Understanding Gravity: Are There “Up” and “Down” in Space?

Any object with mass distorts the space-time continuum, which we perceive as gravity pulling us “down” toward the object’s center.

Astronauts on the International Space Station (ISS) have long used the seemingly weightless space for fun — chasing their dinner through the air, playing tug-of-war and impersonating superheroes. But are there traditional “up” and “down” in space? Based on the experience of astronauts, it’s easy to imagine that the terms we usually use to define where we are, such as up and down or south and north, no longer apply once we leave Earth.

To some extent this is true, but we can still use our human perception of space and time to orient ourselves in the stars.

Just like on Earth, astronauts on the ISS are affected by gravity, one of the four fundamental forces in the universe. According to Sanjana, a nuclear astrophysicist at the University of Chicago
According to Curtis, the prevailing view among physicists is that the “down” direction is the direction in which gravity pulls you, and the “up” direction is the opposite direction. Astronauts’ weightlessness stems from the fact that the International Space Station and the people inside are both in free fall, pulled toward the center of the planet by the Earth’s gravity. The space station levitates because the speed of the space station and the centrifugal force it generates pushes it “up”, that is, away from Earth, roughly equal to the pull of gravity. This equilibrium is called a stable orbit.

“It’s one of the most exciting aspects of physics,” Curtis said. “We have a framework for describing and understanding things that aren’t intuitive or that we can’t perceive. ‘Up’ and ‘down’ may be vague terms, but in physics In science, you can always find a definition that works.”

Einstein described gravity as a warping of the fabric of space-time, and to illustrate the theory scientists often use a taut sheet as a simplified metaphor. If you put a bowling ball on top of the sheet, its mass will sink the center of the sheet. If you then add a marble, it will roll towards the bottom of that sink, being pulled by gravity.

Any object with mass bends the fabric of space-time. Therefore, there is hardly any place in the universe that is not affected by gravity, this conclusion comes from Jessica Esquivel, a particle physicist at Ferminational Laboratory. If you put another marble on the map (even on the edge), it will be pulled from multiple directions. “Anywhere in space, you feel the curvature of that sheet, and that’s the gravitational pull that’s causing the phenomenon,” she said.

In general, the more massive an object is, the deeper the bend it creates and the stronger the pull, but your distance also matters. Therefore, the planet you’re standing on — whether it’s Earth or Mars — always exerts the strongest gravitational pull on you. At the same time, the planets in our solar system are pulled toward the center of the sun. Even farther away, the supermassive black hole at the center of our galaxy is also pulling the entire solar system closer. Beyond galaxies, the greatest pull comes from the nearest galaxy clusters.

“You can zoom in and out and see different layers of the fabric of that space-time,” Esquivel said.

While gravity is a fundamental force, our understanding of it is far from complete. For example, scientists have yet to incorporate gravity into the Standard Model of particle physics because the dominant theory of gravity (Einstein’s general theory of relativity) has so far been incompatible with the Standard Model. While terms like “up” or “down” help us understand the universe, they can sometimes hinder our understanding of fundamental physics.

“One of the most difficult things about my work is trying to step out of these binary relationships and imagine a space without up, down, front, back, past, present. We have to engage with this beautiful fluidity,” Esquivel said. , which is really hard, but also one of the most fun parts of the job.”

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