, would the Earth be 'flat'?

    I thought about the geometry of Earth by definition and thought of the implications of 'curved space-time'. I understand a trajectory of a satellite and other objects to be straight geodesics through warped space-time. Would the Earth then therefore be able to described as a straight surface in...
  16. P

    The electric field in an expanding, statically-charged tube

    Imagine that I have a straight, statically-charged, cylinder-shaped tube with arbitrary (ideally infinite) extent. The charge is distributed evenly over the tube such that the field inside the tube is zero. For convenience, let's line up the tube centered along the x-axis such that the...
  17. T

    Acceleration in special relativity

    Homework Statement Homework EquationsThe Attempt at a Solution it is known that ##a_0 ##is the proper acceleration ## a= \frac{a_0}{\gamma^3} ## hence integrating it gets ## v = \frac{a_0t}{\sqrt{1 + (\frac{a_0 t}{c})^2}} ## but this is in terms of t how to make it in terms of t'
  18. J

    B Postulates of General Relativity

    Hi guys, A real easy one. Are the following postulates completely true about general relativity as they are pretty amazing to me. 1) Black holes are a solution to his field equations for GR (or are predicted by the theory) 2) His field equations also suggested the universe was expanding 3)...
  19. P

    Dust in special relativity - conservation of particle number

    Homework Statement My textbook states: Since the number of particles of dust is conserved we also have the conservation equation $$\nabla_\mu (\rho u^\mu)=0$$ Where ##\rho=nm=N/(\mathrm{d}x \cdot \mathrm{d}y \cdot \mathrm{d}z) m## is the mass per infinitesimal volume and ## (u^\mu) ## is...
  20. P

    Emitting one or two opposite charges along the x-axis

    Let's consider that I have an emitter that can emit both negative and positive electric charges. Here let's consider only scenarios with two particles (one negative and one positive) that start initially at the tip of some electrode, where one or both the charges will separate from at the same...
  21. M

    Relativity: Initial velocity and e/m of Thomson's experiment

    Homework Statement In an experiment similar to Thomson’s, we use deflecting plates 5 cm in length with an electric field of 1.0×10^4 V/m. Without the magnetic field, we find an angular deflection of 30°, and with a magnetic field of 8×10^-4 T we find no deflection. What is the initial velocity...
  22. Moayd Shagaf

    Relativity Learning Einstein's General Relativity

    So, I'm going to learn general relativity but I'm confused in which book I start with Bernard Schutz book seems excellent but I'm more interested in d'Inverno book, And Misner/Throne Book Seems complete but its giant and good for reference, So I think I will go with d'Inverno , but first I need...
  23. L

    Relativistic Doppler Shift for Transverse Movement

    Homework Statement A sodium light source moves in a horizontal circle at a constant speed of 0.100c while emitting light at the proper wavelength of λ0=589 nm. Wavelength l is measured for that light by a detector fixed at the center of the circle. What is the wavelength shift λ-λ0? Homework...
  24. M

    B Could this FTL idea with a fast moving large mass be possibl

    Could this FTL idea with a fast moving large mass be possible? I have recently come up with a possible way to achieve faster-than-light (FTL) travel by using a high speed singularity or large mass. Background As everyone knows, according to relativity, under normal conditions, it is impossible...
  25. D

    Simple Special Relativity Problem of Length Contraction

    Hello, I'm self-studying Ta-Pei Cheng's Relativity, Gravitation and Cosmology. Problem 2.8 is the following: Two spaceships traveling in opposite directions pass one another at a relative speed of ##1.25 \times 10^8## m/s. The clock on one spaceship records a time duration of ##9.1 \times...
  26. jedishrfu

    B Solving Mysterious Relativity Paradox: New Derivation of E=mc^2

    Interesting new derivation of ##E=mc^2## from an experiment of moving atoms emitting photons. http://flip.it/AfcjP9 http://flip.it/AfcjP9
  27. T

    A Unstable 5D Theories: The Search for Stable Black Holes in Higher Dimensions

    I tried a cursory search for this but couldn't find it. I was talking with my advisor about 5D theories such as those of Paul Wesson and Randall-Sundrum, and he said that I shouldn't spend too much time studying those theories because they are unstable, or require so many corrections to...
  28. T

    Basic Question about Relativity Reference Frame Shifts

    Homework Statement I'm using Shankar's Introductory Physics course and I can't get a question out of my head regarding his setup of Relativity. There are two observers, S and S'. Observer S is stationary, while Observer S' is sliding past S (to the right) with velocity u. They agree to set...
  29. K

    I Force on an Object according to the General theory of relativity

    What is the force acting on an object according to general theory of relativity? If there is a such a force, can we predict the motion of an object in general relativity just using the modified Newtons laws of mechanics i.e using relativistic mass of an object instead of rest mass ?
  30. senatorarmstrong

    Calculating the Travel Time of High-Energy Particles Across Our Galaxy

    Homework Statement Our galaxy is about 10^5 light-years across, and the most energectic particles known have an energy of about 10^19 eV. How long would it take a proton with this energy to traverse the galaxy as measured from (a) the galaxy and (b) the particle? Homework Equations I...
  31. jlmccart03

    Finding Angle Theta in Relativistic Skydiving Scenario

    Homework Statement A skydiver is strapped to a rocket and shot into outer space. There is no air resistance so he is able to make his arms into a 45° angle with respect to his body and pretend they are "wings." To a stationary observer on the Moon (we will consider the Moon stationary for our...
  32. jlmccart03

    Calculating Relative Velocity and Length Contraction in Special Relativity

    Homework Statement The problem states: Racer A and Racer B have the same care length, but from a spectators view Racer A looks (1/2) that of Racer B. Also Racer B is traveling at a speed v = (c/2). I am to find the spedd of Racer A in the spectators frame of reference. Homework Equations...
  33. C

    Conservation of Linear Momentum and Covariance

    Homework Statement Assume two masses m1' and m2' are moving in the positive x-direction with velocities v1' and v2' as measured by an observer in S' before a collision. After the collision, the two masses stick together and move with velocity v' in S'. Show that if an observer in S' finds...
  34. davidge

    I Solving Quantum Mechanics in Space-Time: Effects of General Relativity

    I have been wondering what effects a quantum mechanical system would cause in space time. Pick a general state of the system. This would not generaly be in one of the energy eigenstates -rather, it would be on a superposition of energy states. Now, each one of them would cause a different space...
  35. T

    I Inflation theory and General Relativity

    Does General Relativity predicts that in the early universe vacuum energy was converted into matter? How does it relates to the Inflation Theory by Allan Guth? I'm asking this because I remember reading in a book on GR that there are ways of calculating the total amount of energy in the...
  36. A

    B Einstein's theory of relativity and time travel

    Hey so from my understanding of Einsteins theory of relativity the closer you travel to the speed of light the slower time is for you, is that right? if it is right does that give to reason that there could be a critical speed past the speed of light for which time for the object traveling at...
  37. jlmccart03

    Galilean Relativity (Invariance) Problem

    Homework Statement Imagine two inertial frames, S and S'. Inertial frame S' moves with velocity v0 = 5 m = s in the upward (positive y) direction as seen by an observer in frame S. Now imagine that a person at rest in frame S throws a ball with mass m straight up into the air with initial...
  38. ISamson

    B Unify General Relativity & Quantum Theory | Stephen Hawking

    Hello, I have read somewhere that the next major step in physics will be unifying general relativity with the quantum theory. Does anyone know about such? I wanted to know a bit more. I have read about such in the book by Stephen Hawking "A Brief History of Time". Thanks, I. P.S. My apologies...
  39. S

    I Applying the Principle of Relativity to Quantum Mechanics

    I read the forum rules, I hope I am not breaking them as these principle is generally accepted and I am not contradicting mainstream science. "The principle of relativity, according to which the laws of physical phenomena should be the same, whether for an observer fixed, or for an observer...
  40. A

    B Special relativity and the flow of time?

    Pardon me if this has been asked before, but I'm confused with the implication that SR makes, that there is no objective moment of present. Do the science still believe that the time flows (i don't mean the arrow of time, but the phenomena of flowing/passing, eq. flowing of a river)? I mean, how...
  41. P

    I Bending of light - caused by gravity or relativity?

    The mainstream interpretation of GRT equations is, that additional double amount of angle of bending of light (Newton vs GRT) is caused by gravity (which is interpreted as curvature of spacetime). But when looking on the equations, it seems that this additional amount of bending is caused by...
  42. I

    Special Relativity: Traveling to Regulus

    Homework Statement A visit to Regulus is on my bucket list. However, it is 77 light years away. Assuming I will live only another 40 years, can I make it to Regulus? How fast would I have to travel (at constant speed) to get there in 40 years? Homework Equations t1 = t0...
  43. C

    I Particle at event horizon as black hole evaporates

    If you are observing a particle enter a black hole, you watch its proper time go to zero at the event horizon as it is 'frozen' there from your frame of reference. What happens in your reference frame as the black hole evaporates? While you can't illuminate where the particle is from your frame...
  44. M

    I Compatibility of Quantum Mechanics and Special Relativity

    Hello, In my free time, I've been learning about an eclectic range of topics (ie. French History, Kinetic Theory etc.). Most recently I've been focused on Quantum Mechanics, which happens to be most complex topic I've ever looked at. Typically I write up summaries after reading from various...
  45. K

    I The spacetime curvature changed by an object

    Does the amount by which an object changes the spacetime curvature depend on relativistic mass or the rest mass? Through this question I just want to answer whether momentum equals [relativistic mass * velocity] or is it [rest mass * gamma * velocity]. Both the formulas might be the same but I...
  46. S

    I Traveling at a speed faster than light

    Imagine yourself to be bat. You can't see anything. You don't have eyes. All you can do is echolocate, using ultrasound. Now imagine something is moving away from you faster than the speed of sound. Can you locate it ? Can you perceive its existence ? If the answer is yes, how ? If no , then...
  47. K

    I Inconsistency in Length contraction

    Let there be 2 astronauts A and B in uniform relative motion and they are moving towards each other. Let A be moving in a spaceship of length L and there are 2 clocks ca1 and ca2 attached to the front and back of the spaceship respectively and let clock of B be cb. The moment when the front of...
  48. D

    B Understanding the probability cloud?

    I understand that the concept of a atom resembling a solar system is disregarded as being untrue because this is based on the Bohr model which doesn't represent how an electron would actually appear in its probability cloud. However, would it be possible that if there were an observer on the...
  49. B

    B What is the reaction to gravity's pull in a vacuum?

    I am trying to understand something. Let me pitch a scenario: You have two asteroids in a vacuum. Each is large enough to be round by gravity. They are separated by roughly the distance from the Earth to the moon. Relative to each other, they are moving at 0 in all directions (aka, they are...
  50. N

    I Relativity of Simultaneity: Analyzing Wavelengths

    Am i right in thinking that relativistic simultaneity explanations tend not to mention the fact that one of the ‘simultaneous’ events may well be red shifted and the other blue shifted and by analysing wavelengths you could presumably work out whether the event was in reality simultanous or not.
Back
Top