Particle like, molecule or atoms or any smallest particle behaves differently in different environment. For weak forces (any we experience as humans), the curvature effects are extremely minute. This curving of space time affects both space and time, hence gravity also affects clocks etc. 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. 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. You can combine space and time to a four-dimensional space-time, one dimension of which is time-like. Time as we experience it is simply linearly progressing. In the same way a three-dimensional space can be curved (though this is hard/impossible to imagine). But the surface of a sphere, also a two-dimensional space, is not flat. Consider the two-dimensional space of your kitchen table: (if your table is new) this space is flat. A flat space is one in which parallel lines never intersect. Space, as we experience it, is simply three-dimensional Euklidean (flat) space. 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. 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 age of the earth can be estimated by ratios of certain radionuclides in the oldest rocks. There are many ways to measure or estimate ages.
How is time, or for example the age of the universe, actually measured experimentally? For different observers on Earth variations are tiny, in many cases neglectable in comparison to measurement errors, although not for precision measurements. They treat time dependent of the observer. How do scientists deal with timescales on the order of billions of years if time is not constant for all observers in the universe? Velocity is distance divided by time this applies also to the speed of light. 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. What is the speed of light and how does it relate to time? The higher the gravity of a planet or star and the closer to that body the slower the time. How does gravity affect the passage of time? What is the difference between time and space-time?
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