What is spacetime curvature

This deformation occurs in four dimensions, so the two-dimensional bedsheet is a limited model. Try visualizing these depressions on all sides of a planet to build a more accurate image of this concept. When a smaller mass passes near a larger mass, it curves toward the larger mass because spacetime itself is curved toward the larger mass.

It can also mean a change in direction, like when you go round a roundabout, causing you to lean towards the side of the car. The cylinder is rotated faster and faster until the acceleration eases and the movement stays constant. But even once the speed is constant, you still feel the accelerated motion—you feel yourself being pinned to the outer edge of the ride. So if someone stood in the very centre of the ride perhaps held by a brace, stopping them from falling to the edge , they would notice all those weird effects we saw under special relativity—that those on the edge will contract in length, and their clocks will tick at a slower rate.

The equivalence principle tells us that the effects of gravity and acceleration are indistinguishable. In thinking about the example of the cylindrical ride, we see that accelerated motion can warp space and time. It is here that Einstein connected the dots to suggest that gravity is the warping of space and time. Gravity is the curvature of the universe, caused by massive bodies, which determines the path that objects travel. That curvature is dynamical, moving as those objects move.

To date, his predictions—as strange as they may sound—have all stood the test of time. Light travels through spacetime, which can be warped and curved—so light should dip and curve in the presence of massive objects. This effect was first observed in , analysing starlight during a solar eclipse. Astronomers found that starlight that passed very close to the sun was very slightly offset in position compared to the same starlight when measured at night.

Similar to how the passage of time is changed under special relativity, general relativity predicts that massive objects will also dilate time. The more massive the object, the more noticeable the effect. On board each satellite is an atomic clock, and your position on the planet can be determined by checking the time broadcast by the satellites above you and comparing those times against the known position of each satellite.

Both effects have been confirmed by a range of experiments , including the Gravity Probe B satellite. Equipped with extremely sensitive gyroscopes, this satellite measured the tiny twists and warps in spacetime made by Earth as it moves and rotates through space.

Since the curvature of spacetime is dynamical, moving objects should create ripples in space that permeate through the universe. Most of these ripples are too small to notice, but the more extreme the event, the higher the chance we can detect it. Imagine two very massive objects, such as black holes. If those objects were to collide, they could potentially create an extreme disturbance in the fabric of spacetime, moving outwards like the ripples in a pond.

But how far away could such waves be felt? Einstein predicted that gravitational waves existed, but believed they would be too small to detect by the time they reached us here on Earth.

So it was with great excitement that on February 11 , the scientific community was abuzz with the announcement that a gravitational wave GLOSSARY gravitational wave Ripples in spacetime that propagate outwards like waves had been detected. We needed instruments capable of detecting a signal one-ten-thousandth the diameter of a proton 10 meter. In the LIGO experiment, a laser is directed into a large tunnel structure. LISA Pathfinder performance analysis. LISA Pathfinder operating in space.

Also Available As. Also Available As x KB. Related Images. Related Videos. Related Publications. Newton's concept of the Universe was simple, straightforward, and philosophically dissatisfying to many.

He claimed that any two masses in the Universe, no matter where they were located or how far apart they were, would instantaneously attract one another via a mutual force known as gravity. The more massive each mass was, the greater the force, and farther away they were squared , the lesser the force. This would apply to all objects in the Universe, and Newton's Law of Universal Gravitation, unlike all the other alternatives put forth, agreed with observations precisely.

Newton's law of Universal Gravitation has been superseded by Einstein's general relativity, but But it introduced an idea that many top intellectuals of the day could not accept: the concept of action-at-a-distance. How could two objects located half-a-Universe away suddenly and instantly exert a force on one another?

How could they interact from so far away without anything intervening to mediate it? Descartes couldn't accept it, and instead formulated an alternative where there was a medium that gravity traveled through. Space is filled with a type of matter, he argued, and that as a mass moved through it, it displaced that matter and created vortices: an early version of the aether. This was the earliest in a long line of what would be called mechanical or kinetic theories of gravity.

In Descartes' vision of gravity, there was an aether permeating space, and only the displacement of This did not lead to an accurate formulation of gravity that matched with observations.

Descartes' conception, of course, was wrong. Agreement with experiment is what determines the utility of a physical theory, not our predispositions towards certain aesthetic criteria. When General Relativity came along, it changed the picture Newton's laws had painted for us in some fundamental ways.

For example:. Action-at-a-distance was here to stay, but Newton's "infinite-range force through static space" was replaced by spacetime curvature. The curvature of space means that clocks that are deeper into a gravitational well -- and hence, in If the Sun were to simply wink out of existence, disappearing from the Universe, we wouldn't know for some time.

Whether through a medium or in vacuum, every ripple that propagates has a propagation speed. In no