According to hubbles law how old is the universe

They could avoid this collapse only if for some reason they happened to be moving away from each other at high speeds.

In just the same way, only if a rocket is launched at high enough speed can it avoid falling back to Earth. The problem of what happens in an infinite universe is harder to solve, but Einstein and others used his theory of general relativity which we described in Black Holes and Curved Spacetime to show that even infinite universes cannot be static.

Since astronomers at that time did not yet know the universe was expanding and Einstein himself was philosophically unwilling to accept a universe in motion , he changed his equations by introducing an arbitrary new term we might call it a fudge factor called the cosmological constant. This constant represented a hypothetical force of repulsion that could balance gravitational attraction on the largest scales and permit galaxies to remain at fixed distances from one another.

That way, the universe could remain still. Figure 1. Einstein and Hubble: a Albert Einstein is shown in a photograph. Wilson Observatory. About a decade later, Hubble, and his coworkers reported that the universe is expanding, so that no mysterious balancing force is needed. We discussed this in the chapter on Galaxies. Observations are now being carried out to determine whether this acceleration is consistent with a cosmological constant.

In a way, it may turn out that Einstein was right after all. If we had a movie of the expanding universe and ran the film backward , what would we see? The galaxies, instead of moving apart, would move together in our movie—getting closer and closer all the time. Eventually, we would find that all the matter we can see today was once concentrated in an infinitesimally small volume.

Astronomers identify this time with the beginning of the universe. But when did this bang occur? We can make a reasonable estimate of the time since the universal expansion began. Unfortunately, everyone is celebrating with so much enthusiasm that the neighbors call the police, who arrive and send everyone away at the same moment.

You get home at 2 a. But you use a map to measure that the distance between the party and your house is 40 kilometers. No humans were around to look at their watches when the universe began, but we can use the same technique to estimate when the galaxies began moving away from each other. Remember that, in reality, it is space that is expanding, not the galaxies that are moving through static space.

In this case, the time it has taken a galaxy to move a distance, d , away from the Milky Way remember that at the beginning the galaxies were all together in a very tiny volume is as in our example.

If we can measure the speed with which galaxies are moving away, and also the distances between them, we can establish how long ago the expansion began. Making such measurements should sound very familiar.

This is just what Hubble and many astronomers after him needed to do in order to establish the Hubble law and the Hubble constant. We see, then, that the work of calculating this time was already done for us when astronomers measured the Hubble constant. This age estimate is sometimes called the Hubble time. To make numbers easier to remember, we have done some rounding here. To put these uncertainties in perspective, however, you should know that 50 years ago, the uncertainty was a factor of 2.

Remarkable progress toward pinning down the Hubble constant has been made in the last couple of decades. The Hubble time is the right age for the universe only if the expansion rate has been constant throughout the time since the expansion of the universe began.

Continuing with our end-of-the-semester-party analogy, this is equivalent to assuming that you traveled home from the party at a constant rate, when in fact this may not have been the case. In this case, given that you were driving faster at the beginning, the trip home would have taken less than a half-hour. In the same way, in calculating the Hubble time, we have assumed that H has been constant throughout all of time.

It turns out that this is not a good assumption. Earlier in their thinking about this, astronomers expected that the rate of expansion should be slowing down.

We know that matter creates gravity, whereby all objects pull on all other objects. The mutual attraction between galaxies was expected to slow the expansion as time passed.

This means that, if gravity were the only force acting a big if , as we shall see in the next section , then the rate of expansion must have been faster in the past than it is today.

In this case, we would say the universe has been decelerating since the beginning. How much it has decelerated depends on the importance of gravity in slowing the expansion.

If the universe were nearly empty, the role of gravity would be minor. Then the deceleration would be close to zero, and the universe would have been expanding at a constant rate. But in a universe with any significant density of matter, the pull of gravity means that the rate of expansion should be slower now than it used to be. If we use the current rate of expansion to estimate how long it took the galaxies to reach their current separations, we will overestimate the age of the universe—just as we may have overestimated the time it took for you to get home from the party.

Astronomers spent several decades looking for evidence that the expansion was decelerating, but they were not successful. What they needed were 1 larger telescopes so that they could measure the redshifts of more distant galaxies and 2 a very luminous standard bulb or standard candle , that is, some astronomical object with known luminosity that produces an enormous amount of energy and can be observed at distances of a billion light-years or more.

Recall that we discussed standard bulbs in the chapter on Galaxies. If we compare how luminous a standard bulb is supposed to be and how dim it actually looks in our telescopes, the difference allows us to calculate its distance. According to Hubble's constant how old is the universe? May 4, Explanation: It is a scientific surmise that, yet to be identified precisely as what matter it is, Dark Matter prevalent within and in-between galaxies is surmised as responsible for the expansion of our universe.

Related questions Why does intergalactic space expand, but not not galaxies and solar systems themselves? How fast in parsecs is the universe expanding? What is Hubble's Law? The faster the universe is expanding, the faster the galaxies will appear to be moving away from each other. You can actually calculate an estimate for the age of the Universe from Hubble's Law. The distance between two galaxies is D. The apparent velocity with which they are separating from each other is v.

At some point, the galaxies were touching, and we can consider that time the moment of the Big Bang. If you take the separation between the two galaxies D and divide that by the apparent velocity v , that will leave you with how long it took for the galaxies to reach their current separation. The standard analogy here is to consider that you are now miles from home. You drove 60 mph the entire time, so how long did it take you to get here?