How Do Scientists Know the Universe is Expand

[Picturesque Orion]

How Do Scientists Know the Universe is Expanding?

We thought we’d ask Geza Gyuk, Director of Astronomy at the Adler Planetarium and a research scientist at the University of Chicago. Here's what he said:

A few years after Albert Einstein had developed his famous (and by now very well tested!) theory of General Relativity (GR) in 1915 he applied it to the entire universe and found something remarkable. The theory predicts that the whole universe is either expanding or contracting. There really isn't any other alternative. To have the universe staying static is like a pencil balanced on its point... possible, but very, very unlikely and not liable to last for very long.

In 1929 the astronomer Edwin Hubble measured the velocities of a large selection of galaxies. He expected that about equal numbers would be moving toward and away from us. After all, the Earth isn't a particularly special place in the universe.

Instead, he discovered that almost all galaxies are moving away from us!

Since the time of Hubble we have observed millions of galaxies with better equipment and verified his results. With the exception of a small handful of galaxies close to us, every galaxy is moving away from us.

And in fact, the farther away a galaxy is the faster it is moving away from us. This fits in very well with Einstein's predictions. The galaxies seem to be receding from us because the entire universe is getting larger. The space in between the galaxies is stretching! And the farther away a galaxy is the more space there is to stretch so the faster the galaxy appears to move away from us.

Over the past half-century astronomers have observed many other facts about the universe that all point to the fact that the universe is expanding. While a very inventive person might be able to explain away one or at most two of these discoveries, the expansion of the universe is the only theory that can explain all of them at once. And with each passing year the evidence piles up higher!

This new Hubble image of the Orion Nebula shows dense pillars of gas and dust that may be the homes of fledgling stars, and hot, young, massive stars that have emerged from their cocoons and are shaping the nebula with powerful ultraviolet light. Credit: NASA, ESA, M. Robberto (Space Telescope Science Institute/ESA) and the Hubble Space Telescope Orion Treasury Project Team.

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[Truffles]

Nice Pic Alex!

[greggK]

When you look at that picture, ask yourself, 'Where did all of that 'space dust' come from?'

Better than that, 'What happens to all of that dust?'

What happens to oil in water?

According to Einstein, it is being sucked into black holes. Our Milky Way galaxy is the same, big arms of dust and planets revolving around a black hole. Are we being sucked into it? I don't think the planets are, but the dust may be to be formed into planets to come out again at the other end of the singularity at the center of the galaxy. This is where the definition of 'white hole' comes in.

Every little blip that you see in the night sky is a singularity.

Instead, he discovered that almost all galaxies are moving away from us!

It might be the galaxies are going nowhere, only shrinking in size.

Edited January 28, 2008 by greggK

[Picturesque Orion]

When you look at that picture, ask yourself, 'Where did all of that 'space dust' come from?'

Better than that, 'What happens to all of that dust?'

What happens to oil in water?

According to Einstein, it is being sucked into black holes. Our Milky Way galaxy is the same, big arms of dust and planets revolving around a black hole. Are we being sucked into it? I don't think the planets are, but the dust may be to be formed into planets to come out again at the other end of the singularity at the center of the galaxy. This is where the definition of 'white hole' comes in.

Every little blip that you see in the night sky is a singularity.

The milky way isn't actually being 'sucked' into a black hole, and the reason the milky way is rotating is becuase of the natural momentum from it's formation.

Everything doesn't actually fall into a black hole, actually most of it orbits the black hole at incredible speeds, only some stellar gas and dust fall, but the majority stays in an orbit. Not quite stable though.

Also there is absolutly NO evidence of the existence of white holes, they are kind of a myth, sci-fi.

It might be the galaxies are going nowhere, only shrinking in size.

It's not only because of size that astronomers determine this but also because of the Doppler effect.

The Doppler effect is the change in frequency and wavelength of a wave as perceived by an observer moving relative to the source of the waves. For waves that propagate in a wave medium, such as sound waves, the velocity of the observer and of the source are relative to the medium in which the waves are transmitted. The total Doppler effect may therefore result from motion of the source or motion of the observer or motion of the medium. Each of these effects is analysed separately. For waves which do not require a medium, such as light or gravity in special relativity, only the relative difference in velocity between the observer and the source needs to be considered.

The Doppler effect for electromagnetic waves such as light, is of great use in astronomy, and results in either a so-called redshift or blueshift. It has been used to measure the speed at which stars and galaxies are approaching or receding from us, that is, the radial velocity. This is used to detect if an apparently single star is, in reality, a close binary and even to measure the rotational speed of stars and galaxies.

The use of the Doppler effect for light in astronomy depends on our knowledge that the spectra of stars are not continuous. They exhibit absorption lines at well defined frequencies that are correlated with the energies required to excite electrons in various elements from one level to another. The Doppler effect is recognizable in the fact that the absorption lines are not always at the frequencies that are obtained from the spectrum of a stationary light source. Since blue light has a higher frequency than red light, the spectral lines of an approaching astronomical light source exhibit a blueshift and those of a receding astronomical light source exhibit a redshift.

Among the nearby stars, the largest radial velocities with respect to the Sun are +308 km/s (BD-15°4041, also known as LHS 52, 81.7 light-years away) and -260 km/s (Woolley 9722, also known as Wolf 1106 and LHS 64, 78.2 light-years away). Positive radial velocity means the star is receding from the Sun, negative that it is approaching.

In short words a star or galaxy approaching our point of view will appear more blueish, and receding star or galaxy will appear more redish.

Redshift of spectral lines in the optical spectrum of a supercluster of distant galaxies (right), as compared to that of the Sun (left).

I could alos explain the Doppler effect with sound but that would make another large post, but basically it happens when for example an anbulance is approaching you will hear the sound at a high pitch, as it passes the the sound pitch will lower, when it is receding you the pitch will be lower. Try it for yourself.

Edited January 28, 2008 by Alex01

[MID]

Nice post Alex...

Very nicely done.

How do scientists know...Doppler Shift.

That's basically it.

Cool stuff!

[greggK]

I could alos explain the Doppler effect with sound but that would make another large post, but basically it happens when for example an anbulance is approaching you will hear the sound at a high pitch, as it passes the the sound pitch will lower, when it is receding you the pitch will be lower. Try it for yourself.

How many humans populate the stellar expanse? If your answer is what I think it is, then how can you take a human concept and use it to explain something millions of light years away from you? Doppler radar is good for predicting rain or snow, but I think it is worthless in planetary science. It makes for interesting pictures, but it's an idol. The only words that it says is what you put into it. 'The pictures mean this, then this says that, bla bla bla.'

Also there is absolutly NO evidence of the existence of white holes, they are kind of a myth, sci-fi.

You're right but the myth started with Albert Einstein and his General Relativity. I guess I could go along with the thought that a black hole and a white hole are the same thing, just opposite ends. If you take as a myth or sci-fi, that's OK. The existence of white holes is like the Mayan prophesy or the expansion of the universe; we just don't know.

Everything doesn't actually fall into a black hole, actually most of it orbits the black hole at incredible speeds, only some stellar gas and dust fall, but the majority stays in an orbit. Not quite stable though.

Yeah, that's what causes the light that you see in the middle of the galaxy because of the incredible speed of the particles when they collide.

And I was wondering now, the scientist who are watching the heavens report on planets being born from places like Sag A*, the middle of our Milky Way galaxy. What do they say about that? Is the middle of the sun a black hole?

[Picturesque Orion]

How many humans populate the stellar expanse? If your answer is what I think it is, then how can you take a human concept and use it to explain something millions of light years away from you? Doppler radar is good for predicting rain or snow, but I think it is worthless in planetary science. It makes for interesting pictures, but it's an idol. The only words that it says is what you put into it. 'The pictures mean this, then this says that, bla bla bla.'

I think you should study general physics or atleast do some research before asking me such questions and considerating scientific fact as worthless.

Yeah, that's what causes the light that you see in the middle of the galaxy because of the incredible speed of the particles when they collide.

Do you realise what a stupid comment you have just made sir? Please inform yourself on this matter before making such claims.

Edited January 29, 2008 by Alex01

[Tiggs]

Question: How do we know that space is expanding, as opposed to all the matter within the Universe shrinking?