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I don't think the universe is infinite, but instead is in the form of the "surface" of a four-dimensional Euclidean hypersphere, so is finite. Nor do I think our universe is the only one: there may be other "bubbles" like ours in the wider cosmos, of which our universe is only one part. To say …

Is the universe infinite? Space and time are assumed to have begun at the big bang. So, if our universe is expanding, it would need infinite time to become infinite in extent. Yet current theory maintains a beginning 13.8 billion years ago.

You ask: Is the universe conscious? The answer depends on what is meant by "conscious". If the definition is an operational one, the question can be settled by observation and experiment. If not, well, you can play more or less interesting semantic games ( 29 June, p 38 ). I think the nominal -ness suffix …

Chanda Prescod-Weinstein comments on the idea that the arrow of time is linked to increasing entropy. What this approach seems to miss is that, while in most systems entropy will almost always increase, there is a very small chance that a system will become more orderly, with lower entropy, just as a result of random …

In your story about getting UK climate goals on track, economist Michael Pollitt mentions the need to reduce the weight and size of vehicles. Why would anyone who wants to protect the environment design an EV that weighs more than 2 tonnes, leading to increased energy demand and road damage( 22 June, p 10 )? …

Yes, carbon offsets for air travel don't work. I, for one, won't get on a plane until that changes. If we want to mitigate the worst effects of climate change, no one should be getting on aircraft. But people seem to feel entitled to fly to see threatened areas of the natural world for themselves …

You report that the boom in solar energy around the world has led to panels being installed on prime agricultural land. This is bad news, and there are many more sensible alternatives: most obviously barren desert land that can't grow food ( 6 July, p 10 ). Another option would be the roofs of buildings, …

Moheb Costandi writes that artificial intelligence can analyse the neuronal activity of movie watchers and identify which scenes they were observing. While this shows we can map commonality in brain activity for AIs to tap into, we lack the ability to capture the phenomenological quality of the "experience". For AIs to cross the divide into …

Recent talk of consciousness in various organisms has got me thinking. Rather than trying to investigate whether organism X has consciousness, surely a more ethical standpoint would be to assume by default that they are all conscious, so any investigation should be reversed. I suspect it would be hard to prove the absence of consciousness …

There are two problems with arguments in favour of Dyson spheres, massive structures that advanced alien species might build to capture all of a star's energy. First, long before a civilisation could build one, the issue of hydrogen fusion would have been solved and so abundant energy would be available. Second, if the aliens' star …