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.
Start din 7-dagers gratis prøveperiode på Magzter GOLD for å få tilgang til tusenvis av utvalgte premiumhistorier og 9000+ magasiner og aviser.
Allerede abonnent ? Logg på
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.
Allerede abonnent? Logg på
THE HUNGER GAME
Obesity is on the rise, but as we blame our unhealthy food-ridden environment and look to wonder drugs to get rid of unwanted fat, what role do our genetics play?
HOW THE UNIVERSE WILL END
A colossal supercollider now in the early stages of development may one day help us predict the ultimate fate of the Universe. With it, scientists will be trying to find a hidden instability built into the fabric of existence... an instability that could destroy everything
DARK ENERGY MIGHT BE ABOUT TO THROW A SPANNER IN THE WORKS
The most mysterious phenomenon in the Universe could be about to spring another surprise on us
TAKE-OFF AT LAST
AFTER A LONG WAIT, THE WORLD'S FIRST ZERO EMISSIONS AEROPLANES ARE FINALLY TAXIING TO REALITY. BUT ARE THEY THE SOLUTION WE NEED?
INSIDE THE 3D, NANOSCALE ATLAS THAT REVEALS A FRACTION OF THE HUMAN BRAIN
The map is now the highest-resolution picture of the human brain ever created
HOW THE LATEST DEVELOPMENT IN NUCLEAR FORENSICS MAY HELP CLEAN UP CHERNOBYL
Contrary to popular belief, radioactive material doesn't glow. But a team of nuclear forensics experts are working on a device to make it do just that. BBC Science Focus's Noa Leach meets the scientists behind the innovative device
MAJOR STUDY SHOWS HOW ULTRA-PROCESSED FOODS CHANGE YOUR LIFESPAN, IF YOU'RE NOT EATING YOUR VEG
While ultra-processed food is bad for your health, a decades-long study suggests it may not be as harmful as previously thought
ORIGIN OF EARTH'S 'SECOND MOON' DISCOVERED
Asteroid sampling mission will confirm whether moon-like Kamo'oalewa came from our Moon
INTERMITTENT FASTING AND CORRECTLY TIMED WORKOUTS ARE KEY TO FAT LOSS, SAYS STUDY
A new approach to dieting and exercise could help you lose weight and enhance your health
MASSIVE EXPLOSION SPOTTED ON MYSTERIOUS DEAD STAR
A satellite in the right place at the right time captured an important cosmic sight