<< Chapter < Page Chapter >> Page >
Δ τ 2 = Δ s 2 = ( Δ t ) 2 .

Therefore Δ τ is the time interval Δ t in the frame of reference where both events occur at the same location. It is the same interval of proper time discussed earlier. It also follows from the relation between Δ s and that Δ τ that because Δ s is Lorentz invariant, the proper time is also Lorentz invariant. All observers in all inertial frames agree on the proper time intervals between the same two events.

Check Your Understanding Show that if a time increment dt elapses for an observer who sees the particle moving with velocity v , it corresponds to a proper time particle increment for the particle of d τ = γ d t .

Start with the definition of the proper time increment:
d τ = ( d s ) 2 / c 2 = d t 2 ( d x 2 + d x 2 + d x 2 ) / c 2 .
where ( dx , dy , dx , cdt ) are measured in the inertial frame of an observer who does not necessarily see that particle at rest. This therefore becomes
d τ = ( d s ) 2 / c 2 = d t 2 [ ( d x ) 2 + ( d y ) 2 + ( d z ) 2 ] / c 2 = d t 1 [ ( d x d t ) 2 + ( d y d t ) 2 + ( d z d t ) 2 ] / c 2 = d t 1 v 2 / c 2 d t = γ d τ .

Got questions? Get instant answers now!

The light cone

We can deal with the difficulty of visualizing and sketching graphs in four dimensions by imagining the three spatial coordinates to be represented collectively by a horizontal axis, and the vertical axis to be the ct- axis. Starting with a particular event in space-time as the origin of the space-time graph shown, the world line of a particle that remains at rest at the initial location of the event at the origin then is the time axis. Any plane through the time axis parallel to the spatial axes contains all the events that are simultaneous with each other and with the intersection of the plane and the time axis, as seen in the rest frame of the event at the origin.

It is useful to picture a light cone on the graph, formed by the world lines of all light beams passing through the origin event A , as shown in [link] . The light cone, according to the postulates of relativity, has sides at an angle of 45 ° if the time axis is measured in units of ct , and, according to the postulates of relativity, the light cone remains the same in all inertial frames. Because the event A is arbitrary, every point in the space-time diagram has a light cone associated with it.

A space time diagram has a space on the horizontal axis and time on the vertical axis. The light cone is a vertical cone above the origin with its vertex at the origin and sides at 45 degrees, and another vertical cone below the origin with its vertex also at the origin. Three events are shown. Event A is at the origin. Event B is inside the light cone. Event C is outside the light cone.
The light cone consists of all the world lines followed by light from the event A at the vertex of the cone.

Consider now the world line of a particle through space-time. Any world line outside of the cone, such as one passing from A through C , would involve speeds greater than c , and would therefore not be possible. Events such as C that lie outside the light cone are said to have a space-like separation from event A . They are characterized by:

Δ s A C 2 = ( x A x B ) 2 + ( x A x B ) 2 + ( x A x B ) 2 ( c Δ t ) 2 > 0 .

An event like B that lies in the upper cone is reachable without exceeding the speed of light in vacuum, and is characterized by

Δ s A B 2 = ( x A x B ) 2 + ( x A x B ) 2 + ( x A x B ) 2 ( c Δ t ) 2 < 0 .

The event is said to have a time-like separation from A . Time-like events that fall into the upper half of the light cone occur at greater values of t than the time of the event A at the vertex and are in the future relative to A . Events that have time-like separation from A and fall in the lower half of the light cone are in the past, and can affect the event at the origin. The region outside the light cone is labeled as neither past nor future, but rather as “elsewhere.”

Questions & Answers

If you lie on a beach looking at the water with your head tipped slightly sideways, your polarized sunglasses do not work very well.Why not?
Rakhi Reply
it has everything to do with the angle the UV sunlight strikes your sunglasses.
Jallal
this is known as optical physics. it describes how visible light, ultraviolet light and infrared light interact when they come into contact with physical matter. usually the photons or light upon interaction result in either reflection refraction diffraction or interference of the light.
Jallal
I hope I'm clear if I'm not please tell me to clarify further or rephrase
Jallal
what is bohrs model for hydrogen atom
Swagatika Reply
hi
Tr
Hello
Youte
Hi
Nwangwu-ike
hi
Siddiquee
hi
Omar
helo
Mcjoi
what is the value of speed of light
Propessor Reply
1.79×10_¹⁹ km per hour
Swagatika
what r dwarf planet
Sivalakshmi Reply
what is energy
Isiguzo Reply
কাজের একক কী
Jasim
কাজের একক কী
Jasim
friction ka direction Kaise pata karte hai
Rahul Reply
friction is always in the opposite of the direction of moving object
Punia
A twin paradox in the special theory of relativity arises due to.....? a) asymmetric of time only b) symmetric of time only c) only time
Varia Reply
b) symmetric of time only
Swagatika
fundamental note of a vibrating string
fasoyin Reply
every matter made up of particles and particles are also subdivided which are themselves subdivided and so on ,and the basic and smallest smallest smallest division is energy which vibrates to become particles and thats why particles have wave nature
Alvin
what are matter waves? Give some examples
mallam Reply
according to de Broglie any matter particles by attaining the higher velocity as compared to light'ill show the wave nature and equation of wave will applicable on it but in practical life people see it is impossible however it is practicaly true and possible while looking at the earth matter at far
Manikant
a centeral part of theory of quantum mechanics example:just like a beam of light or a water wave
Swagatika
Mathematical expression of principle of relativity
Nasir Reply
given that the velocity v of wave depends on the tension f in the spring, it's length 'I' and it's mass 'm'. derive using dimension the equation of the wave
obia Reply
What is the importance of de-broglie's wavelength?
Mukulika Reply
he related wave to matter
Zahid
at subatomic level wave and matter are associated. this refering to mass energy equivalence
Zahid
it is key of quantum
Manikant
how those weight effect a stable motion at equilibrium
Nonso Reply
how do I differentiate this equation- A sinwt with respect to t
Evans Reply
just use the chain rule : let u =wt , the dy/dt = dy/du × du/dt : wA × cos(wt)
Jerry
I see my message got garbled , anyway use the chain rule with u= wt , etc...
Jerry
de broglie wave equation
LoNE Reply
vy beautiful equation
chandrasekhar
Practice Key Terms 4

Get the best University physics vol... course in your pocket!





Source:  OpenStax, University physics volume 3. OpenStax CNX. Nov 04, 2016 Download for free at http://cnx.org/content/col12067/1.4
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'University physics volume 3' conversation and receive update notifications?

Ask