# Limitations of scientific models

Scientific models often have limitations as they are by necessity simpler than the real systems or processes that they are describing, due to us having to be able to understand them.

Scientific models sometimes have to be changed when a discovery is made which contradicts the current model. In this instance, the model either has to be updated so that it agrees with the new experimental data or sometimes the model has to be completely replaced!

A famous example of this is how it was discovered Newton's law of gravitation did not perfectly describe gravity and was actually only an approximation. Newton's law explains how the planets orbit around the sun, but it gives the wrong prediction for the orbit of Mercury. Einstein formulated his general theory of relativity in 1915 to explain this and showed that Newton's law becomes inaccurate when the gravitational forces become very large (like when an object or body is very close to the sun).

Einstein's general theory of relativity predicts many weird and wonderful phenomena that do not come from calculations using Newton's theory.

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Gravitational lensing is caused by massive objects warping space and time.

According to general relativity, objects with mass bend the fabric of spacetime. Extremely massive objects like black holes distort space and time so much in their vicinity that they cause light from background objects to bend and focus around them. This effect is called gravitational lensing and is shown in the image above.

Most scientific models are approximations. They are useful for most situations but they can become inaccurate under certain conditions or when extreme detail is required. A scientific model may also be limited when the system that the model is attempting to describe is impossible to visualise. As we have already discussed, the Bohr model of the atom consists of electrons orbiting around the nucleus in a solar system-type model. However, electrons do not actually *orbit* around the nucleus, the model is inaccurate.

In 1913 Niel's Bohr did not take wave-particle duality into account in his model of the atom. You might already be aware that light can act as both a particle and a wave, but this holds true for electrons too! A more accurate model of the atom would be the **Schrödinger**** model **which takes wave-particle duality into account. You will learn more about this model and its implications if you choose to study physics at A-level.

The main reason Bohr's model is useful is that it clearly demonstrates the underlying structure of the atom and it is relatively neat and accurate. Furthermore, Bohr's model is an important fundamental step at GCSE level to understanding the physics that governs the world.

The most precise idea of an atom that we have today is based on a mathematical description from quantum mechanics, called the Schrödinger model. Instead of the idea of electrons moving in specific and well-defined orbits in the Bohr model, Erwin Schrödinger determined that electrons actually move around the nucleus in different **clouds** according to their energy level. Still, we cannot really tell how they are moving around the atom. We can only know the probability that the electron is at a certain position inside these orbits, according to their energy.

## Scientific Model – Key takeaways

- A scientific model is a physical, conceptual or mathematical representation of a system.
- A good scientific model has predictive power, and explanatory power, and is consistent with other models.
- There are five main types of scientific models:
- Representational models
- Descriptive models
- Spatial models
- Mathematical models
- Computational models

- Physical models consist of physical objects that you can touch.
- Conceptual models use known concepts to help you visualise systems that are maybe impossible to see or understand.
- Mathematical models use known mathematical relationships to make predictions.
- Scientific models often have limitations as they are simpler than the real systems or processes that they are describing.
- A scientific model must be changed or even completely replaced when a new experimental discovery is made which contradicts the model.