To address this question, we should first understand the relationship between temperature and particle motion.
1. Temperature and Particle Motion:
- Temperature is a measure of the average kinetic energy of the particles in a substance. Higher temperatures correspond to greater kinetic energy and therefore more vigorous particle motion.
2. Absolute Zero:
- Absolute zero (0 Kelvin) is the theoretical temperature at which all particle motion ceases. This temperature is equivalent to -273.15 degrees Celsius.
- At absolute zero, it's theorized that particles would have no kinetic energy and therefore no motion. However, reaching absolute zero is an idealization and not practically achievable.
3. Quantum Mechanics:
- According to quantum mechanics, due to the Heisenberg Uncertainty Principle, particles can never have precisely zero energy. This means that even at temperatures approaching absolute zero, particles retain some zero-point energy and exhibit minimal quantum mechanical motion.
4. Cosmic Microwave Background:
- The cosmic microwave background radiation (CMBR) is the afterglow of the Big Bang and permeates the universe. Its temperature is approximately 2.7 Kelvin.
- At 2.7 Kelvin, particles possess some energy and thus exhibit motion, albeit very minimal.
Combining these points:
1. Theoretical Possibility:
- In theory, achieving absolute zero where particles have no motion is not possible due to the constraints imposed by quantum mechanics.
2. Practical and Observable Universe:
- Given the omnipresent CMBR at 2.7 Kelvin, any substance in space is exposed to this radiation, thereby preventing it from reaching temperatures low enough to stop all particle motion entirely.
- Practically speaking, even the coldest regions in space have particles with some motion because they cannot be isolated from the CMBR.
### Conclusion:
It is extremely unlikely that a substance with particles exhibiting no motion exists. Particle motion is fundamentally linked to the temperature of the environment, and with the cosmic microwave background radiation setting a base temperature of approximately 2.7 Kelvin throughout space, substances cannot reach the state of absolute zero where all particle motion ceases. Therefore, particles always possess some degree of motion, consistent with the principles of quantum mechanics and the observed thermal nature of the universe.
