Albert Einstein, one of the greatest minds of the 20th century, forever changed the
landscape of science by introducing revolutionary concepts that shook our
understanding of the physical world.

One of
Einstein's most defining qualities was his remarkable ability to conceptualize
complex scientific ideas by imagining real-life scenarios. He called these
scenarios "Gedanken experiments", which is German for "thought
experiments".

Image Credit: The scientific monthly/wikimedia

Here are a
few thought experiments that demonstrate some of Einstein's most
ground-breaking discoveries.

**Imagine you're chasing a beam of a light.**

This is
something Einstein started thinking about when he was just 16 years old. What
would happen if you chased a beam of light as it moved through space?

If you could
somehow catch up to the light, Einstein reasoned, you would be able to observe
the light frozen in space. But light can't be frozen in space, otherwise it
would cease to be light.

Eventually
Einstein realized that light cannot be slowed down and must always be moving
away from him at the speed of light. Therefore something else had to change.
Einstein eventually realized that time itself had to change, which laid the
groundwork for his special theory of relativity.

**Imagine you're standing on a train.**

Imagine
you're standing on a train while your friend is standing outside the train,
watching it pass by. If lightning struck on both ends of the train, your friend
would see both bolts of lightning strike at the same time.

But on the
train, you are closer to the bolt of lightning that the train is moving toward.
So you see this lightning first because the light has a shorter distance to
travel.

This thought
experiment showed that time moves differently for someone moving than for
someone standing still, cementing Einstein's belief that time and space are
relative and simultaneity doesn't exist. This is a cornerstone in Einstein's
special theory of relativity.

**Imagine you have a twin in a rocket ship.**

This thought
experiment is a well-known variation of Einstein's light-clock thought
experiment, which has to do with the passage of time.

Let's say you have a twin, born at almost the exact same time as you. But the moment your
twin is born, he or she gets placed in a spaceship and launched into space to
travel through the universe at nearly the speed of light.

According to
Einstein's special theory of relativity, you and your twin would age
differently. Since time moves slower the closer that you get to the speed of
light, your twin would age more slowly.

When the
spaceship lands back on Earth, you might be trying to sort out your retirement,
while your twin is just trying to get through puberty.

**Imagine you're standing in a box.**

Imagine you
are floating in a box, unable to see what's happening outside of the box.
Suddenly, you drop to the floor. So what happened? Is the box being pulled down
by gravity? Or is the box being accelerated by a rope yanking it upward?

The fact
that these two effects would produce the same results led Einstein to the
conclusion that there is no difference between gravity and acceleration - they
are the same thing.

Now consider
Einstein's previous assertion that time and space are not absolute. If motion
can affect time and space, and gravity and acceleration are the same thing,
that means gravity can actually affect time and space.

The ability
of gravity to warp space-time is a huge part of Einstein's general theory of
relativity.

**Imagine you're tossing a two-sided coin.**

Einstein
wasn't the biggest cheerleader for quantum theory. In fact, he was always
coming up with thought experiments to try to disprove it. But it was these
thought experiments that challenged the pioneers of quantum theory to perfect
it down to its finest details.

One of
Einstein's thought experiments had to do with quantum entanglement, which
Einstein liked to call "spooky action at a distance".

Imagine you
have a two-sided coin that can easily be split in half. You flip the coin and,
without looking, hand one side to your friend and keep the other side for
yourself. Then your friend gets on a rocket ship and travels across the
universe.

Then you
look at your coin. You see that in your hand you're holding the heads side of
the coin and instantaneously you know that your friend, who is billions of
light years away from you at this point, is holding the tails side.

If you think
of the sides of these coins as indeterminate, changing back and forth between
heads and tails until the point in time that you look at one, then the coins
can circumvent the speed of light, instantaneously affecting each other
regardless of how many light years separate them.

This article
was originally published by Business Insider.

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