absorbed by stars tens of billions of years hence, contributing an infinitesimal nudge to drive their nuclear processes from extinction back towards birth.
Chen’s announcement of success was met with virtually unanimous scepticism — and rightly so, since he refused to divulge the coordinates of his discovery. I’ve seen the recording of his one and only press conference.
‘What would happen if you pointed an uncharged detector at this thing?’ asked one puzzled journalist.
‘You can’t.’
‘What do you mean, you can’t?’
‘Suppose you point a detector at an ordinary light source. Unless the detector’s not working, it will end up charged. It’s no use declaring: I am going to expose this detector to light, and it will end up uncharged. That’s ludicrous; it simply won’t happen.’
‘Yes, but—’
‘Now time-reverse the whole situation. If you’re going to point a detector at a time-reversed light source, it will be charged beforehand.’
‘But if you discharge the whole thing thoroughly, before exposing it, and then . . .’
‘I’m sorry. You won’t. You can’t.’
Shortly afterwards, Chen retired into self-imposed obscurity — but his work had been government funded, and he’d complied with the rigorous auditing requirements, so copies of all his notes existed in various archives. It was almost five years before anyone bothered to exhume them — new theoretical work having made his claims more fashionable — but once the coordinates were finally made public, it took only days for a dozen groups to confirm the original results.
Most of the astronomers involved dropped the matter there and then — but three people pressed on, to the logical conclusion:
Suppose an asteroid, a few hundred billion kilometres away, happened to block the line of sight between Earth and Chen’s galaxy. In the galaxy’s time frame, there’d be a delay of half an hour or so before this occultation could be seen in near-Earth orbit — before the last photons to make it past the asteroid arrived. Our time frame runs the other way, though; for us, the ‘delay’ would be negative. We might think of the detector, not the galaxy, as the source of the photons — but it would still have to stop emitting them half an hour before the asteroid crossed the line of sight, in order to emit them only when they’d have a clear path all the way to their destination. Cause and effect; the detector has to have a reason to lose charge and emit photons — even if that reason lies in the future.
Replace the uncontrollable — and unlikely — asteroid with a simple electronic shutter. Fold up the line of sight with mirrors, shrinking the experiment down to more manageable dimensions — and allowing you to place the shutter and detector virtually side by side. Flash a torch at yourself in a mirror, and you get a signal from the past; do the same with the light from Chen’s galaxy, and the signal comes from the future.
Hazzard, Capaldi and Wu arranged a pair of space-borne mirrors, a few thousand kilometres apart. With multiple reflections, they achieved an optical path length of over two light seconds. At one end of this ‘delay’ they placed a telescope, aimed at Chen’s galaxy; at the other end they placed a detector. (‘The other end’ optically speaking — physically, it was housed in the very same satellite as the telescope.) In their first experiments, the telescope was fitted with a shutter triggered by the
‘unpredictable’ decay of a small sample of a radioactive isotope.
The sequence of the shutter’s opening and closing and the detector’s rate of discharge were logged by a computer. The two sets of data were compared — and the patterns, unsurprisingly, matched. Except, of course, that the detector began discharging two seconds before the shutter opened, and ceased discharging two seconds before it closed.
So, they replaced the isotope trigger with a manual control, and took
Chen’s announcement of success was met with virtually unanimous scepticism — and rightly so, since he refused to divulge the coordinates of his discovery. I’ve seen the recording of his one and only press conference.
‘What would happen if you pointed an uncharged detector at this thing?’ asked one puzzled journalist.
‘You can’t.’
‘What do you mean, you can’t?’
‘Suppose you point a detector at an ordinary light source. Unless the detector’s not working, it will end up charged. It’s no use declaring: I am going to expose this detector to light, and it will end up uncharged. That’s ludicrous; it simply won’t happen.’
‘Yes, but—’
‘Now time-reverse the whole situation. If you’re going to point a detector at a time-reversed light source, it will be charged beforehand.’
‘But if you discharge the whole thing thoroughly, before exposing it, and then . . .’
‘I’m sorry. You won’t. You can’t.’
Shortly afterwards, Chen retired into self-imposed obscurity — but his work had been government funded, and he’d complied with the rigorous auditing requirements, so copies of all his notes existed in various archives. It was almost five years before anyone bothered to exhume them — new theoretical work having made his claims more fashionable — but once the coordinates were finally made public, it took only days for a dozen groups to confirm the original results.
Most of the astronomers involved dropped the matter there and then — but three people pressed on, to the logical conclusion:
Suppose an asteroid, a few hundred billion kilometres away, happened to block the line of sight between Earth and Chen’s galaxy. In the galaxy’s time frame, there’d be a delay of half an hour or so before this occultation could be seen in near-Earth orbit — before the last photons to make it past the asteroid arrived. Our time frame runs the other way, though; for us, the ‘delay’ would be negative. We might think of the detector, not the galaxy, as the source of the photons — but it would still have to stop emitting them half an hour before the asteroid crossed the line of sight, in order to emit them only when they’d have a clear path all the way to their destination. Cause and effect; the detector has to have a reason to lose charge and emit photons — even if that reason lies in the future.
Replace the uncontrollable — and unlikely — asteroid with a simple electronic shutter. Fold up the line of sight with mirrors, shrinking the experiment down to more manageable dimensions — and allowing you to place the shutter and detector virtually side by side. Flash a torch at yourself in a mirror, and you get a signal from the past; do the same with the light from Chen’s galaxy, and the signal comes from the future.
Hazzard, Capaldi and Wu arranged a pair of space-borne mirrors, a few thousand kilometres apart. With multiple reflections, they achieved an optical path length of over two light seconds. At one end of this ‘delay’ they placed a telescope, aimed at Chen’s galaxy; at the other end they placed a detector. (‘The other end’ optically speaking — physically, it was housed in the very same satellite as the telescope.) In their first experiments, the telescope was fitted with a shutter triggered by the
‘unpredictable’ decay of a small sample of a radioactive isotope.
The sequence of the shutter’s opening and closing and the detector’s rate of discharge were logged by a computer. The two sets of data were compared — and the patterns, unsurprisingly, matched. Except, of course, that the detector began discharging two seconds before the shutter opened, and ceased discharging two seconds before it closed.
So, they replaced the isotope trigger with a manual control, and took