Relativity

Understanding Einstein's theories of special and general relativity

Topics

How does gravity bend space-time?

Gravity bends space-time because mass and energy curve the four-dimensional space-time fabric. According to general relativity, objects with mass create curvature, and other objects follow these curved paths, which we experience as gravitational attraction.

How does special relativity differ from general relativity?

Special relativity deals with objects moving at constant speeds in flat (non-curved) spacetime, describing time dilation and length contraction. General relativity extends this to include acceleration and gravity, describing gravity as the curvature of spacetime caused by mass and energy.

What are gravitational waves?

Gravitational waves are ripples in spacetime caused by accelerating masses, predicted by Einstein's general relativity. They travel at light speed, stretching and compressing space as they pass. Massive objects like merging black holes or neutron stars create detectable gravitational waves.

What is a black hole?

A black hole is a region of spacetime where gravity is so strong that nothing, not even light, can escape once it crosses the event horizon. Black holes form when massive stars collapse, creating extreme spacetime curvature described by Einstein's general relativity.

What is E=mc²?

E=mc² is Einstein's famous equation showing that energy (E) and mass (m) are equivalent, with c being the speed of light. It means mass can convert to energy and vice versa, explaining nuclear reactions and the energy in matter.

What is length contraction?

Length contraction (also called Lorentz contraction) is the phenomenon where objects appear shorter in the direction of motion when moving at speeds close to light speed. From a stationary observer's perspective, moving objects contract, with contraction increasing as speed approaches light speed.

What is relativity?

Relativity is Einstein's theory describing how space, time, and gravity work. Special relativity deals with objects moving at constant speeds, showing that time and space are relative. General relativity describes gravity as the curvature of space-time.

What is space-time?

Space-time is the four-dimensional combination of three spatial dimensions (length, width, height) and one time dimension. According to general relativity, mass and energy curve space-time, and this curvature is what we experience as gravity.

What is time dilation?

Time dilation is the effect where time passes slower for objects moving at high speeds relative to an observer. According to special relativity, moving clocks run slower than stationary ones, and this effect becomes significant near light speed.

Why can't anything travel faster than light?

Nothing can travel faster than light because reaching light speed would require infinite energy. As objects approach light speed, their mass increases and time dilates, requiring exponentially more energy. At light speed, these effects become infinite, making it physically impossible for anything with mass to reach or exceed this limit.