Gravity (from Latin gravitas 'weight'), or gravitation, is a natural phenomenon by which all things with mass or energy—including planets, stars, galaxies, and even light—are attracted to (or gravitate toward) one another. On Earth, gravity gives weight to physical objects, and the Moon's gravity causes the ocean tides. The gravitational attraction of the original gaseous matter present in the Universe caused it to begin coalescing and forming stars and caused the stars to group together into galaxies, so gravity is responsible for many of the large-scale structures in the Universe. Gravity has an infinite range, although its effects become weaker as objects get further away.
Gravity is most accurately described by the general theory of relativity (proposed by Albert Einstein in 1915), which describes gravity not as a force, but as a consequence of masses moving along geodesic lines in a curved spacetime caused by the uneven distribution of mass. The most extreme example of this curvature of spacetime is a black hole, from which nothing—not even light—can escape once past the black hole's event horizon. However, for most applications, gravity is well approximated by Newton's law of universal gravitation, which describes gravity as a force causing any two bodies to be attracted toward each other, with magnitude proportional to the product of their masses and inversely proportional to the square of the distance between them.
Gravity is the weakest of the four fundamental interactions of physics, approximately 1038 times weaker than the strong interaction, 1036 times weaker than the electromagnetic force and 1029 times weaker than the weak interaction. As a consequence, it has no significant influence at the level of subatomic particles. In contrast, it is the dominant interaction at the macroscopic scale, and is the cause of the formation, shape and trajectory (orbit) of astronomical bodies.
Current models of particle physics imply that the earliest instance of gravity in the Universe, possibly in the form of quantum gravity, supergravity or a gravitational singularity, along with ordinary space and time, developed during the Planck epoch (up to 10−43 seconds after the birth of the Universe), possibly from a primeval state, such as a false vacuum, quantum vacuum or virtual particle, in a currently unknown manner. Attempts to develop a theory of gravity consistent with quantum mechanics, a quantum gravity theory, which would allow gravity to be united in a common mathematical framework (a theory of everything) with the other three fundamental interactions of physics, are a current area of research.
Homework Statement
-Two objects of negligable radius and masses M and m are fixed in space at the distance R. Gravity is the only force acting between those two bodies. At some point in time, body of mass m is realized and starts moving due to gravity toward statical mass M.
Find v(x) and...
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...
Homework Statement
I have two objects that slide without friction on a circle of radius R, oriented in a
vertical plane, as seen on the attached photo.
The heavier object (mass = 3m) is attached to a spring with an unstretched length of zero and spring constant k. The fixed end of the spring...
That is to say, how does time behave in a region of space where multiple gravitational fields cancel out their accelerating effects?
I understand that time "slows down" in a gravitational field, but does this depend on the actual presence of the field, or instead the actual net acceleration...
Feel free to correct anything I state here. I'm trying my best to understand some rather complex (for me) ideas about time dilation.
So if I understand correctly, increasing velocity compresses time, causing you to exist more slowly relative to anyone not moving at that velocity. Similarly, the...
In his recent letter to the physics community, Susskind says Gravity and Quantum Mechanics is inseparable. Read it here .
Frankly, I do not fully understand his letter or the claim that he is making.
What do you think?
the news are reporting this paper
Ghirardi-Rimini-Weber model with massive flashes
Antoine Tilloy
(Submitted on 12 Sep 2017)
We introduce a modification of the Ghirardi-Rimini-Weber (GRW) model in which the flashes (or collapse space-time events) source a classical gravitational field. The...
I want to demonstrate to flat earthers that water does indeed stick to a ball. If we want to do a scale model of the earth, at which radius will gravity overcome the surface tension?
Is gravity an attractive force of matter, or is it a universal force of expansion and pressure that exists in apparently empty space? Does matter attract objects near it, or does matter merely block gravity pressure on on any given side of a material body, giving the illusion that the matter...
Now, I know that it is theoretically possible for negative mass to exist and for negative energy to exist. But any gravity would act on all objects and all energy, no matter if that mass and energy is positive or negative. So negative gravity would for example, pull a person upwards. Now yes, I...
Hey guys,
I'm itching to find out what you know or theories about gravity and light...
My first question that I pose to you is this..
If the cosmic speed limit is set by light.. then why can gravity affect it?
Consider this.
Light is traveling away from a black hole.. gravity is so...
I have read on the internet that if an object rests on a table, that object will exert the force of its weight on the table. But, for some reason, that doesn't make sense to me. If I have a 10 kg book that rests on a table, the gravitational force on that object will be 98 N. If gravity is...
If I drive a plane and the force of engine is bigger than force of gravity of it , if the engine is turn on always ,and assuming no air , will the plane continue moving up and escape from the gravity ?
I would have thought that this would have been tested before but this paper suggests that it is a new theory.
arXiv:1709.02481 [pdf, other]
A possible explanation for dark matter and dark energy consistent with the Standard Model of particle physics and General Relativity
A. Deur
Comments: 6...
I'd like to ask about a hypothetical situation. A human, wearing a jetpack, for example, accelerates forward with 200,000 m/s^2 and therefore, experiencing extreme g-force of roughly 20,408 g. If there will be a hypothetical device that will be able to redirect the gravity force (g) to elswhere...
Physicists had success in developing a relativistic quantum mechanics, also Quantum Field theory.
I wonder why it's not the same with a quantum gravity theory. I suppose this is mainly because we do not have good emphirical information from a place where Einstein's theory fails: black holes...
Preface
There are lots of times in physics when we use approximations of a more accurate or fundamental physics theory because it is easier to work with.
For example, in quantum chromodynamics (QCD) lots of calculations are done using the Schwinger-Dyson equations rather than the actual...
Homework Statement
1. Homework Statement The Earth turns once around its axis in 24.0 hours. We will assume that it is perfectly spherical, with radius 6400 km. The mass of the Earth is taken to be 6.00 × 1024 kg. The gravitational acceleration on the surface is taken to be g = 9.80 m/s2 .
a)...
Using special relativistic calculation it can be showed that magnetism is a result of electric charges in motion. using the same argument, why can't we find a magnetic force like thing for gravity?
Please see the below image, it is a closed and well sealed circulated pipe structure, fully filled with water and no air inside. The density of that green object is greater than water (say 1.2 while water is 1). In this situation, will the green object be sunk? Better with some explanations...
I've seen a little bit about the gravity light. I think it works in a simple way, a weight at a certain height has gravitational potential energy depending on how far the weight will fall, this quantity represents the total energy we have at our disposal to power a light. Now we normally think...
Can someone please tell me how the energy field created by warped space (gravity) and centred at the Earth's core dissipates? Is it the pressure/compression of this force/energy that makes the core so volatile?
Whilst time slows at altitude, do we become lighter, as we are further away from...
I know two essential points where General Relativity plays a central role in String Theory:
i) definition of the theory using a target spacetime with some Riemannian background metric in the Polyakov action and
ii) recovery of the Einstein field equations as conditions regarding conformal...
Hi,
I am seeking to understand better how this well accepted idea:
"...according to general relativity, gravity is a manifestation of the geometry of spacetime."
(https://en.wikipedia.org/wiki/Loop_quantum_gravity)
is compatible with the equally well accepted idea that gravity travels at the...
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...
I'd be extremely grateful if anyone could help me with this ... its mainly part iv) that I'm stuck on but the other parts build up to it! Thanks very much!
1. Homework Statement
I have a wheel shaped space station of radius 100m rotating about its symmetry axis (defined to be the z axis) at...
If I understand space time correctly Gravity is not a force acting on a body but rather the effect of a mass on space time causing a distortion which effects the movement of another mass through that space time.
If Gravity is not an actual force then there are only three forces left to be...
Okay, I know there are many other discussions regarding this exact topic, but I might (probably not) have found an easier way to think of gravity being a force or not a force.
Just like light can be a particle or a wave from how you measure it, to my understanding so can gravity. As I am told...
If an object was to lose its gravity for any reason, would it lose its reference frame to the planet and sun. Therefore keep going in a straight line? Or is there some other force that would keep it pinned to the planet. Also does this have any application to sci-fi anti gravity would it also...
As I understand, under Newtonian Gravity, there are no limits for the length of the gravitational influence of an object, except the speed of causality and the age of that object. So, considering the Sun as an example, which is roughly 4.6 billion years old, its gravitational influence would...
Hello!
Can you tell me how to calculate the gravitational force between two extended inhomogeneous bodies? (In the general case, we don't know anything about the shapes, we only know the density of masses)
The measurement of g appears to be somewhat limited in extent. You either have simple pendulum experiments that yield something like 10 +- 0.5 or so m/s^2 or - at the other extreme - very expensive gravimeters which will measure to a few ppb. Not much in between.
However an educationally useful...
I understand the goldilocks zone but would like to know if there are similar limits with respect to supporting life as we know it for a planets gravitational force (min/max) and atmosphere pressure (min/max.) I understand gravity can affect pressure but so can the amount of atmosphere and do not...
I would like to know the difference between this two concepts, specially the difference between the geometry deformations of space-time that they descript. As far as I know the Schawrzschild metric can be represent by Flamm’s paraboloid, but this shape is not the same that the deformation of...
Homework Statement
Two small spheres of 15 g each are suspended from a common point by threads of length 35 cm. Each thread makes an angle with the vertical of 20 degrees. Each sphere carries the same charge. Find the magnitude of this charge.
(The correct answer is: 0.58 μC)Homework Equations...
Homework Statement
A satellite is orbiting the Earth around an orbit of radius R=2.5R0, where R0 is Earth's radius. What additional velocity is needs to be directed along the radius of the orbit so that satellite escapes Earth's gravity?
Homework Equations
Total Energy= K + U
Conservation of...
Can anyone give a good overview of Horava gravity for a layman. I have only read one thing on it in the Scientific American going back to 2009. Where does it stand today ? How is it understood? Wha are its strengths and weaknesses?
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...
One way to get the universe to expand is with dark energy that pulls at the matter of the galaxy separating it or equivalently for space-time to not be perfectly flat.
An alternative, in principle, would be for the gravitational pull between objects like galaxies and galactic clusters to be...
I want to determine the acceleration due to gravity at a place using a helical spring.
For this, I've first calculated the extension in length of the spring (##x##) for a particular load (##L##) on the pan. Then I've plotted a graph for ##L## vs ##x## for different values of L and corresponding...
Pardon me if this seems like an incredibly naive question. Perhaps the question could also be rephrased as such: "Why do the laws of classical mechanics hold true with Earth as a frame of reference?"
A quick google search turned up the usual answer: the Earth rotates at a constant speed...
From the eqn of motion deduced, I can say that two body, one of 50 kg, and one of 50 g if allowed to freely fall from same height, they will reach the ground the exact same time?? Practically is it possible? How ? They are largely different but same distance in same time?
I recently read an interesting article published in Physical Review Letters in October 2014 - "Identification of a Gravitational Arrow of Time." There were also other articles in several general interest science magazines...
Hi there. I was wondering that if mini or micro black holes could theoretically exist, and if not all black holes need to "devour' matter, then could it be possible that all things we perceive to have gravity could possibly be caused by a mini or micro black hole at the center of massive objects...
Hi all,my second question is this.Why don't galaxies obey gravity? In our solar system the closer to our sun the planet is the faster it rotates.So the outer planet takes much longer for a solar year.
When we look at galaxies this gravitational law doesn't apply.The outside stars spin at the...
Suppose I fell from a mountain, which would hurt less:
A) Falling on a very huge pile of powder snow or
B) Falling on water
It's a serious questions! Thanks!
Thanks for visiting and reading this imaginary thread.
So, recently I tried to write a novel. It is an ongoing project, and very far from completition. I've read so many Sci-Fi stories before, and some do not follow general physics very well. I want to make a world that is believable, but also...