Reskin Menu

What is the ‘twin paradox’?


Anon

According to Einstein’s theory of Special Relativity, time isn’t the same for everyone. For example, if we observe a clock moving at a constant speed relative to us, it appears to mark time slower than a clock remaining with us.  The time difference is only significant when you approach the speed of light.
Imagine a pair of twins, one of whom is an astronaut that travels to a distant star. The stay-at-home twin will see his brother age more slowly than him. You’d expect the space-faring twin to see the same happen to his Earth-bound counterpart since they’re moving at the same speed relative to one another. But if the twins are re-united, Einstein said that the space-faring twin will have aged less than the one on Earth, which is odd given that they’ve both performed identical journeys relative to each other.
Einstein’s prediction has been confirmed in experiments with atomic clocks, so what resolves this paradox? The answer lies in the fact that the twins don’t undertake identical journeys. To get back to Earth, the travelling twin experiences a force in order to slow down and reverse direction. The stay-at-home twin doesn’t, making their journeys fundamentally different. Not surprisingly, so are the relative travel times of the twins, thus one of them ages more.

Comments: 2

Twin paradox

Thu, 2012-04-19 14:02
einsteinagogo

Doesn't general relativity play a part as well, given that presumably the rocket is travelling far away from the gravitational pull of the earth?

Gravity over Velocity

Sat, 2012-04-21 09:19
M Paul Lloyd

It does and leaving the influence of Earths gravity behind would make a very small difference but not of any significane. You could equally say that moving away from the influence of the Sun's gravity would have some effect. Thing is very high relative velocities, especially near light speed, have a similar effect to those created by the gravity of a very massive object, but it would have to be something as massive as a Black Hole to have a significant effect.
Experiments conducted some forty years ago with very accurate clocks being flown in opposite directions around the Earth are thought to have proved the 'Twin Paradox' to be an actual effect although more recent studies suggest that this was within an acceptable margin of error and may not prove anything.
The truth is this is all very theoretical and we still don't understand very much about gravity and kinetic energy.

Q&A Tabs
Is time real or an illusion?

Diverse thinkers, from the ancient Greek philosophers through contemporary quantum cosmology and eternal inflation theory, have called time an illusion. For them, the perception of time passing...

Is swallowing your own phlegm harmful?

Phlegm is the mucous secretion of the respiratory passages. The cilia cells that line these passages are continually driving the phlegm upward to the throat, where it triggers the swallow reflex...

Can I get sunburnt through glass?

Ordinary glass absorbs 97 per cent of the UVB rays that cause sunburn and some skin cancers, and 37 per cent of the less harmful UVA radiation. This translates to a protection of about SPF30, so...

What is the record for the most languages spoken by one person?

It depends on how high (or low) you set the bar of fluency. Ziad Fazah, born in Liberia, brought up in Beirut and now living in Brazil, claims to be the world's greatest living polyglot, with a...

Why do we salivate before we vomit?

Vomiting is a deliberate response by the body that evolved as a purging mechanism to remove toxins or foreign bodies from the stomach and oesophagus. Since stomach contents are highly acidic,...

Is time real or an illusion?

Diverse thinkers, from the ancient Greek philosophers through contemporary quantum cosmology and eternal inflation theory, have called time an illusion. For them, the perception of time passing...

Why don't passenger seats on aircraft face backwards?

Air crash investigators have found that flight stewards in rear-facing seats have suffered less severe injuries in accidents than forward-facing passengers. This is because the energy from the...

Does Britain still lead the world in anything?

While Britons have pioneered all sorts of things from the steam engine and the computer to passenger jets and rugby football, we have dismally failed to maintain world dominance in much at all...

Why does time seem to go faster as we get older?

Most people agree that the years seem to pass at an ever-accelerating rate. That’s because traditions, anniversaries and celebrations gradually accumulate and merge, so that the difference...

Can I get sunburnt through glass?

Ordinary glass absorbs 97 per cent of the UVB rays that cause sunburn and some skin cancers, and 37 per cent of the less harmful UVA radiation. This translates to a protection of about SPF30, so...