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Since antiquity, humans have envisioned various means of time travel into the future or the past. The concept has since become a staple of modern science fiction. In particular, the number of films that make use of time travel has increased significantly over the decades, while the real-world science has evolved right alongside them, moving from simple Newtonian mechanics and general relativity to quantum mechanics and the notion of a multiverse or more exotic alternatives like string theory.

But not all time-travel movies are created equal. Some make for fantastic entertainment, but the time travel makes no scientific or logical sense, while others might err in the opposite direction, sacrificing good storytelling in the interests of technical accuracy. That's why last fall, we gave you the Ars Guide to Time Travel in the Movies, co-written by yours truly and my spouse, physicist Sean Carroll of Johns Hopkins University. The aim was to help us all make better, more informed decisions when it comes to choosing our time travel movie fare—and have a bit of fun while doing so.

The guide was never meant to be an exhaustive/comprehensive list; rather, we selected films that represented many diverse approaches to time travel across multiple subgenres and decades. We then evaluated each one—grading on a curve—with regard to its overall entertainment value and scientific logic, with the final combined score determining a film's spot on the overall ranking. Does the time travel make logical sense? Second, is the physical mechanism of time travel somewhat realistic? And third, does the film use time travel in narratively interesting ways? So a movie like Looper, which makes absolutely no sense if you think about it too hard, gets points for weaving time paradoxes thoroughly into the fabric of the story.

Enlarge / A stack of 60 Starlink satellites launched in 2019. (credit: SpaceX / Flickr)

SpaceX began launching operational Starlink satellites five years ago this month. Since then, the company has been rapidly developing its constellation of broadband satellites in low-Earth orbit. SpaceX has now launched about 6,000 satellites with its Falcon 9 rocket and has delivered on its promise to provide fast Internet around the world. Today, the company is the largest satellite operator in the world by a factor of 10.

But is this massive enterprise to deliver Internet from space profitable?

According to a new report by Quilty Space, the answer is yes. Quilty built a model to assess Starlink's profitability. First, the researchers assessed revenue. The firm estimates this will grow to $6.6 billion in 2024, up from essentially zero just four years ago. In addition to rapidly growing its subscriber base of about 3 million, SpaceX has also managed to control costs. Based upon its model, therefore, Quilty estimates that Starlink's free cash flow from the business will be about $600 million this year.