**Time Dilation**

**What is Time Dilation ?**

**Types of time dilation**

Relative Velocity Time Dilation

Gravitational Time Dilation

Example of Relative velocity time dilation

**by John Andrews**

Based upon Albert Einstein's theory of relativity

gravitational forces distort spacetime

large masses produce gravity forces

Time dilation is an actual difference of elapsed time between two events as measured by observers either moving relative to each other or differently situated from gravitational masses.

Speed of light is constant for all observers

Real World Example of Time Dilations

accelerations produce g-forces

a

b

c

STATIONARY SPACE STATION

(reference point)

unaffected by any time dilations

not to scale!

TRAVELING SPACESHIP

(velocity =.866*c = 86.6% speed of light)

upon which near speed of light velocity slows time

a

b

c

not to scale!

time elapsed on space station = t_station

if After 10 years of time upon the space station, person a decided to meet up with B and C

Aged 10 years

Aged only 8 years

Aged only 5 years

EXTREMELY DENSE NEUTRON STAR

where gravity slows time

time elapsed on neutron star = 0.8*t_station

time elapsed on board spaceship = 0.5*t_station

STATIONARY SPACE STATION

(reference point)

unaffected by any time dilations

TRAVELING SPACESHIP

(velocity =.866*c = 86.6% speed of light)

upon which near speed of light velocity slows time

EXTREMELY DENSE NEUTRON STAR

where gravity slows time

4350 mph

17,000 MPH

**another example**

consider 2 spaceships

stationary spaceship

spaceship moving at 50% speed of light

stationary spaceship

at time t = 0, both fire a laser

spaceship moving at 50% speed of light

stationary spaceship

spaceship moving at 50% speed of light

stationary spaceship

spaceship moving at 50% speed of light

Time dilation and Lorentz Factor

**Questions?**

**Conclusion**

c = 186,000 miles/s

fastest man made object to date (Helios a & B probes) = 43.63 miles/s

time dilation for this object is only 1.0000000275115 * t

which translates to an aging difference of .856 seconds/year

velocity << C => time dilation negligible

velocity < c => time is slowed for the traveler

velocity = c => the traveler has displacement over zero time

Velocity > C => Time flows in the reverse direction

the next closest star, Proxima Centauri, is over 4.2 light-years away. THat's 2.464*10^13 miles away. That would take helios A around 17,900 years to reach...