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 am curious to know if the gravitic field of a rotating, disk-shaped mass is denser along its ecliptic. I'm referring to rotating bodies such as stellar systems, galaxies, etc. I would like to know if a second mass, passing through the ecliptic, would experience a difference such as tidal...
Homework Statement
You have a space station in space far from any planets or stars in form of a hollow cylinder with inner radius R1 outer R2 length L and density Rho. On a symetric axis z are 2 astronauts, 1 at the middle and the second at distance H=2L from the center of the bottom of the...
I was just looking at list of solar system objects and was surprised to see that the surface gravity of Uranus is only 90% that of Earth's. I get it that the "surface" of a gas planet is further from that planet's core than is the case for Earth.
But does surface gravity really have any effect...
https://en.wikipedia.org/wiki/Hierarchy_problem
I understand that hierarchy problem is the large discrepancy between aspects of the weak force and gravity. But why? Why is the explanation, that gravity is simply a much weaker force not acceptable? Is it possible that gravity is just an...
Homework Statement
Hi guys, I'm struggling to figure out how the solution in the picture that I posted was able to get rid of their mg factors and then come up with a factor of k for x_1 in their eigenvalue equation. You can see that in the second equation of motion there is no k*x_1 but it...
Homework Statement
Scientists are planning to launch a rocket from the surface of the Earth into an orbit at a distance of 18000 km above the centre of the Earth. The radius of the Earth is 6400 km and it has mass 6.0x10^24 kg.
What is the minimum work done to move the 150kg mass of the rocket...
Asymptotic safety in quantum gravity is a local QFT. According to many people, local quantum field theories cannot be correct in terms of being a quantum gravity theory.
Lubos Motl outlines 4 reasons why they can't be right.
"Quantum gravity cannot be described as a local field theory in the...
I am not sure about how micro and macro spaces communicate information, but this paper seems to need it for gravity to emerge. The paper is far to advanced for me to understand completely
https://arxiv.org/pdf/1611.02269v2.pdf
It also seems that in this paper that gravity and space time...
On wikipedia, I found one of the objections to MWI.
"We cannot be sure that the universe is a quantum multiverse until we have a theory of everything and, in particular, a successful theory of quantum gravity.[73] If the final theory of everything is non-linear with respect to wavefunctions then...
Homework Statement
I learned how to deriving Maupertuis's principle from Hamilton's principle under conservative energy condition and feel this interesting.
But when trying to derive a particle's behavior in gravitivity field,stuck...
The direction of grativity is along ##x## axis,the particle...
https://arxiv.org/abs/1411.1935
This paper says LQG does not produce the Unruh effect effect, and therefore must be wrong. What do you guys think.
You can click into the PDF to see the entire paper.
Ok - I have qualified this question with the word stupid so please go gently with me. Imagine you are talking to a rather stupid child when answering please.
My question is about dark matter. Every time I do a search for "proof of dark matter", I get the same answer, which is that using the...
Homework Statement
There are a big object and an astronaut in space. How do we calculate the gravitational force between them. I enclose a photo. I have given the mass of an astronaut, the dimensions of this giant ring and density of the ring. There is also a mistake in the photo. The astronaut...
Homework Statement
Homework EquationsThe Attempt at a Solution
For part a) I got t=0.571 seconds
For part b) I got s=4.6m
But part c) is what I'm stuck on. If his centre of gravity has shifted lower by 50cm, is his time spent in the air greater?
Hi All,
Long time absentee from the forums hoping for some direction in my new research.
I've been tasked to look into the stages of motion of objects (dropped from various heights), hitting a body of water (of various depths) and eventually hitting the seabed (of various sediment types). I am...
We see in our solar system the planets orbiting the sun, but why doesn't with all of the other forces in play the perpendicular velocity seemingly not decrease(or does it?). And if the perpendicular velocity of the planets slow down would that result in static planets not moving around the sun?
Thanks to all of you for your kind attention to my questions. May I ask another?
If what we're calling dark matter interacts with visible matter via gravity, wouldn't it be concentrated along these arms if density waves are a feature of gravitational force?
I'm only an interested layman so please forgive my lack of knowledge but assuming the universe is flat, infinite and the cosmological principle holds then why wouldn't the attractive force between galaxies cancel out?
If I think of a 2d analogy such as the surface of a sphere, and there were...
Thought experiment: Assume two galaxies in a galaxy group, initially at rest (with respect to one another). The distance between the centers of the galaxies is r = 1 Mpc.
The total mass of each galaxy is mg = 6 ∙ 1042 kg (including dark matter). This is ≈ 3 ∙ 1012 solar masses.
The...
I am totally confused. What is concerning the anisotropy the difference between re-entering gravity waves and re-entering density perturbations and more important for me what is then happening in the photon-baryon plasma between end of inflation and these re-enterings.
So there's a spaceship 5 light years away from Earth and they want to send a signal to Earth but a cloud of interestellar dust don't let them use light or radio signals so they decide to send a gravity signal.
So they produce a violent huge thermonuclear explosion that will send some particles...
I was sitting at my bed when I suddenly have an idea.
The unification of electromagnetism and gravity was made with General Relativity. For this to happen, one just need to write the energy due to electromagnetic field in "differential geometry" form, through the Electromagnetic tensor, in a...
If my understanding is correct, all particles are sources of gravitational fields (albeit minor ones), and the gravitational potential energy between two bodies is given by:
U = -GMm/r
So, if we have two Z bosons (or any other bosons with mass but no repulsion due to charge) which are traveling...
Dears,
In the film the Arrival, of Denis Villeneuve, the alien ship apparently subjugates the terrestrial gravity. It's one thing to simulate gravity in space, another thing would be to simulate a gravitational system apart on Earth. Is there at least a theoretical possibility for this? How...
Assume the universe is flat and neither expanding nor contracting whatsoever, and the only matter in it are two marbles separated from each other by a distance of 10 million light years. Would the marbles eventually begin pulling toward each other (after 10 million years)?
I understand that General Relativity can make a difference between a spinning and non spinning mass thus can make better prediction for planetary orbits for example. The effect is frame dragging.
However if we simulate a Newtonian gravitation and instead of representing a planet as a sphere...
1) If the idea that gravity is a curvature of space that causes objects to move towards each other then would it be appropriate to say that magnets do the same thing to space?
2) Does it seem a bit coincidental that both gravity and magnetism operate by the inverse square law or is it possible...
Suppose you have a perfect spring. By that I mean a spring that experiences no friction whatsoever, even internal, and that there is no elastic limit. Thus it obeys Hooke's law perfectly. Its own weight is negligible, and there is a point mass attached to the end of the spring.
Now, the spring...
I ever read that there is no meaning for quantizing fluid mechanics. While left hand side of Einstein field equation used fluid-like approximation for matter (momentum-energy tensor). Therefore, if the first statement is correct then there is no meaning for quantizing gravity, right?
Homework Statement
A baseball is thrown straight up with a speed of 25 m/s. Determine:
(a) The maximum height reached by the ball
(b) How long it takes the ball to reach its maximum height
(c)The time it takes for the ball to reach a velocity of 5m/s (down)
(d) The speed of the ball when it...
Hello all!
Lately i have been looking at many rocket equations, and i was wondering about the gravity loss on a rocket launch. I found the formula for the gravity loss
where g is of course the gravitational acceleration, and y is the flight path angle, but can somone explane why it looks like...
I recently came across an example of a fictional 2 dimension being and how that being would experience 3 dimensional interaction. In this is example the 2d being was on a pool table and would only see flashes of the pool balls as they interact with the 2d plane.
Is gravity similar; however, a...
Going through several definitions, it appears that escape velocity is equal to the potential energy. That is:$$\frac{1}{2}m v^2=-\frac{G M m}{r}$$but if I solve for velocity, $v$, I get:$$v=\sqrt{-2\frac{G M}{r}}$$So how do I get an escape velocity that isn't imaginary?
I'm trying to understand potential energy, especially with regard to gravity. There's a double negative that's difficult to grasp: The direction of the force is negative because the vector points radially outward and the force of gravity is directed inward, and the work done to bring an object...
In Schutz says When we have weak gravitaional fields then the line element *ds* is
$$
ds^{2}=-(1+2\phi)dt^{2}+(1-2\phi)(dx^{2}+dy^{2}+dz^{2})
$$
so the metric is
$$
{g_{\alpha\beta}} =\eta_{\alpha\beta}+h_{\alpha\beta}= \left( \begin{array}{cccc}
-(1+2\phi) & 0 & 0 & 0\\
0 & (1-2\phi) & 0 &...
For my physics assignment we have to design and test a way to allow an egg to fall from a three storey building and not crack. The only requirments are the egg must be visible in atleast one place and the smallest design wins. I tried making a crumple area and then protecting the egg with...
If a ship could cancel out the effect of gravity, wouldn't it be able to pass through the event horizon of a black hole, and take a tour of the singularity, and then just report back with its observations?
Also, if a ship had the capability to cancel out the effect of gravity, wouldn't this...
Propose an experiment:
Simultaneous test of matter warping space (Gravity) and quantum entanglement "spooky action" at a distance where the spin of the other particle instantly changes to clock or counter clock.
Will the result be that both Symmetric Changes are instantaneous?
Or will it...
Here's what my prof says:
"Define F_{mean} to be the mean force, F_close to be the force on the side of the Earth closer to the moon, and F_far to be the force on the side of the Earth furthest away from the moon.
On the closer side the net force is F_close - F_mean > 0
On the further side the...
Some time ago I tried to define classical inverse-square gravity on a 3-dimensional (cubical) torus T3: the quotient space obtained by identifying opposite faces of a unit cube. (Or more rigorously, the quotient space
T3 = R3/Z3
of R3 by its subgroup Z3 of integer points.)
I assumed there...
Is the theory that inflatons become dominate when gravity is strong (as in right after the big band) and when gravity is weak (as in driving the current expansion of the observable universe)?
Homework Statement
A horizontal pole is made of 8 pieces, 1 meter apart each. Forces that do not act at the ends are shown in the picture.
The pole does not rotate, and weighs 20N.
a. What is the sum of forces applied on the pole?
b. Where is it applied?
c. What are the forces at the ends...
Homework Statement
I searched around and found a manual, so this time I have the complete question in English (I'll use different numbers though, because mine is the 8th edition, and the manual is from the 14th, but it's not something that affects this exercise):
2.98) An alert hiker sees a...