Article Why is there no such thing as antigravity?

[C C]

https://bigthink.com/starts-with-a-bang/...tigravity/

KEY POINTS: In Newton’s gravity, all masses attracted one another; there is no “negative mass” to repel. In Einstein’s general relativity, matter and energy curve spacetime, and curved spacetime is experienced as gravity. If there were negative mass, or even some sort of negative energy, you might imagine that spacetime could “curve” in the opposite fashion, resulting in antigravity. But this doesn’t describe our Universe. This is a profound fact, and makes gravitation very different from other forces, like electromagnetism, that have both attractive and repulsive features. So why can’t there be any “antigravitation” in our Universe?

EXCERPT: The big question that we need to consider is why gravity can’t work in a repulsive fashion as well: things only gravitate; they don’t seem to anti-gravitate. It’s as though space can only “curve” in one direction: the direction that makes things attractive, not repulsive. In the “2D bedsheet” analogy, matter and energy only ever cause space to curve “down,” never “up,” and so there’s only attraction, not repulsion. In the “3D grid” analogy, matter and energy only ever cause those lines to be drawn “inward,” never “outward,” and again, there’s only attraction, not repulsion.

There’s a profound and important reason for this that gets straight to the heart of what makes gravitation not only remarkable, but unique, among the four fundamental forces: there’s only one “sign” for the type of gravitational “charge” in the Universe: a positive one... (MORE - missing details)

[Syne]

It's not a coincidence that both gravity and time are unidirectional.

[stryder]

What tends to get me is that people talk about mass warping spacetime to create a gravitation well that's attract other bodies to it. 

It however neglects to consider how Lagrangian points exist, as the points themselves do not contain mass to warp spacetime, instead you have a correlation effect caused by multiple gravitation masses combining there localised effects to create a gravitational well homeostasis.

Lagrangian points of course can collect free floating matter which in turn would build up to increase the overall mass at that location (which in turn further changes the magnitude of effect on other gravitational bodies.)  .

So it actually begs the question:  Does mass warp spacetime or does warped spacetime create mass?


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On the subject of Why does Gravity seem to only attract? 

It's to do with amplitude and weirdly it actually suggests it's not attraction at all, it's actually repulsion.  If a force is exerted in one wave length, it doesn't necessarily inverse the wave to exactly the same dimension, the wavelength can translate its dimensions different thanks to direction (similar to angular momentum).  This is what leads to energy loss while still following the law of energy conservation. 

A simple (linear) analogy would be to have a Large ship and a small boat in the sea. The sea has waves that reflect from the vessels hulls concentrically.

Due to the difference in the area of the vessels, the concentric circles are different in size per vessel which effects the rebounding wave length. (They are short for the ship compared to the waves from the sea, and the boats are even shorter.

When the Ship and the boats waves head towards each other, the smaller waves fit within the amplitude of the larger waves. the smaller waves ripple across the larger waves in the opposite direction. The boats smaller waves however do not reach as far out as the ships longer waves.

  So you have to competing forces, however due to one changing it's level of state, they aren't seen to cancel each other out.  In fact one is stronger than the other, so there doesn't appear to be a counter force.

In this instance the heightened state of amplitude in the smallest waves is actually move energetic than the larger ones.

Since the wave coming from the Ship can reach a greater distance, there is a point where those larger waves are reflected by the boat, Which then creates further amplitude of smaller waves back in the inverse direction. This is why it appears that Large bodies attract smaller, ones however it's not actually due to a to attraction but a reduction ism of repulsion.

[Magical Realist]

Each dimension can only curve towards the next higher dimension positively. Since gravity is the curvature of 3D space towards time, that's always in the same direction, namely inward. Unless you wanna posit negative dimensions..But that's beyond my pay grade. lol

[Zinjanthropos]

Need to wrap my head around a couple things first. How did gravitational waves distort space time at BB if there wasn't anything to start with? (did space and time expand faster than C at creation?) And do gravitational waves (ripples in space time) intersect or bump into one another at times? If they do what happens, does one absorb the other and become greater? If so would two identical ripples from opposite directions cancel each other out? Would gravitational waves be stronger if space was contracting?

[confused2]

My take on Spacetime and nothing.
Consider the Earth and Moon.
The spacetime at the surface of the Earth is curved by the mass below it. The spacetime 1 yard above is curved (but slightly less) because it has to join up with the spacetime below it and also the flatter spacetime further away from the Earth.. (probably) all the way out to infinity. The Moon sits in the curved spacetime caused by the Earth and does the same thing of curving spacetime in the same way. If the Moon didn't curve spacetime then the Moon would be attracted to the Earth but the Earth wouldn't be attracted to the Moon. Things with no mass are attracted to the Earth but the Earth isn't attracted to them. Probably.
Spacetime doesn't actually exist except as a mathematical construct which enables us to make predictions.