What Does It Mean When We Say Our Universe Is Expanding?

[kronecker]

i don't know much about physics but what do people mean by 'our universe is expanding' ? thoug we see the truth that no thing is getting larger/longer. what is the proof for this expansion ?
thanx

 

[mathman]

What Hubble observed is that most galaxies (exceptions being nearby) were moving away from us and that the speed was approximately proportional to distance from us. Expansion of the universe, meaning increasing space between gaalxies, was the explanation.

 

[Chronos]

Sticky wicket. As mathman pointed out, the short answer is most everything is running away from us [after 4.5 billion years wearing the same crust, the Earth tends to have that effect on other galaxies]. The thorn on the rose, is the universe is dynamic. It must either expand or contract to continue to exist for as long as it evidently has. Einstein was the first [most probably] to realize this. When he started working out the solutions to GR field equations, he reached a startling conclusion. The universe must ultimately collapse under the inexorable force of gravity. He viscerally rejected that premise on logical grounds... if the universe must collapse, there is no good way to explain why it has not already done so [hence rendering the entire question moot]. To do otherwise would confer a priveleged reference frame to our very own existence. Given his entire GR premise was based on background independence, he 'fudged' in a cosmological constant that restored the universe to a static, eternal state he was comfortable with [as well as 'mainstream' scientists back then]. He later abandoned that notion, with relief, when Hubble discovered the universe was expanding [despite the fact Hubble was never entirely satisfied with his apparent discovery]. Modern science has since restored the concept for lack of a better explanation that fit later observations. Cosmology is a fickle mistress. The three blind men who described an elephant using the braille system probably arrived at a better theoretical model than we have to date. That's what makes it fun.

 

[turbo]

nice concise explanation

Sticky wicket. As mathman pointed out, the short answer is most everything is running away from us [after 4.5 billion years wearing the same crust, the Earth tends to have that effect on other galaxies]. The thorn on the rose, is the universe is dynamic. It must either expand or contract to continue to exist for as long as it evidently has. Einstein was the first [most probably] to realize this. When he started working out the solutions to GR field equations, he reached a startling conclusion. The universe must ultimately collapse under the inexorable force of gravity. He viscerally rejected that premise on logical grounds... if the universe must collapse, there is no good way to explain why it has not already done so [hence rendering the entire question moot]. To do otherwise would confer a priveleged reference frame to our very own existence. Given his entire GR premise was based on background independence, he 'fudged' in a cosmological constant that restored the universe to a static, eternal state he was comfortable with [as well as 'mainstream' scientists back then]. He later abandoned that notion, with relief, when Hubble discovered the universe was expanding [despite the fact Hubble was never entirely satisfied with his apparent discovery]. Modern science has since restored the concept for lack of a better explanation that fit later observations. Cosmology is a fickle mistress. The three blind men who described an elephant using the braille system probably arrived at a better theoretical model than we have to date. That's what makes it fun.

Very good explanation at the non-technical level, Chronos. It is important that people new to cosmology understand that the 20th century's (arguably) top mathematical theoretician and top observational astronomer were both ambivalent about some aspects of their own work (or the implications thereof). The air of certainty conferred on the standard model of cosmology should not preclude thoughtful inquiry into alternatives.

 

[Chronos]

Indeed, agreed on all counts, Turbo. Some of the most legendary scientists of the past century or so were their own fiercest critics. This trait is not only admirable and desirable, it enhanced their contributions and facilitated general acceptance of their work. Here is a nice article.
http://www.punsterproductions.com/~sciencehistory/cautious.htm
I think, at least hope, this is the example followed by most modern theorists. They are probably less confident in their models than it sometimes appears. On the other hand, they have a better feel for where the good 'hunting spots' are than do we.

It is certainly true there is more pressure to churn out new results than to drive another stake into the heart of prospects that appear unlikely to pan out. This approach, of course, assumes the risk of wasting time and resources barking up the wrong tree. On the other hand, the research that is done will eventually force them back onto the right path. If there are serious flaws in the model, it should collapse under its own weight at some point - and hopefully sooner than later.

Scientists, on the whole, tend to do a poor job explaining why they pursue one idea and not others. Their peers understand, and that's about all that matters to them. Unfortunately, the people who end up trying to explain it to the rest of us are lesser experts and occasionally give ambiguous, even bad information. This just fuels the fire, somtimes to the point people think they are being deliberately misled. There are also those who take advantage of this to promote their own agendas. Their motivations range from scamming for profit, feeding their own delusions, or simple puffery. These are the spiders that spin the web of deception. You don't have to google much to find them. Skepticism is your friend.

 

[turbo]

Indeed, agreed on all counts, Turbo. Some of the most legendary scientists of the past century or so were their own fiercest critics. This trait is not only admirable and desirable, it enhanced their contributions and facilitated general acceptance of their work. Here is a nice article.
http://www.punsterproductions.com/~sciencehistory/cautious.htm
I think, at least hope, this is the example followed by most modern theorists. They are probably less confident in their models than it sometimes appears. On the other hand, they have a better feel for where the good 'hunting spots' are than do we.

A very good link! That paper is indicative of the uncertaincies that premier scientists held regarding their own work. Halton Arp wrote to me (nearly 20 years ago) that after viewing Hubble's papers, he saw a similar level of caution in Hubble's work, saying "IF redshift=distance" in Hubble's papers. That was a turning moment for me. We cannot codify the work of astronomers/cosmologists. There is too much left to be done.

 

[Phobos]

i don't know much about physics but what do people mean by 'our universe is expanding' ? thoug we see the truth that no thing is getting larger/longer. what is the proof for this expansion ?
thanx

Just to help clarify the above responses...

(1) It's not just that galaxies are moving away from us (we're not at the center of the universe), it's that space itself is expanding in all directions and the galaxies are being swept apart from each other with that expanding space. We see galaxies moving away from us and observers in a distant galaxy would see other galaxies, including ours, moving away from them. Like one giant expanding loaf of raison bread with no center or edge.

(2) The expansion of space only becomes significant over vast distances (like, inter-galactic distances). So, we do not see things like stars, or planets, or ourselves expanding. Over "shorter" distances (like within a galaxy), gravity/etc. is stronger than the expansion force and stuff stays held together.

(3) The proof is in the redshift of the light reaching us from other galaxies (it's sort of like a Doppler effect) and in the characteristics of the Cosmic Microwave Background radiation (essentially the sizzle left over from the Big Bang).

 

[kronecker]

Thank you turbo and chronos, you both speak very similar language, veery literature, I can't understand all. But very good to read.

Phobo, thanks a liot for that really good and correct (scientific) explanaton, I watched a movie file downloaded from internet a day before posting those questions.

 

[4newton]

Hi just some thoughts.

It is certainly true there is more pressure to churn out new results than to drive another stake into the heart of prospects that appear unlikely to pan out. This approach, of course, assumes the risk of wasting time and resources barking up the wrong tree. On the other hand, the research that is done will eventually force them back onto the right path. If there are serious flaws in the model, it should collapse under its own weight at some point - and hopefully sooner than later.

Scientists, on the whole, tend to do a poor job explaining why they pursue one idea and not others. Their peers understand, and that's about all that matters to them. Unfortunately, the people who end up trying to explain it to the rest of us are lesser experts and occasionally give ambiguous, even bad information. This just fuels the fire, sometimes to the point people think they are being deliberately misled. There are also those who take advantage of this to promote their own agendas. Their motivations range from scamming for profit, feeding their own delusions, or simple puffery. These are the spiders that spin the web of deception. You don't have to google much to find them. Skepticism is your friend.

My experience is that only about 5 in twenty will even consider a new idea unless it carries a known name. Only one in twenty will take the time to understand a new idea. If a known name presents a new idea there is usually a bandwagon that will follow no matter how stupid the idea is.

Educational conditioning prevents most people from ever seeing or deriving a new idea. The worst are people with BS degrees. They have all the interpretations of common theories but no real understanding. Most often they will quote a theory that is opposed to a new idea but never state how or why it is opposed. When pressed they then question your education.

You will find people with a doctor degree much more open to new concepts. Those four years make a lot of difference. The only problem is that you do not find very many of them on this forum. They however have a problem coming out for a new no known name idea because they have a reputation to think of.

The test of a new idea is simple. All you need to do is find one major flaw that is not resolved. Then be careful. The problem with known name ideas is flaws are over looked with the thought that if we just continue with this approach everything will work out. This is the perpetual motion concept, if we make it big enough it will work.

Trust math to say when you are wrong but never trust math to tell you if you are right. Not all things in math are real. Trust unbiased observation. Be careful of an interpretation of an observation. Don’t be limited by your education.