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LETTER OF THE MONTH

Accessible cities, please

Your interesting article on future cities (July issue) praises the idea of 15-minute cities, where the idea is that all shopping and entertainment should be within a 15-minute walk or cycle trip. But wouldn’t this disadvantage a significant part of the population? Estimates for the UK show that by 2030, six million people over 65 will have a long-term illness or disability. These people cannot walk or cycle significant distances, and are unlikely to have the balance for an electric scooter. Without door-to-door transport, these people will be totally isolated.

And then there are builders, plumbers and electricians who bring their supplies and tools with them and can hardly walk or use a bicycle. And anyone relying upon a delivery of large items like sofas and electric goods needs delivery to the door. Cities have to accept that there is a fundamental need for door-to-door transport (which can be made electric) alongside cycling or walking, or the city will fail many of its residents.

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Past times

I was reading Dr Katie Mack’s article about the James Webb Space Telescope (June issue), and my question is, where does the past begin when it comes to travelling through space? For example, is Voyager’s location, 14 billion miles from Earth, still considered to be in the ‘now’ or our present time? If so, at what stage in its outward journey through space will it begin to enter into ‘the past’?

Tony Jackson, Cornwall

Is Voyager in the ‘now’ or in the past?

Everything we see is in our past! Currently, when we receive a signal from Voyager 1, we’re hearing from it as it was more than 21 hours in the past. And when we look at the Sun we’re seeing it as it was about eight minutes ago, and even if you look at something across the room you’re seeing it as it was several nanoseconds ago. In a cosmological sense, because of relativity, there’s no way to define ‘now’ that’s universal – it’s necessarily dependent on where you are and what you’re doing.

Dr Katie Mack, astrophysicist


Patrick Salmond snapped these noctilucent clouds

Noctilucent clouds

I just read Pete Lawrence’s article about noctilucent clouds (June issue). I thought you might be interested to see a couple of photos I took on a flight back from Mexico on Friday morning. Earlier in the flight we also saw the aurora borealis. Enjoy!

Patrick Salmond, via email


Can aliens see our future?

I was reading the article by Dr Katie Mack (June issue) about the new telescope that will enable us to peer back in time with more clarity, and it made me think. We are able to peer back in time to galaxies forming 10 billion years ago because inflation meant that parts of the Universe grew faster than light speed, meaning the light from earlier objects is still catching up with us. If that is correct, then surely there are possible life forms that are even further out from us looking back on us potentially billions of years in the past. This would mean that if they had the technology to send us information, they could tell us our future. Is that an accurate assumption or have I overlooked a fundamental restriction to that being possible?

Stuart Young, via email

It’s just a property of relativity in the Universe, not inflation or anything moving faster than light, that means that when we see distant objects, we’re seeing things as they were in the past. Relativity means that everything we see is in the past. Wherever you are, you’re getting an outdated view of what you’re seeing, because the light that was emitted from the thing you’re looking at takes time to reach you.

So by the time a signal reaches you, time has passed for whatever sent it, and your information is already out of date. That doesn’t give us any option for seeing the future.

Dr Katie Mack, astrophysicist


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