Albert Einstein used to ponder these 5 mind-melting questions for fun. Can you figure them out?

• Albert Einstein was well known for his thought experiments involving complex scientific ideas.
• Often he used real-world examples that helped non-scientists grasp his theories of relativity.
• He started pondering one of them, about chasing a beam of light through space, when he was 16.

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 Gedankenexperiments, which is German for thought experiments.

Despite the name, Einstein's mental exercises incorporated data from actual experiments.

Here are a few thought experiments that demonstrate some of Einstein's most groundbreaking discoveries, including his special and general theories of relativity.

What would happen if you chased a beam of light as it moved through space?

Einstein started wondering about this when he was just 16 years old. 

If you could somehow catch up to the light and travel as fast as it is going, Einstein reasoned, you would be able to observe the light frozen in space. But since he knew light was a wave composed of changing magnetic and electric fields, it couldn't truly be still.   

"One sees in this paradox the germ of the special relativity theory is already contained," Einstein wrote in his "Autobiographical Notes." This "special" theory applies to certain relationships between space and time, and he further explored it with another thought experiment involving trains and light.

Can 2 people experience the exact same event differently? 

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

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

The setup for this experiment is a bit complicated and involves angled mirrors and poles. But the result is that time behaves differently for someone moving than for someone standing still. 

It cemented Einstein's belief that time and space are relative and simultaneity — two events happening at the same time — depends on your perspective. This is a cornerstone of Einstein's special theory of relativity.

How does your space-traveling twin age compared to you?

Let's say you have a twin who was born at almost the exact same time as you.

But almost immediately, your twin boards a spaceship and launches into space to travel through the universe at nearly the speed of light. 

Since, according to Einstein's special theory of relativity, time moves slower the closer you reach the speed of light, your twin in the spaceship would age more slowly.

When the spaceship landed back on Earth, you would be celebrating your 65th birthday, while your twin hadn't even turned 10 yet, based on an estimation from Omni Calculator.

Is your elevator accelerating or floating in space?

Imagine you are in a windowless elevator, unable to see what's happening outside. Without visual cues, you don't know if you're in a stationary elevator on Earth or in space being hauled upwards. Gravity's tug and upward acceleration in zero gravity both pull you to the floor.  

The physics of both events is the same, Einstein decided, based on the "principle of equivalence." Similarly, if your elevator were to plummet far and fast, you would float as though you were in space.

Now consider Einstein's previous assertion that time and space are relative. If motion can affect time and space (like with the train experiment) and gravity and acceleration behave the same, that means gravity can actually affect time and space. 

If you put a bowling ball on a trampoline, it will depress the fabric. Place marbles close by, and they will roll toward the ball. Objects with huge mass can affect space-time in a similar way. 

The ability of gravity to warp space-time is a key part of Einstein's general theory of relativity, which he published a decade after the special theory and expanded upon it.

Can particles communicate faster than the speed of light?

Einstein wasn't the biggest cheerleader for quantum theory. In fact, he argued back and forth with physicist Niels Bohr over certain occurrences that he believed violated fundamental laws of physics.

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

Imagine you have a two-sided coin that you can easily split in half. You flip the coin. Without looking at the outcome, you 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.

When you look at your coin, you see you're holding the heads side of the coin. Instantly you know that your friend, who is billions of light years away, has the tails side.

Einstein's version of this thought experiment is more complicated than coins and involves entangled particles that share a wave function. Both particles have the potential to be in two possible states, spin up and spin down. Measuring one gives you information about the other, no matter how far apart they are.

It's a bit like if your half of the coin was neither heads nor tails until you looked at it. Since the coin wasn't double-sided, you know your friend has tails when you have heads. But Einstein thought particles behaved more like real coins. They had some inherent property that made them "spin up" or "spin down" all along.

Other scientists have proven him wrong in the decades since. In 2022, three physicists won the Nobel Prize for demonstrating spooky action at a distance.