Free fall in curved spacetime


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Warped time model in ReleQuant
The Leaning Tower at the Gravity Discovery Centre illustrates how time and gravity are linked. This screenshot comes from the Viten program General Relativity.

Free fall in curved spacetime

How can we visualise gravity in relativity? With a rubber sheet and marbles, maybe? My latest article in Physics Education presents a new model that illustrates how warped time gives rise to gravity.

Rubber sheet model in ReleQuant
The rubber sheet model illustrates how mass curves spacetime. This screenshot comes from the Viten program General Relativity.

Einstein’s general theory of relativity is our cur­rent best description of gravity. According to Einstein, gravity is a manifestation of the weird geometry of our universe: the mass and energy content in the universe shape the very fabric of space and time. Spacetime curves and bends and ripples under the influence of massive objects.

To illustrate this dynamic interplay, physicists often compare spacetime to a rubber sheet on which marbles circle around a central mass — a miniature model of the solar system held together by gravity. Yet, while the rubber sheet model uses curved space to explain planetary movement in an intui­tive way, the model ignores deformations in time.

Warped time pulls us down to the ground

In fact, these temporal deformations are the reason that we feel gravity pulling us down to the centre of the earth: Even though our planet curves both space and time around it, its mass is not large enough to curve space considerably. We experience gravity on earth mainly because of warped time. Which sounds pretty much like science fiction, right?!

My ReleQuant colleagues and I set about to develop a new model that would illustrate how warped time gives rise to gravity. Our interactive warped­ time model is part of General Relativity, a digital learning environment on the learning platform Viten hosted by the Norwegian Centre for Science Education.

Educating and engaging high school students

What is really cool about this warped time model is that it pools experi­ence from two educational projects - the Norwegian ReleQuant and the Australian Einstein-First projects - and that it takes a digital version of the Leaning Tower at the Gravity Discovery Centre as a setting to explore the movement of falling objects in curved spacetime.

In my latest paper, that recently got published in Physics Education, I explain how physics educators can educate and engage high school students in topics of relativity by finding suitable models that visualise gravity as the geometry of curved spacetime. You might want to give the warped time model a try yourself?

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