Cosmos 250 x Visible Universe

[KanadaHye]

New Model Says the Cosmos Is At Least 250 Times Larger Than the Visible Universe

How big is the universe anyhow? We know the universe is roughly 4 billion years old (14 billion???) and we know how far light travels in a year, so ostensibly it would seem the visible universe is contained to a radius of 14 billion light years. But we know that photons in the cosmic microwave background have traveled some 45 billion light years to reach earth (because the universe is also expanding the most distant visible objects are actually further than 14 billion light years), giving the universe an apparent diameter of at least 90 billion light years.

So how big is it really? A new mathematical analysis says its at least 250 times larger than the visible universe. Which is really, really big.

But it’s not actually the biggest proposed size of the universe. When cosmologists crunch their data, they use different models to give values to the universe’s curvature and therefore it’s size. Since we don’t know the shape of the universe, or whether it’s flat or open or closed or infinite, so we use different benchmarks to make our best guesses. This leads to a huge range of values assigned to the size of the universe, each as un-provable as the last.

So Mihran Vardanyan at Oxford and a few of his colleagues did what outwardly seems obvious but is actually quite difficult: they averaged the results of all this data in the easiest way they could. Using a complex mathematical technique called Bayesian model averaging they found a way to constrain the complexity of the individual models themselves in a way that is much stricter than the constraints on the models themselves. In other words, Bayesian model averaging itself is complex, but it produces a simplified solution from complex models.

What is that simple solution? They found that the curvature of the universe is strictly constrained near a zero value, meaning the universe is likely flat. It’s also at least 250 times bigger than the Hubble volume, which is roughly the size of the visible universe.

Elegance in simplicity; what’s not to like? If you require more complexity, Vardanyan and company’s paper can be found at arXiv.

http://www.popsci.com/science/articl...sible-universe

[armeniyan]

Re: Cosmos 250 x Visible Universe


Mihran Vardanyan and George Smoot (2006 Physics Nobel Prize Winner for his work on COBE, CMB experiment ), Cambridge, UK


Mihran Vardanyan and Martin Lewis Perl (1995 Physics Nobel Prize Winner for discovery of the tau lepton), Blois, France

Daily Mail

It's the question that cosmologists have been asking for decades - just how big is the universe?

The commonly-held belief is that the universe was created by the Big Bang about 13.7billion years ago.

But now scientists believe it is at least 250 times bigger than the visible universe.

Researchers at Oxford University and Imperial College London focused on measuring the curvature of the universe.

Should it be flat or open then the universe must be infinite, but if it is closed like a sphere then it has to be of limited size.

Lead researcher Mihran Vardanyan and his team have come up with a new complex method of analysing all previous research they call the Bayesian method.

Instead of asking how different models of the universe fit the data, they asked how likely, given the data, are the different models to be correct.

One main source of data they used was measuring the size of waves in the early universe that became frozen in the cosmic microwave background - or baryonic acoustic oscillations - using telescopes in space.

Using this method they found that the most likely model is a tightly constrained curvature of the universe - which means it's flat.

It’s also at least 250 times bigger than the Hubble volume, which is approximately the size of the visible universe.

Dr Vardanyan said: 'We demonstrated how the initial assumptions can affect the analysis.

'Using modern astronomers’ assumptions, which favour a flat universe, this gives
98 per cent probability that the universe is indeed flat.

'However, we also did this calculation starting from more relaxed initial assumptions, the probability changed to about 46 per cent, making a flat universe far less probable.

'In this case it also become harder to distinguish between the models.'

Scientists recently worked out the size of the visible universe using data collected by Hubble.

Last week, astronomers discovered the oldest and most distant object in the universe - a galaxy so far away that its light has taken 13.2billion years to reach Earth.

The cluster of stars, dust and gas was spotted by Hubble as it orbited Earth.

The galaxy is so remote, scientists are observing it at a time when the universe was in its infancy, just 480million years after the Big Bang.

http://www.dailymail.co.uk/sciencetech/article-1352959/Cosmos-250-times-bigger-visible-universe-according-scientists.html

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MIT Technology Review (http://www.technologyreview.com/blog/arxiv/26333/)

Cosmos At Least 250x Bigger Than Visible Universe, Say Cosmologists

The universe is much bigger than it looks, according to a study of the latest observations.


When we look out into the Universe, the stuff we can see must be close enough for light to have reached us since the Universe began. The universe is about 14 billion years old, so at first glance it's easy to think that we cannot see things more than 14 billion light years away.

That's not quite right, however. Because the Universe is expanding, the most distant visible things are much further away than that. In fact, the photons in the cosmic microwave background have travelled a cool 45 billion light years to get here. That makes the visible universe some 90 billion light years across.

That's big but the universe is almost certainly much bigger. The question than many cosmologists have pondered is how much bigger. Today we have an answer thanks to some interesting statistical analysis by Mihran Vardanyan at the University of Oxford and a couple of buddies.

Obviously, we can't directly measure the size of the universe but cosmologists have various models that suggest how big it ought to be. For example, one line of thinking is that if the universe expanded at the speed of light during inflation, then it ought to be 10^23 times bigger than the visible universe.

Other estimates depend on a number factors and in particular on the curvature of the Universe: whether it is closed, like a sphere, flat or open. In the latter two cases, the Universe must be infinite.

If you can measure the curvature of the Universe, you can then place limits on how big it must be.

It turns out that in recent years, astronomers have various ingenious ways of measuring the curvature of the Universe. One is to search for a distant object of known size and measure how big it looks. If it's bigger than it ought to be, the Universe is closed; if it's the right size, the universe is flat and if it's smaller, the Universe is open.

Astronomers know of one type of object that fits the bill: waves in the early universe that became frozen in the cosmic microwave background. They can measure the size of these waves, called baryonic acoustic oscillations, using space observatories such as WMAP.

There are also other indicators, such as the luminosity of type 1A supernovas in distant galaxies.

But when cosmologists examine all this data, different models of the Universe give different answers to the question of its curvature and size. Which to choose?

The breakthrough that Vardanyan and pals have made is to find a way to average the results of all the data in the simplest possible way. The technique they use is called Bayesian model averaging and it is much more sophisticated than the usual curve fitting that scientists often use to explain their data.

A useful analogy is with early models of the Solar System. With the Earth at the centre of the Solar System, it gradually became harder and harder to fit the observational data to this model. But astronomers found ways to do it by introducing ever more complex systems, the wheels-within-wheels model of the solar system.

We know now that this approach was entirely wrong. One worry for cosmologists is that a similar process is going on now with models of the Universe.

Bayesian model averaging automatically guards against this. Instead of asking how well the model fits the data, its asks a different question: given the data, how likely is the model to be correct. This approach is automatically biased against complex models--it's a kind of statistical Occam's razor.

In applying it to various cosmological models of the universe, Vardanyan and co are able to place important constraints on the curvature and size of the Universe. In fact, it turns out that their constraints are much stricter than is possible with other approaches.

They say that the curvature of the Universe is tightly constrained around 0. In other words, the most likely model is that the Universe is flat. A flat Universe would also be infinite and their calculations are consistent with this too. These show that the Universe is at least 250 times bigger than the Hubble volume. (The Hubble volume is similar to the size of the observable universe.)

That's big, but actually more tightly constrained than many other models.

And the fact that it comes from such an elegant statistical method means this work is likely to have broad appeal. If so, it may well end up being used to fine tune and constraint other areas of cosmology too.

Ref: arxiv.org/abs/1101.5476: Applications Of Bayesian Model Averaging To The Curvature And Size Of The Universe

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Also in Russian <<Популярная механика>> (http://www.technologyreview.com/blog/arxiv/26333/)


Вселенная может оказаться намного больше, чем ее видимая часть – по некоторым данным, примерно в 250 раз.



Легко заметить, что когда мы вглядываемся в звездное небо, даже с самой мощной аппаратурой, мы способны обозреть ее лишь на таком расстоянии, которое свет способен преодолеть с момента появления Вселенной. Иначе говоря, примерно на 14 млрд. световых лет. На самом деле, все несколько сложнее. Поскольку Вселенная расширяется, и скорость этого расширения все нарастает, самые дальние из видимых нам объектов расположены намного дальше этой границы.

К примеру, фотонам древнейшего реликтового излучения понадобится уже 45 млрд. лет, чтобы добраться до нас из той области, где они находятся сейчас. Получается, что в поперечнике видимая Вселенная достигает уже примерно 90 млрд. световых лет. Это огромная цифра, но мир наверняка еще намного больше – вопрос лишь в том, насколько. Интересный анализ этого вопроса представили недавно оксфордские ученые во главе с Михраном Варданяном (Mihran Vardanyan).

Конечно, никаких непосредственных измерений реального размера Вселенной провести невозможно, но космологи выстраивают различные модели и смотрят, насколько сделанные на их основе выводы согласуются с известной картиной мира. Различные расчеты исходят из разного набора факторов и по-разному оценивают неизвестные пока величины – такие, как форма и кривизна Вселенной (немного подробнее этот увлекательный вопрос мы разбирали в заметках «Плоский мир» и «Бублик мира»).

По разным мнениям, Вселенная может быть плоской, иметь открытую структуру или закрытую. В первых двух случаях размеры ее бесконечны в полном смысле этого слова. Но если она закрыта – скажем, имеет форму сферы или тора – то вопрос о ее конечных размерах вполне уместен.

За последние годы предложено немало довольно остроумных решений этого вопроса. Например, найти как можно более далекий объект известного размера и сравнить с его видимыми размерами: если он окажется крупнее, Вселенная имеет закрытую структуру, если меньше – открытую, если ровно нужную – то она плоская. Поразительно, но нам известны подходящие на эту роль объекты.

Речь о барионных акустических осцилляциях, существование которых еще в 1960-х предсказал академик Сахаров. Они представляют собой акустические колебания, возникавшие в первичной плазме, когда Вселенной было около сотни тысяч лет от роду, и следы их можно выявить в флуктуациях температуры реликтового излучения. Еще одним «стандартом» для этой цели может выступить светимость сверхновых типа Ia в самых удаленных галактиках. Однако когда ученые проводят расчеты с использованием акустических осцилляций или сверхновых, им никак не удается согласовать полученные результаты. Разные работы приводят к разным формам Вселенной и разной ее кривизне.

Лишь теперь Мигран Варданян с коллегами предложили способ «усреднить» результаты с помощью довольно изощренных математических подходов. Главное – вместо того, чтобы подбирать хитрую модель, максимально подходящую под имеющиеся данные, ученые подошли к проблеме с другой стороны: исходя из накопленных данных, какова вероятность верности имеющейся модели?

Разъяснить ситуацию можно на примере эволюции представлений о строении Солнечной системы. Сначала торжествовала геоцентрическая модель, в которой все объекты вращаются вокруг Земли. Однако по мере накопления все более точных данных их все труднее было согласовать с этими взглядами. Появились крайне изощренные подходы, включая эпициклы. Теперь мы знаем, что эти решения были неверны – но, возможно, в такие же точно излишние «дебри» залезают и космологи, пытаясь построить модель структуры Вселенной, но не видя чего-то главного в ней.

Применив новый подход к различным космологическим моделям, Варданян и его коллеги пришли к ряду довольно строгих ограничений, накладываемых на размеры и кривизну Вселенной. Намного более строгих, нежели при альтернативных подходах. По их данным, кривизна должна быть либо нулевой (плоская Вселенная), либо очень близка к нулю, причем тогда в поперечнике ее размеры должны составлять минимум 250 сфер Хаббла - то есть, размеров видимой Вселенной.

[Haykakan]

Re: Cosmos 250 x Visible Universe

If the universe is infinite then why is it tightly constrained? This to me does not sound right.

[kvperos]

Re: Cosmos 250 x Visible Universe

Well this is very complicated physics and statistics. The review above was written so 5th grader could understand it, and doesn't represent accurate information. The article actually says that by measuring the curvature of the universe we can answer the long standing questions about its size. So the analysis they did shoes that a) How useful the statistical technique is b) if you apply it to our Universe you will be able to constrain it's size. However, this final conclusion said that this shows that the universe is infinite and flat.
However if it still has a size (the curvature is spherical) it should be bigger then 200 billion light years wide....

[KanadaHye]

Re: Cosmos 250 x Visible Universe

Fresh evidence for expanding universe

The universe really is expanding and it's not an illusion as a competing theory suggests, say astronomers using NASA's Hubble Space Telescope.

"We are using the new camera on Hubble like a policeman's radar gun to catch the universe speeding," Adam Riess, a professor of physics and astronomy at Johns Hopkins University in Baltimore, said in a NASA release.

Riess said his team was able to look at more stars than ever before in both visible and near-infrared wavelengths of light. He says this allowed him to eliminate errors introduced in previous work, which compared measurements from different telescopes.

The new measurements are thanks to the Wide Field Camera 3, recently installed on the space telescope.

Riess's work gives new evidence that the universe is in fact expanding at an increasing rate because it is filled with a dark energy that works in opposition to gravity. Dark energy is a type of energy that astronomers believe permeates all space.

NASA says Riess's findings rule out an alternate theory of the nature of dark energy. That alternate theory is based on the notion that an enormous bubble of relatively empty space eight billion light-years across surrounds our galactic neighbourhood.

It suggests that because the bubble has a lower density, it expands faster than the more massive universe around it.

"To an observer inside the bubble, it would appear that a dark-energy-like force was pushing the entire universe apart," according to NASA's explanation of what it says is a now debunked theory. "The bubble hypothesis requires that the universe’s expansion rate be much slower than astronomers have calculated, about 60 to 65 kilometres per second per megaparsec."

According to the space agency, Riess's more precise measurements show the expansion rate is 73.8 kilometres per second per megaparsec. A megaparsec is a unit of measure for distances in intergalactic space.

"It looks more like it's dark energy that's pressing the gas pedal," said Riess.

The Hubble Space Telescope has provided unprecedented views of the universe from an altitude of 569 kilometres since it was launched in 1990.

Riess's results appear in the April 1 issue of The Astrophysical Journal.

http://www.cbc.ca/news/technology/st...expansion.html

[KanadaHye]

Re: Cosmos 250 x Visible Universe

If the universe is infinite then why is it tightly constrained? This to me does not sound right.

I agree, everything is in perfect equilibrium from the point of view of our planet. I think of it like this. If the universe is expanding and it's fighting forces of gravity to do so, it's either the universe would eventually break apart in destruction or gather itself and start decreasing in size like a yo-yo and it would do this repeatedly in cycles. If this was the case and there was no external forces to push or pull then it would eventually lose momentum and stabilize.