The expanding universe points to a beginning of the universe in the finite past, just as does Genesis 1.Note that this does not make you special! Each raisin would see all other raisins receding from it.
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How do you measure star speeds?The sound from speeding car or train whistle drops in pitch and increases in wavelength as it passes you, a phenomenon known as the Doppler effect. Similarly, light from a star or galaxy that is receding from us is shifted toward long wavelengths (red shift) by an amount that is proportional to its recession speed. Since each atom has a unique spectral fingerprint, we know what the wavelength is in its rest frame, so can measure the amount of shift and therefore the speed. Speeds in excess of 90% of the speed of light have been measured.
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How do you know space is expanding?Because we can measure the distance to stars, it has been discovered that the speed of recession of distant stars and galaxies is proportional to their distance, a fact known as the Hubble law. Since Hubble's experiments of the 1920's, it has been clear that more distant celestial objects in all directions from the solar system are moving faster. This is unambiguous evidence of an expanding universe.
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How do you know measure the distance to stars?The distance to nearby stars can be measured by observing how much their position shifts relative to very distant stars at times six months apart. This process is called parallax distance measurement. If the position of a star shifts one arcsecond, the distance is said to be one parsec. From measurements of many such objects, we have discovered various types of objects like Cepheid variable stars and Type 1a supernovae which can be used as "standard candle" objects where their distance can be calculated from their relative brightness. A combination of overlapping techniques form a distance ladder for measuring astronomical distances.
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How do you know measure time?Since the velocity of light is finite, observations of stars and galaxies are always observations of how they were at some time in the past. Astronomy and cosmology are fields that study past phenomena, and the relevant time is the "lookback time". The nearest star is 4 lightyears away, so we are seeing it as it was 4 years ago. To the extent that we can measure the distance to astronomical objects, we can imply the lookback time to the objects since we are confident that the speed of light is constant.
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How do you know the speed of light is constant?
From laser reflection times and radar echo times off the moon and other bodies, we know the speed of light with great precision. Also, the speed of light is one of the fundamental physical constants of nature and as such is embedded in many other physical phenomena that we can measure precisely. From the force between electric charges to the spectral fingerprints of atoms and the radioactive decay rates of isotopes, everything we see points to the speed of light as one of the fixed parameters in the fabric of the universe.
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