How do scientists know how big and how old the universe is? How on earth have they measured it?

Question

I've kind of got my head around the whole light-year thing but how can scientists say that a planet is sixty million light years away if they haven't had sixty million light years of experiments on it? And how can you measure how old the universe is?
Both I and Mr. GorgeousFluffpot are baffled by this (particularly as his counting isn't very good, anyway).

Answer 1

By evaluating the light spectrum of an object, you can tell if the object is moving closer, or further away by what is called "redshift." You don't need sixty million years to experiment on it, because you can evaluate the light that has been traveling for 60 million years to get to you. You can also tell the velocity at which it is moving by how much of a shift there is. Redshift works just like doppler radar. When a object is moving away from you, there is a shift towards the red spectrum of light because there is an increase in wavelength. If an object moves towards you, there is is a decrease, towards the blue side of the spectrum.

The age of the universe on the other hand, largely depends on if our current understading of the universe is correct, but there are a few ways we try to calculate it using Hubbles constant, which is the ratio of rise of run (the slope) of velocity over distance. (The further away something is, the faster it moves due to the expansion of the universe) By knowing the rate at which the universe expands, you can calculate the "position" of expansion, anywhere the time scale, and make predictions about what will happen in the future.

Answer 2

The Earth is approx. 4.3 Billion years old, the Universe 14 to 16, give or take a few. Without going into the science of it (as others have posted about it), the relative age of the Earth and the Universe are determined by "best guess" using techniques derived from logic and the process known as the scientific method. Assumptions are the variables, and no known factual information can or ever will be given as to pinpoint an exact answer. While the result not entirely accurate, it sure beats the hell out of someone holding a Bible and condemning people for not rigorously following *their* ideals and beliefs.

Answer 3

The aged of the earth is based on the decay of long half life radioactive isotopes, normally of uranium. This gives an age of 4.5 Billion years.

Several others have made posts about measuring Hubble's constant, but this isn' t the only way. There are a number of other limits.

We haven't seen any burnt out white dwarfs - which should occur if the universe was just a bit older than we think it is.

The ratio of Helium 4 to Hydrogen was fixed at the big bang - The modified my the conversion of Hydrogen into helium in stars. We know (sort of) the rate at which hydrogen is being burned so this gives and indication to the age of the universe.

There are others. Basically, yes Hubble's constant is the big one but it is backed up by other observations.

Answer 4

There are a number of tools used to measure distances in the universe. The most obvious is parallax shift: if you take a picture of stars at one time, and another six months later when the earth is on the other side of the sun, the nearer stars will appear to have shifted slightly in position. A shift of one second of arc implies a distance of something like 6.5 light years -- about 38 trillion miles.

The next important tool is a special kind of star called a Cepheid variable. These stars vary their brightness on a regular basis, in a manner which depends on their overall brightness. By measuring the period and apparent brightness of one of these, its distance can be determined. Cepheid variables are widespread, and can be observed in distant galaxies.

Another important tool is the red shift. Distant objects are traveling away from us, at a speed that is proportional to the distance. The speed is determined by observing the Doppler shift of the spectral lines of the object.

If you have a speed that is proportional to a distance, a division gives you a time: specifically, a time at which the distance was zero. That time was 13.6 billion years ago, hence the age of the universe. Boom!

Postscript: The universe is unbounded, but is of finite size. This is a bit hard to grasp (as evidenced by other responses to this question), but is nevertheless true. A popular analogy is to compare the universe to the surface of an expanding balloon: it is of finite size, has no boundaries, and is expanding.

Answer 5

The age of the universe comes from knowing the speed at which the universe is expanding. Scientists believe that the speed of expansion has been pretty constant over the age of the universe so all they do is wind back that expansion on paper until the universe is the size of an atom and that is the time when the big bang occurred. The time from then until now is the age of the universe.

Answer 6

The heat echos of the Big Bang. The universe is about 13.7 billion years old.

Answer 7

A B&Q Tape Measure

Answer 8

the universe is loaded with black
holes-we can only 'see'so far-what
happens beyond that-i don't think that it
is infinite,but it is very large

Answer 9

They can't: it's cobblers.

The universe is everything; logic tells us that there can be nothing outside it. Therefore it cannot have any boundaries, so it is of infinite size.

Either the scientists don't really mean "universe" in the true sense of the word, or they are inventing an answer because they dislike questions without answers.

Generally I respect scientists, so I suspect the former.

Answer 10

Age is measured by carbon dating. Same way they tell how old a dinosaur is.