What happens if something tries to go faster than light?

In one line

The rule

According to Einstein’s theory of relativity, the speed of light in a vacuum (about 3 lakh km per second) is the maximum speed anything can travel.

The formula for energy needed to move an object is: E = γmc², where γ = 1 / √(1 − v²/c²)

• E: total energy
• m: mass of the object
• c: speed of light (about 3 × 10⁸ m/s)
• v: speed of the object
• γ (gamma): a factor that grows very large as v approaches c

Let's understand it simply

Imagine you are pushing a cycle. At first, it moves easily. As you pedal faster, it gets harder. Now, imagine you try to reach the speed of light — like a Diwali rocket going faster and faster. But as you get closer to that speed, it feels like the cycle gets heavier and heavier. No matter how hard you push, you can never reach or cross the speed of light. It's like running towards a wall that keeps moving away from you.

How it works

1. When an object moves faster, its mass (how heavy it feels) increases due to relativity.
2. As speed (v) gets closer to the speed of light (c), the denominator in γ gets smaller, making γ huge.
3. The energy needed to keep increasing speed grows rapidly.
4. At exactly the speed of light, the energy required becomes infinite (never-ending).
5. Since we can never provide infinite energy, no object with mass can reach or cross the speed of light.

The story behind it

Albert Einstein, a German scientist, came up with this idea in 1905. He was trying to solve problems with how light and motion worked together. Before Einstein, people thought time and space were the same for everyone. Einstein showed that time, space, and speed are connected. His theory changed how we see the universe. One fun fact: Einstein imagined riding on a beam of light as a child, which led him to these questions.

Where you see it in real life

• Particle accelerators (like the Large Hadron Collider): Scientists try to make tiny particles go very fast. They get close to light speed, but never reach or cross it.
• GPS satellites: Their clocks run differently because they move fast and are far from Earth. Engineers must correct for relativity to keep your phone’s map accurate.
• Nuclear reactions: Energy released in bombs or reactors follows Einstein’s famous equation, showing the link between mass and energy.
• Light from stars: No matter how fast a star moves, its light always travels at the same speed.
• Communication with Mars: Signals from Earth to Mars take time, because nothing can go faster than light.
• Science fiction: Stories about spaceships going faster than light break this rule — in real science, it’s not possible.

Why it matters

• Sets the speed limit for the universe: All technology and science must follow this rule.
• Protects cause and effect: If you could go faster than light, you could break the order of events (like seeing the result before the action).
• Used in modern tech: GPS, particle physics, and even your mobile phone’s timing depend on relativity.
• Foundation for advanced physics: Many later chapters (like nuclear physics, cosmology) build on this idea.

Worked example

Let’s see what happens if you try to push a 1 kg object to 99.99% the speed of light.

Given: m = 1 kg, v = 0.9999c, c = 3 × 10⁸ m/s
Step 1: Find γ
      γ = 1 / √(1 − v²/c²)
Step 2: Calculate v²/c²
      v²/c² = (0.9999)² = 0.9998
Step 3: Calculate denominator
      1 − 0.9998 = 0.0002
      √0.0002 ≈ 0.0141
Step 4: γ = 1 / 0.0141 ≈ 71
Step 5: E = γmc² = 71 × 1 × (3 × 10⁸)²
      = 71 × 9 × 10¹⁶
      = 6.39 × 10¹⁸ joules
Step 6: This is huge — more than all the energy India uses in a year!

Common mistakes

• Thinking you just need a bigger engine: No matter how powerful, you can’t reach light speed with mass.
• Believing light speed is only a suggestion: It’s a strict law, not just a guideline.
• Forgetting about massless particles: Only things with zero mass (like photons, which are light particles) can go at light speed.
• Assuming time and space are the same for everyone: At high speeds, time slows down and distances shrink for the moving object.

Remember it

Nothing with mass can go faster than light — it would need endless energy.