According to first Newton, then Einstein, and now an experiment at CERN, gravity is an attractive force that exists between all objects in the Universe. That includes objects that have no mass, because gravity acts on energy, and mass is just one form of energy (as Einstein's most famous equation states, energy is equal to mass multiplied by the square of the speed of light). This is why even massless photons of light, travelling from distant stars, have their paths bent as they pass massive galaxies on the way.
Antigravity is a hypothetical repulsive gravitational force. In some ways, it sounds obvious that it should exist. There are both attractive and repulsive electric forces, so why not the same for gravity?
The difference is that electric charge comes in two types, positive and negative. Different charges (a positive and a negative) will attract each other, while charges that are alike (two positives or two negatives) repel each other. The equivalent of 'charge' for gravity is energy, and it only comes in one type: positive.
As these positive energies attract each other there doesn't seem to be room for antigravity, which is a pity because it would be a great way of flying around without the need for rockets, jet engines or even wings.
However, there is (or was, until this month) a possible get-out clause for antigravity: antimatter.
Antimatter isn't hypothetical, it's very real. Particles such as electrons have an antimatter equivalent.
The antiparticle of the electron is the positron, and it has not only been observed, but is regularly used in hospitals for diagnostic purposes.
Denne historien er fra November 2023-utgaven av BBC Science Focus.
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Denne historien er fra November 2023-utgaven av BBC Science Focus.
Start din 7-dagers gratis prøveperiode på Magzter GOLD for å få tilgang til tusenvis av utvalgte premiumhistorier og 9000+ magasiner og aviser.
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COULD MARINE CLOUD BRIGHTENING HELP US FIGHT CLIMATE CHANGE?
The theory behind marine cloud brightening is that brighter or whiter clouds reflect more sunlight back into space.
IS IT SAFE TO RUN EVERY DAY, OR SHOULD I DITCH MY RUN STREAK TO SAVE MY KNEES?
A running streak, where you run every day without taking rest days, can be highly motivating and beneficial for overall fitness. Running is great cardiovascular exercise and isn't to be discouraged (and finding a routine with some consistency is great). Getting a bit of exercise as often as possible is also hugely beneficial for your mental health.
WHAT MAKES THE MEDITERRANEAN DIET SO GOOD FOR US?
The Mediterranean diet may help you live longer, especially if you also adopt the lifestyle of people living near the Med during the 1950s.
WHAT IS MEXICO'S BLUE HOLE?
The world's deepest blue hole (marine sinkhole) lies off the coast of Mexico's Yucatán Peninsula. It's at least 420m (1,378ft) deep, but explorers still haven't found its bottom.
HOW CAN I TELL IF I'VE GOT HIGH CORTISOL LEVELS?
Cortisol is a hormone produced by glands in our bodies called the adrenal glands, which sit above the kidneys. It plays a critical role in various bodily functions, including regulating metabolism, reducing inflammation and helping the body respond to stress. While essential for our health, chronic elevation of cortisol levels can lead to several issues.
THE LUNGFISH
In 1836, European scientists discovered a peculiar animal from the River Amazon that they struggled to identify. Its eel-like body was a few feet long and its air-filled lungs persuaded anatomists it must be a reptile.
ARE WE THE ONLY SPECIES TO HAVE BEEN THROUGH A STONE AGE?
The Stone Age might conjure up images of early humans, sitting around a campfire or hunting prehistoric beasts, but evidence shows that we're not the only species that has learned how to work with stone tools. Wild chimpanzees (Pan troglodytes) use stone tools to crack open nuts.
Should we scrap daylight saving time?
Most of us look forward to the extra hour we get in bed every October, but researchers argue that changing the clocks twice a year harms our health
THE INTERNET OF ANIMALS
SCIENTISTS ARE USING ELECTRONIC TAGS AND SATELLITES TO TRACK WILD ANIMALS AND CREATE A DATA NETWORK THAT COULD HELP US ADDRESS THE BIODIVERSITY CRISIS
MUSIC FOR A DISTRACTED GENERATION
The number of things competing for our attention is often overwhelming. Can dreamy soundscapes created with neuroscience help our bewildered brains to concentrate?
