Is time real, or is it just an illusion? In our latest video, we meet Jim Al-Khalili, physicist and author of On Time, at the Royal Observatory Greenwich, the home of the Prime Meridian, to explore one of the deepest mysteries in science.

From space-time at the heart of Albert Einstein’s theory of relativity to the arrow of time, entropy and the origins of the universe, Al-Khalili explains why physicists remain divided over the true nature of time.

Could the past, present and future all exist at once? And is time travel really possible? Join us for a mind-bending journey through one of physics’ greatest puzzles.

Modern medicine has an impressive array of drugs in its arsenal. If you are unwell, there is a very good chance your doctor will prescribe a pill to get you back to health. What our medical system is less good at, however, is stopping medication.

Take antidepressants. The drugs aren’t effective for everyone, but they work well for some. Once the medication does its job, though, or the life circumstances that brought on depression grow easier – what then? We don’t yet have a good answer.

Because antidepressants are relatively safe drugs, they can often be dispensed for months or years on end, without much consideration about the long-term implications, as we discuss. But thousands of people struggle to stop taking them, with little help from doctors.

The problem starts long before doctors write out the prescription, though. Clinical trials are typically short-term, lasting only a matter of weeks, and there are few financial rewards or even resources for those who want to study long-term use or when medication should be stopped. This lack of evidence then informs clinical guidance – or rather, its absence.

Few industries want to help people stop using their products, but healthcare should

Antidepressants are just one example. The opioid crisis was spawned, in part, by a flippant attitude to prescribing drugs, and a failure to regulate how often physicians should review patients’ doses. Medications from beta-blockers to acid-reducing stomach drugs, though beneficial for heart or stomach issues in the short term, can cause serious long-term problems. When such issues do come up, physicians have a tendency to prescribe more medications to help combat any side effects – a problem known as a “prescription cascade”, which can be especially difficult for people managing health issues later in life.

Few industries are invested in getting people to stop using their products, but healthcare should be an exception. We need to pay attention to the problems that arise when people stop taking medication, and develop detailed guidance and support, so that when it is the right time to make a change, deprescribing is a valid option, too.

Picture the world 100 or 200 years from now. What are you imagining? Hotter temperatures, melting glaciers or alpine places without snow? With heatwaves happening across Europe this summer, it’s not that hard to visualise.

Now picture Europe in a deep freeze where temperatures hit -20°C in London. Both of these scenarios might be the future we’re heading for, thanks to climate change. And there’s an even more worrying indicator: while almost the entire planet has been warming, there’s one patch in the North Atlantic Ocean just south of Greenland where temperatures have been falling.

Scientists call it the “cold blob”, and some think it could be a warning that one of Earth’s most important climate systems is beginning to change and may soon hit a tipping point where climate change no longer happens gradually. If this system flips, it could have devastating consequences that change all of our lives as we know them.