### Relativity and the Quantum / Elementary Tour: Conclusion

The combination of relativity and quantum theory has led to some of the greatest triumphs of theoretical physics, but also to its most persistent unsolved questions. The marriage of special relativity and quantum concepts leads to so-called relativistic ...

### Relativity and the Quantum / Elementary Tour part 5: Superstrings and universal harmony

If you go by the number of researchers involved in it, string theory is the most actively studied candidate for a theory of quantum gravity. String theory is descended from the ordinary models of particle physics, but with a crucial difference: Its basic ...

### Relativity and the Quantum / Elementary Tour part 4: Loop quantum gravity

From the point of view of Einstein´s theory, it comes as no surprise that all attempts to treat gravity simply like one more quantum force (on par with electromagnetism and the nuclear forces) have failed. According to Einstein, gravity is not a force – it ...

### Relativity and the Quantum / Elementary Tour part 3: The need for quantum gravity

So far in the pages of Elementary Einstein, we have encountered two examples in which the limits of general relativity were reached. Both cases involved space-time-singularities. The first example lurked in the interior of a black hole. As briefly described ...

### Relativity and the Quantum / Elementary Tour part 2: Evaporating black holes?

Can the concepts of relativistic quantum field theory be carried over to curved spacetimes, which include gravitational sources and are described by general relativity? The answer is a cautious "yes". The most notable step in this direction was taken by the ...

### Cosmology / Elementary Tour: Conclusion

In the context of Einstein's general theory of relativity, one can formulate cosmological models, called big bang models. They give a reliable picture for the past 14 billion years of the evolution of our universe, which can be tested by comparing predictions ...

### Cosmology / Elementary Tour part 5: Dark matter and dark energy

While the predictive power of the big bang models is impressive, they also show us what we don't know about the universe. Not only about the distant past, as detailed on the previous page, but also about the present universe: If you look around, all material ...

### Cosmology / Elementary Tour part 3: The early universe

An expanding universe, with the distances between galaxy increasing all the time, must have been much more dense, and the galaxies much closer together, in the past. The details follow from Einstein's equations which connect the way expansions runs its course ...