What happens when a needle hits the Earth at the speed of light?

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With classical physics, you would expect nothing to happen.

The mass of an average needle is around 1 gram, or around 0.001 kg.

The mass of our planet is an immense 5.9 x 10^24 kg.

The needle is moving at the speed of light, or around 300,000,000 m/s.

The Earth is moving at a much lower speed, 30,000 m/s.

And if you use conservation of momentum, you will find that there is literally no reaction between the two. Although the needle is moving at such a high speed, the mass of the Earth is so comparatively immense.

However, with relativity, as an object approaches the speed of light, its momentum approaches infinity.

Because of this, it doesn’t matter what the mass or velocity of the object the particle at the speed of light is striking, since it has infinite momentum, the collision will result in a massive loss of kinetic energy.

And such a wave of kinetic energy, combined with the impact of the collision, will probably destroy our planet and all life on it.

So let’s hope that a harmless needle doesn’t suddenly get a grudge against our planet and decide to attack it.