A 3D projection of an tesseract performing an ...
A 3D projection of an tesseract performing an isoclinic rotation. (Photo credit: Wikipedia)

I watched Interstellar last night. It’s rare that I don’t like any half-decent science fiction movie, so it gets a thumbs up, though it had its high- and low-points.

It would be difficult to get away with describing Interstellar as truly a “hard science” movie – but it makes quite a few nods in that direction, my favourite being its insistence that a worm hole, as an anomaly in three-dimensional space, should actually be a “worm sphere”.

The fundamental conceit of the film – that a hick farmer from the western US (or somewhere meant to look like the western US) was really a top quality pilot – was difficult to buy into while Michael Caine’s performance was universally dismal.

And, of course, the overall plot feels like an attempt to reimagine 2001: A Space Odyssey – which, despite being nearly 50 years old now, remains unsurpassed as filmic musing on humanity’s destiny in space.

In what sense do photons exist?

What Would Richard Feynman Do?
What Would Richard Feynman Do? (Photo credit: Maitri)

This is a genuine question on my part – and I would be grateful for any answers!

The inspiration for asking the question comes from Genius: Richard Feynman and Modern Physics – my current “listen while running” book – along with Feynman’s own description of radiation in QED – The Strange Theory of Light and Matter.

Feynman argues that there is no radiation without absorption: in other words a tree that falls in an empty forest does indeed make no sound (if we imagine the sound is transmitted by photons, that is).

This sounds like a gross violation of all common sense – how could a photon know when it leaves a radiating body that it is to be absorbed?

But then, general relativity comes to our rescue – because in the photon’s inertial frame the journey from radiator to absorber is instantaneous.

But how can a body that exists for no time at all, exist at all?

Then again my assumption in asking this question is that time is in some sense privileged as a dimension of spacetime. This is a pretty deep controversy in theoretical physics these days and I am not qualified to shed much light on it – but let us assume that a body can exist with a zero dimension in time but real dimensions in space, can we then have bodies which have zero dimensions in space but a real dimension in time? If so, what are they?


Thanks to @PootBlog but I still don’t get it

Magnets have many uses in toys. M-tic uses mag...
Image via Wikipedia

I have been on holiday with the family in a not exactly sunny, but still perfectly pleasant Bilbao, and so have not replied to this as soon as I probably should have.

But thanks to Damian Counsell (@PootBlog) who responded to my annoying twittering by explaining one of the magnetism issues I had:!/PootBlog/status/127842530271313920!/PootBlog/status/127842800975880192

I have to say, though, I am less than convinced. Say I create a new permanent magnet. How do other magnets know about it? In other words how does this “field” propagate? As it carries information it must surely propagate at the speed of light – but how? Is it a property of space-time itself?

It’s official: we’re getting bigger all the time says Nobel Committee

Prevailing model of the origin and expansion o...
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The decision to award this year’s Nobel Prize for Physics to three astrophysicists who, through measuring the brightness of distant supernovae showed that the expansion of the universe is accelerating, is simply the highest possible confirmation of what most if not all in the field have accepted for a decade or more.

That idea is a decisive break from the cosmology I was taught in 1987 – then the argument was whether the geometry of space time was circular (ie., the big bang would be followed by a big crunch as like a ball thrown in the air,eventually  everything fell back to the starting point), parabolic – ie., the expansion and mass were in exact balance and that at an infinite time in the future the expansion would halt – or hyperbolic, with the expansion too fast for gravity to eventually halt or reverse it.

What has been honoured today does not directly affect these three choices – presumably the expansion could accelerate and then slow and then reverse – but the theory seems pretty clear – the acceleration and the “dark energy” (code for “we don’t know”) that is causing it means the space-time will not stop expanding.

So, does this mean our universe is a “one shot deal” – began with the Big Bang and extending for ever? Not necessarily. Designing experiments to deduce what might have existed before the Big Bang is obviously very difficult (how can you find out what happened before time began?) but there are physical (as opposed to meta-physical) theories and arguments about observational evidence.

Roger Penrose‘s Cycles of Time has one theory (though I’ve not got that far yet) and I have seen Neil Turok on TV outline another (an aside: I don’t now Professor Turok, but I used to know his parents who were leading anti-apartheid activists and members of my local branch of the Labour Party – small world, very big universe).