Tag: Yi Wang

Cosmology is the science of studying our universe. Being different from astronomy, which corresponds to studying some particular objects in our universe, for example, the black holes, neutron stars, etc. Cosmology is to study the universe as a whole object and study the universe itself: An interesting observation is at night the sky is dark,…

Previously, in special relativity, we have found that the concepts of space and time are relative. When you are moving, you will find space and time are different compared to others. However, when you are not moving, gravity will also bring us new understanding about space and time. The Earth gravity is so weak that…

In 3-dimensional space, when we are looking at an object, what we see depends on the angle, the object is still the same object. Actually, the geometry of special relativity is nothing more than looking at a four-dimensional space-time object at different angles. We are actually looking at the relation of events at different angles,…

Lorentz transformation is the central question in the mathematical structure of special relativity. Simply put, given the coordinate of the event in one frame, say Bob’s frame, (tB,xB), calculate the coordinate in another frame, say Alice’s frame (tA,xA). Let us first examine a similar problem, which is the rotation of the space directions. In the…

The concept of “length” and “the same time” have to be reconsidered in special relativity. Light Ruler and Length Contraction In the example of the explosion of a grenade, it takes time ∆t from triggering to exploding. If it is triggered and immediately thrown with speed v, how long the grenade travels depends on your…

For hundreds years, space and time were absolute in the concept of Newton, they are something that can not be changed. Since a hundred years ago, we understood special relativity, space and time were put together – one object that can transform to each other. Further, we have general relativity that space and time are not…