The universe is a bubble, or an onion. Or a hall of mirrors, shaped like soccer ball. Space or spacetime?
But what about all those other dimensions? Thus, the seeming inconsistency of The universe is three-dimensional.
Flat or Curved? What I do want to talk about here is what it is that is supposed to be flat. Thus the seeming contradiction: Matter curves spacetime. The universe is flat is easily explained, too: spacetime is curved, and so is space; but on a large scale, space is overall flat. Finite or Infinite? The observed universe So one thing we know is what we cannot know: the universe we can observe has finite extension.
Being Mister Fantastic On visualizing a finite speed of light Under a Blood Red Sky On the afterglow of the big bang, and why the sky used to glow red Still to come: how do we know that the curvature of space is a fact of life; what would the world look like if space were very curved; what is the curvature and the size of the observable universe; and what the heck does the observable universe have to do with Dante. Sphere-and-plane image by Joe Doliner. Many thanks to Scientific American cosmology guru George Musser.
Get smart. Sign up for our email newsletter. Sign Up. Read More Previous. Support science journalism. Knowledge awaits. See Subscription Options Already a subscriber? Create Account See Subscription Options. Continue reading with a Scientific American subscription. Subscribe Now You may cancel at any time. But from your perspective, watching the ship pass by, the light is moving both up and down and to the side, with the ship.
The light travels a longer distance with each tick. The faster you travel through space, the slower you travel through time. But whose time is really slowed down? Is it the person on Earth, watching his friend zip past in her spaceship?
When she leaves, the spaceship accelerates away from Earth. When she returns, the spaceship decelerates to avoid a crash landing. In both leaving and returning, the spaceship changes its frame of reference GLOSSARY frame of reference The physical environment of an observer that involves their state of motion.
A person travelling in one car is in a different frame of reference than someone travelling in a car going a different speed or direction, or a pedestrian at the side of the road, or someone travelling overhead in a plane, etc. This breaks the symmetry of the situation, and when the spaceship lands back on Earth, our astronaut really will be younger than her Earthbound counterpart.
The faster you travel through space, the slower you travel through time, and vice versa. Another consequence of special relativity is that fast-moving objects appear to contract in size, in the direction of their motion.
This follows from the distortion of time—after all, you can measure the length of something by the amount of space something travels through time e.
Unlike the age differences that can arise from time dilation, there are no residual effects due to length contraction once the moving object and the observer are reunited. Imagine waking up in a spaceship, accelerating through space.
Is there any physical experiment you could do within the confines of your spaceship to tell whether you really were accelerating through space assuming there were no windows to look out from , or if, instead, you were inside a spaceship stationary on the surface of Earth?
Einstein said no—just as Galileo imagined the indistinguishability between a person inside a smooth-sailing ship confined without windows and a person on land, Einstein realised that the effects of acceleration and gravity were indistinguishable too. This is called the equivalence principle GLOSSARY equivalence principle The effects of being in a gravitational field are indistinguishable from the effects of being in an accelerated frame of reference.
Once Einstein had formulated the equivalence principle, gravity became less mysterious. He could apply his knowledge of acceleration to better understand gravity.
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 then provides a description of the dynamic interaction between matter and spacetime. ESA uses cookies to track visits to our website only, no personal information is collected. By continuing to use the site you are agreeing to our use of cookies.
OK Find out more about our cookie policy. Toggle navigation Toggle navigation. Toggle mission navigation. Missions Show All Missions. For example,the massive Sun curves spacetime around it, a curvature that reaches out to the edges of the solar system and beyond. The planets orbiting the Sun are not being pulled by the Sun; they are following the curved spacetime deformed by the Sun.
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