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.
I derived the formula for the quadrupole radiation power emitted by a system of masses:
$$P=\frac{1}{45}\dddot{Q}_{kl}\dddot{Q}_{kl} .\quad\quad (*)$$ Note here that: (1) I am using geometrized units, so ##c=G=1##; (2) ##Q_{kl}## is the quadrupole tensor $$Q_{kl} = \int{(3x_k x_l - δ_{kl}\cdot...
Gravity is considered as a bending of spacetime due to massive objects. And hence other objects around the curvature follow a geodesic path. My question is, why do they follow the path? Can't they be stationary? What's the cause behind objects even moving in the first place? I sometimes hear the...
I just saw a StarTalk video where Neil deGrasse Tyson says that gravity at the poles is lower than at the equator because, even though you are closer to the center, the mass around the equator outside the sphere below you somehow does not count (skip to 4:21 in the video). He is obviously wrong...
How do proponents of modified gravity explain the fact of observation of galaxies, the behaviour of matter in which does not require an explanation in the form of dark matter or modified gravity?
So one of the major topics in physics is trying to reconcile quantum mechanics and general relativity.
And the classical expression of electromagnetism is Maxwell's equations, and its linked to quantum models of electromagnetism.
And then there's also a gravitational analogue of Maxwell's...
[Mentor Note: Thread moved from the schoolwork forums to the technical forums, since it appears to be a real-world problem]
If I have a water well 55m deep
I want to suck water by gravity without any pump.
I put a barrel of 85 liters and connect it firmly to a pipe of 55m length going into...
As bodies orbit each other they emit gravitational waves (presumably by emitting gravitons). There could be configurations of several moons around a planet (for instance) where the quadrupole moment does not change and is invariant. However, there could still be higher order effects, namely...
If I'm not mistaken, in interstellar gas, there can be clouds of free electrons (not "attached" to any atomic nucleus)
But can they stay like that indefinetely? Or will they inevitably end up in atoms?
And how are they holding in interstellar gas inside of galaxies? Are they gravitationally...
Consider a halo made up from massive and stable particles like neutrinos* (let's not consider protons which, although we don't have any experimental evidence showing that they are unstable and decaying, there are some GUTs proposing theoretical mechanisms where they could decay over extremely...
in an interview Michio Kaku was asked about Loop Quantum gravity and he replied that it is only a theory of pure gravity, but that the universe also contains particles, the particles of the standard model, and only superstring theory unifies both quantum gravity and the standard model.
the...
I've been reading the book "Classical Mechanics" by John Taylor, and in the chapter about noninertial reference frames, it states that the direction of 𝑔 (the apparent gravity, which includes the centrifugal force) is not necessarily aligned with the direction of 𝑔0 (the true gravity direction...
I will try to hide how unintelligent and uneducated I actually am but I’m sure it’ll be showing throughout this question. My apologies. I really don’t know how else to find answers to questions I have besides coming to you all.
In a nutshell, I’m trying to understand why an astronaut floats...
I am an author/novelist and I'm working on a huge science/fantasy project that's been in development for the past 5 years, and as a science fiction fan I've always hated when people get the science really wrong.
So my question is: how would the gravity of another planet influence human...
okay I annotated the diagram given and the grey thing where they take y axis up as positive is what I understand to be, right?
But in the answers, they start off by going V = u - gt. They've taken acceleration due to gravity as a negative value. Why? I thought the skateboarder was falling...
I can calculate the COG with the above formula however P2 is unknown.
I need to be able to put P2 into another function which will check that the vector A->COG is parallel to the nominated angle. I cannot seem to work this one out algebraically.
Any assistance or guidance would be appreciated.
Imagine making a hole in the ground, about a mile deep, with a large and square diameter. In the middle of the hole, there is a hollow and narrow tube with all air sucked out. Next to one of the walls, so close that it's touching, there is another hollow tube without air inside. Two identical...
This question was not my idea. I heard it while watching a YouTube video hosted by a celebrity astrophysicist and a comedian. This astrophysicist answers the physics questions of his Patreon supporters, and one of the supporters asked him about the spaghettification of quarks. I'm paraphrasing...
Imagine we have a cold region of the universe, almost devoid of matter and radiation. Or perhaps in a future universe where the CMB has "cooled" down to sufficiently low "temperatures"
Could there be long lived macroscopic Bose-Einstein and Fermionic states of matter there? Could matter...
I have a question that I have been unable to find an answer to.
The question is does matter "create" space?
Some places I read that space "just is", and matter fills it and creates its gravitational curving. But that something "just is" is supremely unsatisfying as far as answers go.
Another...
This may already have been answered but I can’t find it.
If organic matter is disturbed, exp. on the moon, does the matter experience a gravitational pull?
In reading Weinberg volume 1 I learned gravity is not renormalizable by Dyson power counting. This means that it has an infinite number of free parameters, and such theories lose their predictive power at energies of the common mass scale. This being said, T Hooft and Veltman showed miraculously...
What is the consequence of the center of gravity passing below the rod in the high jump? Fosbury flop.
Which equation is responsible for a bike being more stable the faster it's driven? and in rotating things in general being more stable the faster they're rotating.
Looking out the window on recent flights I have given some thought to the implications of the fact the bodies of water we see are never actually flat, anywhere, at any size.
The earth beneath the bodies of water on its surface takes on the shape of a sphere of course, and one could say that...
If gravity is caused by the warping of spacetime - how did gravity compress the mass of the post Big Bang universe? Does said compression indicate the force of gravity exists independent of space time? Was Newtonian gravity responsible for the compression? On the other hand, if spacetime was the...
A double-slit experiment can be run and get similar results using either photons or small particles that have mass, such as molecules. Why doesn't the gravitational field of molecules in the experiment reveal which-way information to the surrounding environment, and trigger decoherence and loss...
Hello community,
I am currently designing a gravity-based electricity generator and exploring the feasibility of different setups using a 500 kg mass. The core of my project is to harness the potential energy from this mass as it is lowered from a significant height. I am considering several...
You have a rope hanging over a fixed support with a heavy weight at one end and a lighter weight at the other end. You set the end of the rope with the lighter weight spinning in a circle and let the heavy weight end fall under gravity. As the heavy end falls the length of the rope that is...
The existence of dark matter was initially proposed to address discrepancies between observed galaxy rotation curves and the expected behavior dictated by our current understanding of gravity. Typically, it's argued that stars at the edges of galaxies rotate faster than expected, leading to...
Black holes accrete mass around them and it falls gradually up to the even horizon where mass is trapped by the black hole forever. However, the rate of mass falling from the accretion disk to the black hole ranges from being very fast to very long-lived, depending on various conditions...
2 recent gains on loop quantum gravity theory
arXiv:2403.18606 (gr-qc)
[Submitted on 27 Mar 2024]
Test the Loop Quantum Gravity Theory via the Lensing Effect
Lai Zhao, Meirong Tang, Zhaoyi Xu
https://doi.org/10.48550/arXiv.2403.18606
and
[Submitted on 7 Dec 2023 (v1), last revised 28 Dec...
from ...
www.physicsclassroom.com/class/1DKin/Lesson-5/The-Big-Misconception
"Free-fall is the motion of objects that move under the sole influence of gravity; free-falling objects do not encounter air resistance.
Huh ?? of course it encounters air resistance, doesnt it ?
An object...
shouldn't it be a sort of partially GR and partially QM?
I mean in a sort of superposition of both theories such that in the specific limit becomes GR and another limit QM, and in the between both regions it's something entirely else, not QM and not GR.
Is this possible?
I haven't yet done the...
This question is mainly for @A. Neumaier, but I post it in public in case others are interested.
The usual reason given for needing to quantize gravity is, heuristically, that, in the presence of quantized stress-energy where there can be a superposition of different stress-energy tensors...
In discussions about simulating gravity in a spaceship by the use of tethered masses revolving around a common centre, the assumption appears to be that these masses must be equal. Would instabilities occur were this not the case? Or would the problem go away simply by placing the hub at an...
Can the force of gravity overcome the Planck force?
I remember that a long time ago I read that in the universe the Planck force was the maximum force that could be reached. But when Sagittarius A and the black hole at the center of the Andomeda galaxy approach, I have made the calculation that...
I don't know complex mathematics about general theory of relativity but i tried to understand it from internet. Somewhere i heard that in GTR gravity is explained as curvature of space-time not as force as in Newton's laws. If GTR doesn't explains gravity as force then why G which is constant of...
I've never had any physics class before so please bare with me on my lack of understanding.
I've been thinking about gravity and its relation to entropy lately and was wondering if my thinking is correct.
Entropy seems to be an opposing force to gravity. where gravity is creating gradients...
The Wikipedia article on Quantum Gravity reads: "The observation that all fundamental forces except gravity have one or more known messenger particles leads researchers to believe that at least one must exist for gravity. This hypothetical particle is known as the graviton"
To which... yikes...
Stars have mass. This mass has a gravitational pull. The nuclear fission of the star pushes against the effects of gravity. Why doesn't the gravity reduce as the star burns more and more of the hydrogen/helium/carbon that it's made up of? In other words, how can a black hole be created when the...
I want to emphasize that I am not familiar with general relativity.
Consider a system of particles with masses ##m_i## in gravitational field of another body ##A##. Total gravitational force exerted on ##A## will not be $$\sum G \frac{m_i m_A}{r^2}$$ where ##r## is distance between system and...
Hi Pfs,
I read somewhere that if the graviton had a spin 1, then gravity would be repelling.
Is there a formula showing that the attract-repel depends on the parity of the carrier's spin?
thanks
Hey there,
I just want to know if objects with small mass have their own gravity. To think of it they must have gravity as all matter with mass have gravity. When such a small mass is dropped one meter above the surface of earth would the earths and the small mass gravity combine? If so...
I started by calculating the energy at the Earths surface, which is just -G(150)(6 x 10^24)/(6400 x 10^3) = -0.9 x 10^10, and calculating the energy at the orbit radius, E = -G(150)(6 x 10^24)/(18000 x 10^3) = -3.4 x 10^9, then doing some subtraction we have -3.4 x 10^9 - (-0.9 x 10^10) = 5600 x...
I had a question about this paper (https://arxiv.org/abs/1401.3742)
There, the authors indicate that dark energy competes against gravity in oversdensities and can slow down or even prevent their collapse.
I have a simple question about this:
Galaxies will in principle evaporate their outer...
Is it possible that MOND might be standard gravity plus an additional force that is inversely proportional to distance. One that is also a property of matter?
I ask, because viewing this way begs the questions: If two, then why not more, and if more then perhaps a series with a hope of...
To do this apparently, you need to use the work-energy theorem. You can calculate work done by gravity easily. However it was said that work done by the reaction forces from the hinge is zero, I don't get why.
Reaction Force from the hinge is an external force on the rod, and all external...