# What is the difference between our time and space time?

I am trying to understand the phenomenon of space-time. But, everything on internet seems to be too complicated for me since I do not have a background in physics. Can anyone give me simple explanations for the following:

1. What is the difference between time and space-time?
2. How does gravity affect the passage of time?
3. What is the speed of light and how does it relate to time?
4. How do scientists deal with timescales on the order of billions of years if time is not constant for all observers in the universe?
5. How is time, or for example the age of the universe, actually measured experimentally?
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if I misinterpreted any of your questions after edits, please feel free to re-edit. Many of these are really good questions, and are deserve to be questions by themselves! –  astromax Jan 15 '14 at 3:45
Yup you have correctly interpreted and thanks for the edits :-) –  Asadullah Ali Jan 15 '14 at 6:23
"Space-time" is not a kind of time; it's both space and time, treated as one thing. We live 3 dimensions of space and 1 dimension of time, making the 4 dimensions of space-time. (More recent models suggest 11 dimensions, but the extra 7 exist only on a very small scale.) –  Keith Thompson Jan 15 '14 at 16:51

What is the difference between time and space-time?

Space-time is time plus space.

How does gravity affect the passage of time?

The higher the gravity of a planet or star and the closer to that body the slower the time.

What is the speed of light and how does it relate to time?

The speed of light is 299,792.4580 km/s in vacuum, the speed at which light propagates, roughly 1.3 seconds from Earth to Moon. Velocity is distance divided by time; this applies also to the speed of light.

How do scientists deal with timescales on the order of billions of years if time is not constant for all observers in the universe?

They treat time dependent of the observer. For different observers on Earth variations are tiny, in many cases neglectable in comparison to measurement errors, although not for precision measurements.

How is time, or for example the age of the universe, actually measured experimentally?

There are many ways to measure or estimate ages. The age of the earth can be estimated by ratios of certain radionuclides in the oldest rocks. Estimates of the age of the universe are obtained by simulations based on observations (redshift and distance) of distant galaxies, and on observations of the cosmic microwave background. The redshift is used for a velocity estimate; together with a distance estimate (obtained by stars of known brightness) one can calculate back, when all objects of the universe should have been close together.

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Space, as we experience it, is simply three-dimensional Euklidean (flat) space. A flat space is one in which parallel lines never intersect. Consider the two-dimensional space of your kitchen table: (if your table is new) this space is flat. But the surface of a sphere, also a two-dimensional space, is not flat. In the same way a three-dimensional space can be curved (though this is hard/impossible to imagine).

Time as we experience it is simply linearly progressing. You can combine space and time to a four-dimensional space-time, one dimension of which is time-like. The theory of relativity now says that this four-dimensional space-time is not always exactly flat and that any curvature of space-time is equivalent to a force. Any form of energy (and rest-mass energy is the most compact such form) curves space-time and hence exerts a force -- known as gravity.

This curving of space time affects both space and time, hence gravity also affects clocks etc. For weak forces (any we experience as humans), the curvature effects are extremely minute.

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How is it impossible to imagine? Isn't it it just a 3d space that can change over 4th dimension (time)? –  Ska Dec 28 '14 at 0:06

Particle like, molecule or atoms or any smallest particle behaves differently in different environment. For example, these particle behaves different on earth or on moon or on earth's orbit or near to black hole horizon.
This was actually proved by the theory of relativity given by Albert Einstein. We (Human) have to adjust artificial satellite's clock everyday 0.0000000001 second. Otherwise we will get wrong data from satellite on earth computers and all.
Now IMO, Any object in Gravitational environment or the object travelling at a speed of light must be getting some effect at atomic level and all electromagnetic level also. Because of that clock become slow ( because electromagnetic/atomic movement which requires to produce output in clock becomes slow ).
In the same way, IMO (not validated ), when we travel at the speed of light or roaming near to the black-holes horizon then our biological activity or any electromagnetism which is required to THINK becomes slow in such a way that difference produced by this effect is dramatically big. It is said that, a person on earth become old but the person travelling at a speed of light will think 'I traveled only for a week!'(see, this person's biological/atomic activity become slow, even about thinking) but actually from earth's person's point of view he/she (traveller) traveled for at least 75 year at a speed of light which is real fact. Normally after 75 years anybody will become old on earth. This is all IMO.

What is the speed of light and how does it relate to time?


speed of light is 300000 Km/sec.

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What is the difference between time and space-time?

time: is a change of position and/or energy of matter.

space-time: is a configuration between change of energy and/or position storage into a space , ie. an atom from (Fe) Iron vs foton, gallaxy andromeda vs via lactea, black hole vs star.

How does gravity affect the passage of time?

a set from space-time ( as black hole or star) can change other sets space- time, in this change acelerate position and energy (time).

What is the speed of light and how does it relate to time?

the speed of light is a specific set space-time (configuration) that have a position/energy with a limit into space.

How do scientists deal with timescales on the order of billions of years if time is not constant for all observers in the universe?

it is a ilussion because a speed light or energy emmision as gamma radiation or infrared (space-time sets) has different configurations and interactions, it is only a reference.

How is time, or for example the age of the universe, actually measured experimentally?

they shall create a relation parent set space-time between children sets space-time (Im not sure if they do it).

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