The arrow of time began its journey at the Big Bang, and when the Universe eventually dies there will be no more future and no past. In the meantime, what is it that drives time ever onward?
Martha Henriques at the BBC: When Isaac Newton published his famous Principia in 1687, his three elegant laws of motion solved a lot of problems. Without them, we couldn’t have landed people on the Moon 282 years later. But these laws brought to physics a new problem, which wasn’t fully appreciated until centuries after Newton and still nags at cosmologists today. The issue is that Newton’s laws work about twice as well as we might expect them to. They describe the world we move through every day – the world of people, the hands that move around a clock and even the apocryphal fall of certain apples – but they also account perfectly well for a world in which people walk backwards, clocks tick back afternoon to morning, and fruit soars up from the ground to its tree-branch.
“The interesting feature of Newton’s laws, which wasn’t appreciated till much later, is that they don’t distinguish between the past and the future,” says the theoretical physicist and philosopher Sean Carroll, who discusses the nature of time in his latest book The Biggest Ideas in the Universe. “But the directionality to time is its most obvious feature, right? I have photographs of the past, I don’t have any photographs of the future.” The problem is not confined to the centuries-old theories of Newton. Virtually all of the cornerstone theories of physics since then have worked just as well going forward in time as they do backwards, says physicist Carlo Rovelli of the Center for Theoretical Physics in Marseille, France, and the author of books including The Order of Time.
“Starting from Newton, and then Maxwell’s theory of electromagnetism, then Einstein’s work, and then quantum mechanics, quantum field theory, general relativity, and even quantum gravity – there is no distinction between past and future,” Rovelli says. “Which came as a surprise, because the distinction is so evident to all of us. If you make a movie, it’s obvious which way is the future and which one is the past.” How does a clear direction of time emerge from these descriptions of the Universe, which all lack their own arrow of time? As Marina Cortês, an astrophysicist at the University of Lisbon, puts it: “There’s a lot of implications that start with taking seriously the question, ‘Why does time pass?'” Part of the answer lies at the Big Bang nearly 14 billion years ago. Another insight comes from the opposite extreme, in the Universe’s eventual death. More here.
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Honorary contributors to DesPardes: Adil Khan, Ajaz Ahmed, Anwar Abbas, Arif Mirza, Aziz Ahmed, Bawar Tawfik, Dr. Razzak Ladha, Dr. Syed M. Ali, G. R. Baloch, Hasham Saddique, Jamil Usman, Jawed Ahmed, Ishaq Saqi, Khalid Sharif, Majid Ahmed, Masroor Ali, Md. Ahmed, Md. Najibullah, Mushtaq Siddiqui,, Mustafa Jivanjee, Nusrat Jamshed, Shahbaz Ali, Shahid Hamza, Shahid Nayeem, Shareer Alam, Syed Ali Ammaar Jafrey, Syed Hamza Gilani, Shaheer Alam, Syed Hasan Javed, Syed M. Ali, Tahir Sohail, Usman Nazir