Gravity Definition and 1000 Threads

I am unable to find a paper on this only the abstract, but it seems to be saying that there is no Dark Matter? The tightness of this relation is difficult to understand in terms of dark matter as it's currently understood, the researchers said. It also challenges the current understanding of...

Homework Statement Homework EquationsThe Attempt at a Solution I understand in general the argument of the problem, the only thing which I'm not sure of is why the gravity doesn't affect the torque. My guess is that it gets canceled by the normal force that is applied on the axle but I'm...

i am making a custom size card box filled with stuff that i want to put on top of a shelf (the box is bigger than the shelf), assuming the weight of the object is distributed evenly in the card box, what percentage of the box surface area (bottom of the box) that i need to have on the surface of...

Verlinde sought to reproduce the successes of other modified gravity theories in a variant of his entropy based gravity theories called "emergent gravity". Unfortunately, it doesn't reproduce the observed data. Federico Lelli, Stacy S. McGaugh, and James M. Schombert "Testing Verlinde's...

Gravitons are particles believed to be the cause of gravity but can anyone tell me their principle and how they work

Is it possible to find the speed increase due to gravity pull using the SR velocity addition formula or the calculator here? http://hyperphysics.phy-astr.gsu.edu/hbase/Relativ/einvel2.html Can you confirm that it is in accordance with GR formula? For example, if an asteroid is approaching the...

Why does the energy of a photon increase when falling into a gravitational field ? If we use the equation E=hf, then the energy of the photon increases, but I understand that we also need to add the potential energy to find the total energy. Et=Ep+hf. The potential energy decreases by the same...

Dear Forum, The title "Speed of time" is the best I can come up with. We know that time isn't constant, rather it depends on the speed at which we move as well as the gravity we are subjected to (see https://en.wikipedia.org/wiki/Gravitational_time_dilation for a reference to the latter). As a...

Hello. Say you have a uniform rod in free-fall. Would it rotate? Suppose you compute the rotation around the CM. I computed that the lever arm is the same on either side, regardless of the angle at which the rod falls, so there can't be any rotation. So if I just dropped a 30º to the horizontal...

I am not sure I can express clearly my thoughts on this one, but I am going to try. The effect of mass on space, and the resulting gravity, is sometimes described, in a two dimensions graphic, as a bowling ball applying pressure on the surface of a mattress, or something equivalent. Thus, the...

Recently watching a documentary about stars (how the universe works), I was wondering about two things. The first one is: how is it possible to have stars with such a wide range of sizes? As far as I understand, stars are created in swirling gas clouds, nebulae. When the accumulation of gas...

I have seen many examples of the EOM for a rocket derived for the following cases: No gravity, No drag Gravity, No drag No gravity, linear drag (b*v where b is a constant) I have never seen Gravity, linear drag Gravity, quadratic drag I took John Taylor's two examples of linear drag and...

If acceleration involves a change in velocity - dv/dt, what velocity is changing for an object at rest with gravitational force? Example - an apple on a table, mg down = the normal force ma up, but neither a nor g seem to involve a dv? the forces involved do not involve changing any...

I was cleaning up the kitchen, and there was a large pot that had been filled with water to soak in the sink. A rectangular nylon pot scrubber was hanging over the side of the pot, about 2/3 in the pot and 1/3 hanging out. As I ran the tap, the pot filled up and overflowed, but even after the...

How much progression has physics made in uniting QM and gravity? Have we made any steps to unite them? have we discovered anything remotely related to it?

Hello, Can anyone suggest some text(books/papers) for a better understanding of Tolman solution and the solution with f(R) corrections? I came across Tolman solution while studying exact solutions of Einstein's equations,first in "Lectures on General Relativity by A. Papapetrou" and later in...

In the experiment using pencils of light by Tolman, is has been shown that two parallel light beams do not attract but anti parallel beams do. What happens if we use different wavelengths for the light beams. Will the higher frequency beam be less deflected ?

The question is about a box with no movement standing on a hill. The hill has an angle of 25 degrees. The box has a mass of 40 kg. 1. Calculte the gravity This I still get: F= M x A = 40 x 9,81 = 3,9 x 10^2 The next question tough: 2. Calculate the component Fgravity,x off the gravity...

If mass increases with speed then what is the mass and speed of a particle falling from a large distance into a black hole or onto a neutron star?

Hello, Can anyone suggest some text(books/papers) for a better understanding of Tolman solution and the solution with f(R) corrections? Thanks PS: I hope i have posted this in the right section.

Gravity tends to make ordered structures of free particles. Does this mean that gravity is decreasing the entropy of these particles, or is there some compensating mechanisms in order to let the entropy increase (for example the emergence of gravity waves, though I doubt that's enough to compensate.

Homework Statement I do not know if this is the right forum to be asking this, but it is the best i have found. A classmate of mine came with the statement that if the Earth stopped spinning we would all float off to space because the Earth's mass is to small to able to hold everyone down. I...

(I suck at math... but I really like physics. In school, I flunked math on a regular basis and somehow managed to get decent physics grades... in spite of terrible math skills. But what I am good at is getting an image in my head of the physical properties of the universe and how it behaves.)...

Homework Statement A rocket with initial mass of m0. The engine that can burn gas at a rate defined by m(t)=m0-αt, and expel gas at speed (relative to the rocket) of u(t)=u0-βt. Here, m0, α, u0, and β are all constants. Assume the lift-off from ground is immediate a) The rocket speed v(t)=...

For example if you send a light beam towards a massive object the propagation speed will reduce if μ and ε are increasing, but the spacetime curvature will compensate for that reduction.

It is known that wavefronts of internal OAM photons travel slower than light but I wonder what happens if you accelerate such a beam. This should be possible under gravity.

If stars have finite mass, gravity, and density, why does a black hole have infinite density, mass, and gravity and why doesn't it attract everything around it with such infinite gravity? Also, with infinite density, why are black holes all different sizes?

What are the different approaches to solving quantum gravity that are in the framework of quantum field theory?

Imagine that we had discovered an habitable planet, Planet X, located 10 light years away from Earth, and that we had managed to establish a small colony there. Now imagine that because of a much stronger gravity than on Earth, time on Planet X would run 5 times slower than on Earth: 1 year on...

this paper https://arxiv.org/abs/1701.02311 Hypercuboidal renormalization in spin foam quantum gravity Benjamin Bahr, Sebastian Steinhaus (Submitted on 9 Jan 2017) In this article we apply background-independent renormalization group methods to spin foam quantum gravity. It is aimed at...

Based on my thinking if gravity was a constant wouldn't it be equally hard to walk up a hill versus walking on a flat surface or even going down? Too me it seems like the steeper the angle the more gravity and smaller angles would be less gravity. So it is pushing you against an angle.

If a space station has artificial gravity created by spinning, how can it best be spun up to speed? Little attitude rockets could do it, but they would use up fuel, and limit your ability to change the spin rate in future. What if you had an external wheel that you spin up very fast in the...

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...

Can it be either?

Are there any linear quantum gravity theories out there with respect to the wave function?

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?

PeterDonis submitted a new PF Insights post The Schwarzschild Geometry: Part 4 Continue reading the Original PF Insights Post.

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...