Quantum Tunnelling
Quantum Tunnelling and the Myth of Instant Space Travel.
Introduction
🚀 Science Fiction vs. Science Fact.
In many science fiction stories, spaceships use “quantum tunnelling drives” to vanish from one point in the universe and reappear instantly on the other side—no fuel, no time delay, just a quantum leap. Science fiction often portrays quantum tunnelling as a magical shortcut through space and time. It sounds thrilling—but is it scientifically possible?
To answer this, we must understand what quantum tunnelling really is, how it works, and why it cannot (at least with current physics) be scaled up to move a spaceship across space and time.
What Is Quantum Tunnelling?
🧠 Definition
Quantum tunnelling is a quantum mechanical phenomenon where particles like electrons or protons, can pass through a potential energy-barrier, even when they do not have enough kinetic energy to overcome it in the classical sense.
Everyday Analogy
Imagine rolling a ball up a hill. If it lacks the energy to reach the top, it rolls back down. In our macroscopic world, the ball never appears on the other side.
At the quantum scale, however, particles like electrons behave as waves. Their wave function can extend through the barrier, giving a 'non-zero probability' that the particle will be detected on the other side.
So, in terms of quantum mechanics, the ball (particle) would have a very slight chance (non-zero probability) of appearing on the other side of the hill—without climbing it. No one has ever seen a ball do this, though.
The Principle Behind Tunnelling
The effect comes from the wave-particle duality of matter, a cornerstone of quantum mechanics.
Based on wave-particle duality:
- Physical particles can also behave like waves.
- The wave function describes the probability of a particle’s location.
Key Steps in Quantum Tunnelling:
1. A particle’s wave function approaches a barrier.
2. Inside the barrier, the wave function decays exponentially but does not drop to zero.
3. If the barrier is thin enough, part of the wave function continues beyond it.
4. This means there is a finite (though often tiny) chance the particle will appear on the other side.
📊 Quantum Tunnelling Process
| Classical Physics | Quantum Mechanics |
| Particle blocked by barrier. | Particle has a chance to tunnel through. |
| Requires enough energy. | Can tunnel with insufficient energy. |
| Predictable outcome. | Probabilistic outcome. |
Table A: Behaviour of a particle in classical physics as compared to quantum mechanics.
📊 Barrier Thickness vs. Tunnelling Probability
| Barrier Thickness (nm) | Probability of Electron Tunnelling |
| 0.5 | High. |
| 1.0 | Moderate. |
| 3.0 | Alomost zero. |
Table B: Probability of Quantum Tunnelling by a particle with regard to thickness of the barrier encountered.
Real-World Examples
Quantum tunnelling is not science fiction—it is measurable and used in technology and nature.
| Application | How Tunnelling Works | Impact |
| Scanning Tunnelling Microscope (STM) (Binnig & Rohrer, 1981). | Electrons tunnel between a sharp tip and a surface, creating atomic-scale images. | Revolutionised nanotechnology. |
| Nuclear Fusion in the Sun | Hydrogen nuclei tunnel through their mutual electrostatic repulsion (Coulomb barrier). | Powers the Sun’s energy output. |
| Flash Memory | Electrons tunnel through a thin insulator to store binary data. | Enables USB drives and SSDs. |
Table C: Real world examples of quantum tunnelling in technology and nature.
Why Spaceships Cannot Tunnel Through the Universe
Science Fiction Claim:
A spaceship could “tunnel” through space-time, bypassing the speed of light.
Scientific Reality:
- Scale Problem: Tunnelling probabilities drop exponentially with barrier width and particle mass. A spaceship is made of ~10²⁷ particles. Coordinating them to tunnel together is astronomically improbable.
- Energy and Environment: In the Sun, tunnelling works because trillions of particles try every second under extreme temperatures and pressures. Space travel offers no such conditions.
- Relativity Constraint: Even if tunnelling appears instantaneous for a particle, Einstein's relativity forbids faster-than-light transfer of usable information or matter.
Cause-and-Effect Reasoning
Cause: Particles have wave-like properties.
Effect: They can sometimes appear beyond an energy barrier without crossing it in the classical sense.
Limitation: The effect is significant only for very small particles over very short distances.
Conclusion: Scaling this to macroscopic objects like spaceships is beyond known physics.
Timeline of Key Discoveries
| Year | Scientist(s) | Contribution |
| 1927 | Friedrich Hund | First theoretical description of tunnelling in molecules. |
| 1928 | George Gamow; Gurney & Condon | Applied tunnelling to explain alpha decay in nuclei |
| 1958 | Leo Esaki | Discovered electron tunnelling in semiconductors (tunnel diode). |
| 1981 | Gerd Binnig & Heinrich Rohrer | Invented the STM using tunnelling currents. |
Table D: Timeline of discoveries with regard to tunnelling effect.
Respecting Nature’s Limits
Understanding quantum tunnelling teaches us that nature has boundaries. While it inspires futuristic ideas, it also reminds us to respect the laws of physics and focus on achievable, sustainable technologies—like improving propulsion efficiency or harnessing fusion power for space travel.
Summary
- Quantum tunnelling is real, but it works for subatomic particles over nanometre distances.
- It powers technologies like STM, flash memory, and fuels the Sun’s fusion.
- Spaceship-scale tunnelling is not possible with current science due to probability, energy, and relativistic limits.
- Science fiction can inspire, but science keeps us grounded in reality.
💡Challenge Question
If quantum tunnelling cannot move a spaceship, could it still play a role in future space technology—perhaps in energy generation or sensors? Think about how small-scale effects might support large-scale missions.
🌟Well Done!
Well done for exploring one of quantum physics’ most fascinating phenomena! Your curiosity is the best fuel for discovery.
📚 References
- Binnig, G., & Rohrer, H. (1982). Scanning tunnelling microscopy. Helvetica Physica Acta, 55, 726–735.
- Gamow, G. (1928). Quantum theory of the atomic nucleus. Proceedings of the Cambridge Philosophical Society, 24, 89–100.
- Griffiths, D. J., & Schroeter, D. F. (2018). Introduction to Quantum Mechanics (3rd ed.). Cambridge University Press.
- Quantum tunnelling – Wikipedia: https://en.wikipedia.org/wiki/Quantum_tunnelling.
- Exploring Quantum Tunnelling: Applications and Implications – Quantum Zeitgeist: https://quantumzeitgeist.com/exploring-quantum-tunneling-applications-and-implications/.