If you could travel back in time1/12/2024 ![]() This states that black holes can be characterised by three numbers – their mass, charge and angular momentum. In separate work, Hawking sparked the 'no hair' theorem of black holes. Hawking devised the second law of black holes, which states that the total surface area of a black hole will never get smaller. Their field is so intense that they form their own set of physical laws unlike anything else in the universe. They showed that Einstein's theory predicted a singularity in our distant past: The Big Bang. Up until the '70s physicists had known Einstein's theory allowed for 'singularities' - points where space-time appeared to be infinitely curved.īut it was unclear whether or not these singularities actually existed.īirkbeck College physicist Sir Roger Penrose showed that singularities do exist as they can form in black holes.Īlongside Sir Penrose, Hawking applied the same idea to the universe in its entirety in 1970. 'Space-time' is a theory used by physicists to describe the fusion of 3D space and time into a four-dimensional continuum. The objects are so powerful they bend time and space in bizarre ways, and in 1970 Hawking showed how black holes alter 'space-time'. One of Hawking's first key ideas was how space and time react within the brutal confines of black holes.īlack holes are regions of space with a gravitational field so intense that no matter or radiation can escape. Stephen Hawking, who sought to explain some of the most complicated questions of life while working under the shadow of a likely premature death, has died at 76 ![]() But we also need to produce regions of negative energy density to stabilise it, and the classical physics of the 19th century prevents this. The answer is maybe, and the warping we need is a traversable wormhole. So could we warp spacetime in just the right way to close it back on itself and travel back in time? If we squeeze in enough mass, spacetime becomes so warped that even light cannot escape its gravitational pull and a black hole is formed.Īnd if you were to approach the edge of the black hole – its event horizon – your clock would tick infinitely slowly relative to those far away from it. The more mass we squeeze into a region of space, the more spacetime is warped and the slower nearby clocks tick. WormholesĮinstein also told us that the force of gravity is a consequence of the way mass warps space and time. The law of causality would be violated and the concept of cause and effect would lose its meaning. Instead, it would no longer make sense to talk about forward and backward at all. But even if we could, time wouldn't simply run backwards. Unfortunately, it takes infinite energy to accelerate a human being to the speed of light, let alone beyond it. So what if we were to travel faster than light, would time run backwards as science fiction has taught us? If you were to move at the speed of light, you would appear frozen in time – as far as you were concerned, everyone else would be in fast forward. To everyone standing still, however, you will be in slow motion. The word 'relative' is key: time will seem to pass normally to you. The faster you move, the slower your clock ticks relative to ones you are moving past. Mathematically, our statement is equivalent to saying that Birmingham is about 125 miles from London.Īs physicists Brian Cox and Jeff Forshaw write in their book Why does E=mc²?, time and distance 'can be interchanged using something that has the currency of a speed'.Įinstein's intellectual leap was to suppose that the exchange rate from a time to a distance in spacetime is universal – and it is the speed of light.Įinstein also told us that the force of gravity is a consequence of the way mass warps space and time. What we mean is that the journey takes that long at an average speed of 50 miles per hour. Light speedĮinstein told us that space and time are parts of one thing – spacetime – and that we should be as willing to think about distances in time as we are distances in space.Īs odd as this might sound, we happily answer 'about two and half hours', when someone asks how far Birmingham is from London. Our inability to access the 'now' of someone far away is at the heart of Albert Einstein's theories of space and time. The signals carrying their voices and images travel incomprehensibly fast, but it still takes a finite time for those signals to reach us. But this is something we can never actually know. ![]() We take for granted the ability to call our friends and family wherever they are in the world to find out what they are up to right now. ![]() Let's start with our everyday experience. The late theoretical physicists Stephen Hawking was 'cautiously optimistic' on the subject of time travel, the researcher explains
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