Why does time appear to go fats when you’re asleep?

Does it? Generally this is not true, and most people are good at judging how many hours they’ve slept. Some can even tell themselves to wake up at a specific time and do so. Time perception can be distorted, though, and experiments show that estimates are generally good, but people tend to overestimate time passed during the early hours of sleep and underestimate during the later hours. Time estimation during dreaming are much more variable and some people claim to have dreamt a whole lifetime in one dream. However, the best experiments to test this come from those very rare people who can induce lucid dreams (knowing they are dreaming) at will, and then signal to experimenters to indicate what they are doing in the dream. When asked to count to 100 while dreaming or while awake, the times taken match closely. And when asked to estimate how long a dream event took, those estimates are accurate. So if time does go fast when you are asleep, you are unusual!

Could we exist on earth under a red giant star?

About five billion years from now, the sun’s usual source of nuclear energy will be depleted. It will begin to expand and cool significantly, becoming a ‘red giant’. Its outer layers will be thrown off into space. As the sun loses mass, its gravitational pull will weaken and the planets’ orbit will widen. We know that mercury and venus will not be able to outrun the expanding sun, and will be engulfed and incinerated.

Earth may just outrun the swelling red giant but its proximity, and the resulting rise in temperature, will probably destroy all life on Earth, and possibly the planet itself. However, there’s no reason that life could not survive on another planet (or moon) sufficiently far out from the sun, as long as it lies within the sun’s expanded ‘habitable zone’. Life could also survive on suitably hospitable planets around other Red Giants.

Why do people cheat?

Because they want to win the easy way. As competitive animals, we human beings constantly seek out opportunities to gain money, food and sex, or simply to look good. Doing all this the hard way requires expenditure of time,efforts and energy, so cheating can obviously be very tempting.

Evolutionary game theory has helped to explain how altruism can exist alongside cheating. Generally, cheats do well when they are rare, but less well when they are many and have fewer non-cheaters they can exploit. So groups tend towards an equilibrium, with few enough cheats that it’s not worth the cost of stopping them. Sadly, this basic biological principle means we are unlikely ever to be completely free of cheats.

What happens to the energy of light as it crosses the universe

Light coming from ever more distant galaxies has an ever-longer wavelength, or a ‘red shift’. According to physics, that should mean the photons of light have lost energy on their journey. Yet this overlooks the weird physics that kicks in on cosmic scales. In particular, it ignores the fact that the Universe – and thus the very fabric of space and time – is expanding. This literally stretches the light, increasing its apparent wavelength while leaving its energy unchanged. This explanation is still rejected by some, who argue it’s the cosmic expansion that’s an illusion, while the energy of light really does decrease through collisions with particles in its path. This so-called ‘tired light’ idea is intuitively much more appealing, and can be put to the test. For example, it predicts that distant objects will appear much fuzzier, as the higher-energy photons striking them will be scattered more violently. Yet images of distant galaxies show they’re relatively sharp. On the other hand, the cosmic expansion theory predicts that distant supernova explosions should appear slower than nearby ones, while tired light theory predicts no such stretching of time. Observations of supernovae have confirmed a cosmic ‘slow-mo’ effect – proving tired light wrong again.

HOW DO GRAVITONS ESCAPE FROM A BLACK HOLE?

In Einstein’s theory of General Relativity, the force of gravity around a black hole is described solely by the warping or curvature of ‘space-time’. However, many scientists believe we can also describe gravity, just like the other forces of nature, as the exchange of ‘virtual’ particles – in the same way that particles of light, photons, carry the electromagnetic force. Unfortunately there is, as yet, no such quantum theory of gravity that would describe how it works at this level, although we have some clues as to what it might look like. But crucially, these ‘virtual’ gravitational particles (called ‘gravitons’) aren’t bound by the normal rules of physics. They can pretty much do what they like, including travelling faster than light, as long as they do it before we notice them! Consequently, a black hole’s event horizon presents no barrier to gravitons and hence their communication with the outside Universe.