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.
We can derive the constancy of the speed of light from Maxwell equations. My questions are: 1. Why it is then need to postulate it when we can obtain it from Maxwell equations?
2. It is stated in many books that gravity wave also propagates with the same speed, c. How do we conclude that? Is...
hello guys, sims back again with another question..
I don't understand what is up with question (b)
cuz like.. to get ##v_esc## we assume that at ##r_0=\inf## ##v=0## but now if I assume at ##r=1.5E8## that ##v=0##.
And then find ##v_esc## from the following:
##\frac12*mv_{esc}^2 -...
Electrons flowing through a resistor are dissipating electrical energy. The electrical energy is transported from the battery to the electrons along the curved field lines of the Poynting vector. It seems like a meaningful idea that electrical energy necessarily travels from the source to the...
I've been thinking about gravity. If mass contracts spacetime, can the warping effects be measured in time as well as spatial distance?
For example -- say you had some matter that suddenly disappeared (please ignore the "how"). Measured in a fixed position, would the gravitational effect drop...
Mentors’ note: this thread is forked from https://www.physicsforums.com/threads/free-fall-in-curved-spacetime.1016510/
But what if the gravity field is homogeneous? Like that of an infinite massive plane? The objects in the ship will stay where they are. An infinite massive plane is quite...
Hello everyone! I noticed in the derivation of potential energy, Mr Lewin defined the gravitational potential energy of a mass m at point P relative to a much larger mass M. He says the potential energy of m at point P is equal to the work he would have to do to move the mass m from infinity to...
We know that gravitational forces are nullified near the center of the Earth, so the gravitational field's influence is not felt. Is it because of the Moon's gravitational field that the area of zero gravity has shifted away from the center of the Earth? If this is the case, this eccentric area...
this paper postulating a minimum gravitational field strength postulating a minimum gravitational field strength (minimum curvature) and a minimum acceleration but otherwise leaving Gr could reproduce MOND
[Submitted on 25 May 2022]
MONG: An extension to galaxy...
I ran into another article demonstrating the Casimir effect and it hit me that zero-point energy is real mass and therefore would have a gravitational influence on our universe. Is there something wrong with this idea, am I missing something?
Hi! Isn't gravity just a smaller object moving toward the lower energy state created by a larger object (time slows down the closer you are to a massive object)? Why do we need a force carrying particle for gravity?
This is my first post so I apologize if i am in error anywhere. I recently had a thought that I have had trouble confirming. Based on the following assumptions.
1.) As you accelerate an object near the speed of light it’s mass increases exponentially.
2.) Mass warps space time.
3.) Spacetime...
since the cosmological constant observed is that there is a small amount of energy in empty space, and in general relativity anytime there is energy there is curvature and therefore gravity, how to calculate gravitational field with dark energy and does it have any observable effects on matter...
A question elsewhere got me thinking about the frequencies/wavelengths of gravitational waves.
The most obvious source of gravitational waves we are finding is from merging black holes, so presumably the orbital period will directly determine the frequency of those waves, yes? So the...
Hello,
This article caught my attention recently and I have several questions on the subject that I'd like to get opinions on.
Before going further, I realize a technical discussion is way past the "I" tags range. Please adjust as necessary and thank you in advance.
My attention was originally...
Hi guys, I have a question that is simple but I do not know how to answer that. It is the following, where does the acceleration of 9,8 meters per second squared go when We're dealing with uniform circular motion? I know that We have the centripetal acceleration that is a vector change, but the...
That may seem like a silly question, but suppose the crew of an interstellar vessel wanted to measure the mass of their ship, perhaps to estimate remaining resources. Unless they have very well calibrated thrust and a very well calibrated accelerometer, the only option is to do so...
The removed mass is ##\frac{1}{8}M##
My idea is to find ##g## from large sphere then minus it with ##g## from small sphere (because of the removed mass):
##g## at A =
$$\frac{GM}{R^3}\left(\frac{1}{2}R\right)-\frac{G\left(\frac{1}{8}M\right)}{R^2}$$
Is this correct? Thanks
Recently viewed video about wormholes that required negative energy to create it. Suppose hypothetical aliens have discovered this technology. Spaceship enters in first point and exit at second. To prevent spaceship destruction they might have technology to smooth gravitational waves on exit...
Electromagnetic or gravitational wave carries energy and momentum from place to place as,I understand.Does it imply that such waves only can carry information and if their energy gets dissipated as heat, the information contained is lost.
Is this information content is to be decoded by human...
Hello everyone,
I know that GR equations are complicated and beyond my scope.
But does GR give a simple gravitational equation: Force (as we know it) as a function of distance? (without any complicated tensors).
- If yes. What is the equation? Does it give us something similar to Newtons...
I was wondering what someone standing far away from a planet with mass would see if he drops a clock towards the mass. And then vice versa if I was standing on the planet, what would I see. would I see the clock tick fast and then slow as it approaches?
Thanks!
How does the Earth's reference frame "know" to experience the gravitational pull of where the sun/Earth barycenter will be in 8 minutes, rather than orbit around the spot where the barycenter was 8 minutes ago? The latter case seems required by the finite speed of gravitation, but coplanar...
My attempt:
Let ##M_e## be the mass of the Earth and ##M_m## be the mass of the person. Let ##D_{EM}## be the distance from Earth to Mars and let ##R_e## be the radius of the earth.
Defining these constants (leaving off units for brevity):
Masses in Kilograms (G is not a mass but I'll leave...
It's a well known fact that acceleration due to gravity is independent of the mass of the accelerating body, and only depends on the mass of the body it is accelerating towards and the distance from it.
One can prove this mathematically very easily.
F=GMm/r^2 (equation 1)
but also F=ma...
An exact gravitational plane wave solution to Einstein's field equation has the line metric
$$\mathrm{d}s^2=-2\mathrm{d}u\mathrm{d}v+a^2(u)\mathrm{d}^2x+b^2(u)\mathrm{d}^2y.$$
I have calculated the non-vanishing Christoffel symbols and Ricci curvature components and used the vacuum Einstein...
Density of the Sphere = 3M/4πR³
Mass of carved out sphere
= density × 4π/3 × R³/8
= M/8
The position of center of mass of The Sphere
{M(0) - M/8(R/2)}/M-M/8
-R/14
So total distance between centers of the two bodies is R/14 + 3R = 43R/14
So now I found force between the Mass 7M/8 (left out...
Black holes form. An undeniable fact. Let's imagine a massive shell collapsing under its own weight (the exact composition of the mass is not important, so just imagine to be a continuous mass with zero thickness).
What happens if the process of collapse evolves? The time on the inside will run...
I haven't gotten anywhere. I don't find it possible to calculate this since Fg varies based on the Mass of the meteroide and because of that it will change acceleration. I thought about trying to remove m1 by making F=m*a the same as 𝜸(m1*m2)/r^2 since I think they are the same force.
m*a=...
A question to physicists: What sort of real world scenario / image would *best* depict the increase in gravitational potential energy in a radial field?
Would a rocket traveling through the Earth's atmosphere suffice or are there better alternatives?
This image would have to be relevant to the...
Book says that correct answer is d) but I can't understand why. If the result of gravitational and centrifugal force is 0N then there is no force that would keep those objects inside the spacecraft orbiting around the planet. Or am I just completely wrong?
Thank you for your help.
It seems to me that gravitational waves are ignored when inflationary physics are described. I'm not very well read, and honestly do not know so much about most of the physics going on with inflation. Still, wave mechanics matter, harmonics matter, and it just seems intuitive to me that in order...
Hi if I understand it correctly, this is the process to find freefall acceleration of a falling body.
S=ut+1/2at^2 Initial time and displacement is zero so,
S=1/2at^2 find acceleration
a=2(S/t^2)
graph for change in displacement over time squared
a= 2(yf-yi/xf-xi) (f=final i= initial)
I...
How do gravitational waves in spacetime stretch and compress solid matter such as the LIGO experiment. I ask this because the expansion of spacetime of the Universe doesn't seem to have any effect on the small scale ie the solar system.
i spoke to my proffesor about it but all he said was to put 1 in m1 and m2... for r^2 since it says to quadruple to just put 4^2
I asked about the G in the equation but he said not to worry about iit and pretend its not there...
Hi !
It catches my attention that atomic particles such as protons, neutornes, electrons and their respective subparticles such as Quarks are theoretically formed by high-energy electromagnetic fields such as gamma rays and then the gravitational field that would generate the mass of these...
Hi,
I would like to ask for some clarification about the physics involved in the gravitational waves detection using interferometers.
Starting from this thread Light speed and the LIGO experiment I'm aware of the two ends of an arm of the interferometer (e.g. LIGO) can be taken as the...
A popular theory is that black holes gradually leak information because of black hole evaporation due to hawking radiation. When black holes merge, a significant portion of their mass is converted into gravitational waves. If it's true that black holes leak information due to hawking radiation...
Here is my solution, which is correct.
The tilt of the water at the top can be described in terms of ##x## and ##y## as ##y = \frac{2y_0}{L}x##. The height of the water at any given x is then equal to ##h + \frac{2y_0}{L}x## where ##x \in [-\frac{L}{2}, \frac{L}{2}]##.
So the potential...
Alright, so I have a question. Now, on planets such as our Earth, there are a longitude and latitude as well as altitude. If I am not mistaken, I believe the latitude and altitude are part of what affects gravity, or weight, on a planet. Latitude makes it so that the object in question is...
As an object approaches a black hole’s event horizon, it experiences increasing gravitational time dilation, causing it to appear to an outside observer to slow down, until, at the event horizon, it appears to stop. An object traveling in space that increases its velocity from one...
I am reading 't Hooft introduction to general relativity.
https://webspace.science.uu.nl/~hooft10 ... l_2010.pdf
In this text 't Hoof derives the Rindler transformation.
A little bit further he writes
My question is, how does he come to that formula $$\rho^{-2}g(\zeta)$$
There is a formula for the potential ##\varphi## outside of a homogenous ellipsoid of density ##\mu## in Landau\begin{align*}
\varphi = -\pi \mu abck \int_{\xi}^{\infty} \left(1- \dfrac{x^2}{a^2 + s} + \dfrac{y^2}{b^2 + s} + \dfrac{z^2}{c^2+s} \right) \frac{ds}{R_s} \ \ \ (1)
\end{align*}where...
The full title of the publication is:
Rare Events Detected with a Bulk Acoustic Wave High Frequency Gravitational Wave Antenna
It is published in Physics Review Letters and reported in Phys Org.
They have created a small piezo-electric device (< 2cm, though it gets bigger once you create an...
If I'm standing on Earth, is my time dilation actually greater than if I was in a rocket accelerating at 9.8m/s^2 in deep space due to me being in a gravitational field on top of the acceleration? Geodesics experience time dilation in gravitational fields, so it seems like there is an additive...