🔹 Newton’s 3rd law in simple words:

When one thing pushes another, the second thing pushes back with the same force in the opposite direction. This is really about momentum moving between objects.

🔹 How does this connect to light?

• Light is not just brightness. It is a flow of photons, which are tiny packets of energy.

• Even though photons have no rest mass, they still carry momentum.

• Momentum is like the "push power" of moving things.

• If light has momentum, it can push on objects.

  
  

🔹 What happens when light hits something?

Imagine sunlight hitting a shiny mirror in space:

1. The photons in the sunlight arrive at the mirror with momentum.

2. When they bounce off, they change direction.

3. Changing direction means their momentum changes.

4. Momentum cannot just disappear, so the mirror takes the opposite momentum.

   
   

This makes the mirror get a tiny push. At the same time, the mirror “pushes back” on the photons to change their path.That equal and opposite push is exactly Newton’s 3rd law happening with light.

🔹 What if light is emitted?

When an atom or a laser emits light:

1. Photons shoot out in one direction.

   
   

2. To balance the momentum, the atom or laser gets a tiny recoil in the opposite direction.

Even though this recoil is extremely small, scientists can measure it in experiments.

🔹 Real-world proofs:

• Solar sails: Spacecraft use huge shiny sails to catch sunlight. The tiny push from light builds up and moves the craft.

  
  

• Laser recoil: When a high-power laser fires, it feels a small backward thrust.

  
  

• Atomic physics: When atoms emit photons, the recoil changes their energy slightly, something we see in quantum experiments.

  
  

🔹 Why this happens :

Newton’s 3rd law is really just a simple form of a bigger rule:Total momentum in the universe is always conserved.

Light, even without mass, carries momentum because energy and momentum are linked. Whenever photons hit or leave something, they trade momentum with it. This trade creates the equal and opposite forces we call Newton’s 3rd law.

✅ So yes: Newton’s 3rd law absolutely works for light.Light may not have mass, but it has momentum, and that momentum makes action and reaction real whenever light meets matter.