Space.com : Why the Universe is All History

By David Powell Special to SPACE.com posted: 16 October 2007 06:46 am ET

It took 300 years of experiment and calculation to pin down the speed at which light travels in a vacuum: an impressive 186,282 miles per second.

Light will travel slightly slower than this through air, and some wild experiments have actually slowed light to a crawl and seemingly made it go backward, but at the scales encountered in our everyday lives, light is so fast that we perceive our surroundings in real time.

Look up into the night sky and this illusion begins to falter.

"Because light takes time to get here from there, the farther away 'there' is the further in the past light left there and so we see all objects at some time in the past," explains Floyd Stecker of NASA's Goddard Space Flight Center in Greenbelt, Maryland.

Light-years

We see the relatively close moon as it was 1.2 seconds ago and the more distant sun as it was about 8 minutes ago. These measurements—1.2 light-seconds and 8 light-minutes—can be thought to describe both time and distance.

The distance to more remote objects such as other stars is so great it is measured in light-years—the distance light will travel in a year, or about 6 trillion miles (10 trillion kilometers).. Even the nearest star system, Proxima Centauri, lies more than four light-years away, so it appears to us on Earth as it was just over four years ago when the light began its journey.

In this way, light's finite speed gives us a valuable view into the past, and as we strain our gaze deeper into the universe we look further back in time.

"In the case of distant galaxies, we see them as they were billions of years ago when the universe was relatively young," Stecker said.

Out of sight

Some galaxies are so remote that their light hasn't had sufficient time to reach us yet, despite about 13.7 billion years of travel. There could also be more distant objects that will forever remain unknown to us.

"Because the universe is expanding and the expansion appears to be accelerating, there may be distant galaxies which if we can't see them now because their light has not had time to reach us, we will never see," Stecker said.

So we can never see the universe as it is, only as it was at various stages of its development.

To interact with remote parts of the universe—to see them as they are now—would require some exotic means of travel, such as to travel faster than light which, according to Einstein's special theory of relativity, is impossible as it would require an infinite amount of energy.

"The equations of special relativity imply that nothing can go faster then the speed of light in empty space. Therefore, if super-luminal speeds are possible in empty space, they violate the principle of special relativity," Stecker told SPACE.com.

Offbeat theories

There are ways to travel faster than light that do not violate special relativity, but these either outpace light in a transparent medium such as water or do not involve the transmission of information.

To break light speed in space and gain the same easy interaction with the universe that we experience everyday on Earth is a task considered practically impossible even when offbeat theories are considered.

"There are some postulated but unproven theoretical models, inspired by the motivation to unite the quantum theory with the general theory of relativity, which violate special relativity," Stecker said.

These theories involve accelerating particles with mass to super-luminal speeds using ultra high energies. It may also be possible to take a shortcut to distant parts of the universe through a tunnel in space-time known as a wormhole.

"If stable wormholes can exist in space-time and if we can survive traveling through them, then they could provide shortcuts as in the sci-fi movies," Stecker said.

ESA : Science and Galileo - working together

16 October 2007
Galileo is a promising tool for the scientific community, even though it is mainly intended for a set of practical services such as guiding cars, supporting safe aircraft landings or helping blind people to find their way.

This was clearly demonstrated during the first colloquium on scientific and fundamental aspects of the Galileo programme that took place at the 'Cité de l'Espace' in Toulouse from 1 until 4 October. The colloquium was organised by the Air and Space Academy, the Bureau des Longitudes, the Académie de Marine and ESA.

Indeed, the main objective of this world premiere was reached beyond expectations: enhancing the scientific use of Galileo and contributing to the science-based development of Global Navigation Satellite Systems (GNSS).

Around 200 scientists, coming from 25 countries world wide - with 19 being European, gathered and showed their interest in using GNSS systems and in particular Galileo's accuracy and integrity to improve their research in a wide scope that spans Earth sciences (for example: geodesy, meteorology, geophysics), quantum metrology (for example: atomic clocks, inter-satellite links, the Galileo timing system) and relativity (for example: spacetime symmetries, relativistic reference frames, astronomy and GNSS).

At the same time, the scientist's expertise can be of great help in improving the Galileo system itself. This is a 'win-win' situation, since a more precise tool can give more accurate data and therefore improve the measurements needed by the scientists for their research.

The scientists need to have access to GNSS data and ESA will facilitate further access to EGNOS and GIOVE-A data, which are already available to some extent. Dedicated solutions will be found for the scientists, with restrictions only being sometimes applied to commercial or PRS service data. Access to registered, stored data - which are the types most wanted by the scientific community - will be easily granted.

With this conference ESA was also expecting recommendations to improve the system itself and several were expressed so as to ensure the best environment for the scientific exploitation of Galileo. Of course, the requirements are now frozen for the first generation system but within the GNSS evolution programme, supported by ESA member states for technology accompaniment and the new Galileo generation, there is time to implement these particular needs - this is totally open in this programme envelope and new ideas are welcome.

The colloquium also led to reflection on the way the scientific community can organise itself for the use of Galileo. The event complements the already established effort, carried out by ESA, to contact scientific institutes in the fields of timekeeping, frequency standards and geodesy. Following this conference, the Galileo scientific community also includes the domains of quantum metrology and relativistic mechanics.

Although important progress was made, the debate still remain open on how scientists wish to express their specific needs to make the best use of Galileo. This will lead, in the medium and long term, to a privilege working relationship between scientific teams and the project teams responsible for building the next generation of European GNSS.

The colloquium was a great and unique opportunity for the Galileo partners to discover the numerous uses of satellite navigation, in the fields of Earth sciences, quantum metrology and relativistic mechanics, and to identify how scientific requirements can contribute to making the most of the present systems and to define their possible future evolution.

The use of quantum entanglement in the overall GNSS constellation, for example for clock synchronization, and the development of fully relativistic reference frames implemented through the GNSS constellation itself are of particular interest.

ESA : Hubble shows ‘baby’ galaxy is not so young after all

Panning on I Zwicky 18

16 October 2007
The NASA/ESA Hubble Space Telescope has found out the true nature of a dwarf galaxy that was reputed to be one of the youngest galaxies in the Universe.

Astronomers using Hubble have made observations of the galaxy I Zwicky 18 which seem to indicate that it is in fact much older and much farther away than previously thought.

	I Zwicky 18

Observations of I Zwicky 18 at the Palomar Observatory about 40 years ago seemed to show that it was one of the youngest galaxies in the nearby Universe. The studies suggested that the galaxy had erupted with star formation thousands of millions of years after its galactic neighbours, like our galaxy the Milky Way.

Back then it was an important finding for astronomers, since this young galaxy was also nearby and could be studied in great detail - something not easy with observations made across great distances when the universe was much younger.

I Zwicky 18

But the new Hubble data has quashed that possibility. The telescope found fainter, older, red stars contained within the galaxy, suggesting its star formation processes started at least one thousand million years ago and possibly as much as 10 thousand million years ago. The galaxy, therefore, may have formed at the same time as most other galaxies.

“Although the galaxy is not as youthful as was once believed, it is certainly developmentally challenged and unique in the nearby universe,” said astronomer Alessandra Aloisi from the European Space Agency/Space Telescope Science Institute, who led the new study. Spectroscopic observations with ground-based telescopes have shown that I Zwicky 18 is mostly composed of hydrogen and helium, the main ingredients created in the Big Bang. In other words, the stars within it have not created the same amounts of heavier elements as seen in other galaxies nearby.

Zoom in I Zwicky 18

Thus, the galaxy’s primordial makeup suggests that its rate of star formation was much lower than that of other galaxies of similar ages. The galaxy has been studied with most of NASA’s telescopes, including the Spitzer Space Telescope, the Chandra X-ray Observatory, and the Far Ultraviolet Spectroscopic Explorer (FUSE). However, it remains an outstanding mystery as to why I Zwicky 18 formed few stars in the past, and why it is forming so many new stars right now.

	I Zwicky 18

The new Hubble data also suggests that I Zwicky 18 is 59 million light-years from Earth, almost 10 million light-years more distant than previously believed. By extragalactic standards, this is still in our own backyard yet the galaxy’s larger-than-expected distance may now explain why astronomers have had difficulty detecting older, fainter stars within the galaxy until now. In fact, the faint old stars in I Zwicky 18 are almost at the limit of Hubble’s sensitivity and resolution.

Aloisi and her team discerned the new distance by observing blinking stellar distance-markers within I Zwicky 18. Some massive stars, called Cepheid variables, pulse with a regular rhythm. The timing of their pulsations is directly related to their brightness. By comparing their actual brightness with their observed brightness, astronomers can precisely measure their distance.

I Zwicky 18

The team determined the observed brightness of three Cepheids and compared it to the actual brightness predicted by theoretical models specifically tailored for the low metal content of I Zwicky 18 to determine the distance to the galaxy. The Cepheid distance was also validated with another distance indicator, specifically the observed brightness of the brightest red stars in a characteristic stellar evolutionary phase (the so-called ‘giant’ phase).

Cepheid variables have been studied for decades, especially by Hubble, and have been instrumental in the determination of the scale of our universe. This is the first time, however, that variable stars with such few heavy elements were found. This may provide unique new insights into the properties of variable stars, which is now a topic of ongoing study.

Notes for editors:

The Hubble Space Telescope is a project of international cooperation between NASA and ESA.

Aloisi and her team’s results appear in the 1 October issue of the Astrophysical Journal Letters in ‘I Zw 18 Revisited with HST ACS and Cepheids: New Distance and Age’.

Aloisi’s team consists of Francesca Annibali, Jennifer Mack, and Roeland van der Marel of the Space Telescope Science Institute, Marco Sirianni of ESA and Space Telescope Science Institute, Abhijit Saha of the National Optical Astronomy Observatories, and Gisella Clementini, Rodrigo Contreras, Giuliana Fiorentino, Marcella Marconi, Ilaria Musella, and Monica Tosi of the Italian National Astrophysics Institutes in Bologna and Naples.

ESA : Hummocky and shallow Maunder crater

Maunder Crater

16 October 2007
The High Resolution Stereo Camera (HRSC) on ESA’s Mars Express orbiter has obtained pictures of the Noachis Terra region on Mars, in particular, the striking Maunder crater.

The images were taken in orbits 2412 and 2467 on 29 November and 14 December 2005 respectively, with a ground resolution of approximately 15 metres per pixel.

	Noachis Terra context map

Maunder crater lies at 50° South and 2° East, approximately in the center of Noachis Terra. The sun illuminates the scene from the north-east (top left in the image).

The impact crater, named after the british astronomer Edward W. Maunder (1851-1928), is located halfway between Argyre Planitia and Hellas Planitia on the southern Highlands of Mars.

A perspective view of Maunder Crater

With a diameter of 90 kilometres and a depth of barely 900 metres, the crater is not one of the largest impact craters on Mars at present, but it used to be much deeper. It has since been filled partially with large amounts of material.

The west of the crater experienced a major slope failure, during which a large landslide transported loose material eastward, to the inner parts of the crater. The edges of the crater rim that collapsed exhibit gullies which might be associated with the mass transport of the material.

	Maunder Crater, perspective view

The transition zone from the western rim of the crater to the rather smooth crater floor on the eastern edge shows hummocky terrain. Such terrain exhibits small, irregularly-shaped hills and valleys. The hummocky terrain in the Maunder crater was formed by deposition of landslide debris.

In the east, the crater floor is bounded by a trough, approximately 700 metres deep. The trough may be associated with a landslide on the western edge of the crater. Some gullies can be seen on the upper edge of the trough which is possible evidence for water seepage.

Maunder Crater, Noachis Terra

The small, 500 to 2500-metre long, dark features on the crater floor are eye-catching. These features are called Barchan dunes, one of the most abundant dune forms in arid environments. Dunes of this kind are also found on Earth, for example in the West-African Namib desert.

The colour scenes have been derived from the three HRSC-colour channels and the nadir channels. The perspective views have been calculated from the digital terrain model derived from the HRSC stereo channels. The anaglyph image was calculated from the nadir channels and two stereo channels, stereoscopic glasses are required for viewing. The 3-D (anaglyph) picture has been put together from several individual 3-D images of different scenes, enhancing the view over larger areas.

Maunder Crater, Noachis Terra

For more information on Mars Express HRSC images, please read our updated FAQ (frequently asked questions).

Bad Astronomy : Deep Impact interview with Brian Cox

On July 4, 2005, NASA’s Deep Impact mission smacked an 800-pound block of copper into a comet.

That’s pretty cool all by itself. But the science behind the mission was to find out what happens when a comet is hit, what materials a comet is made of, and what materials lie beneath the surface. I wrote a series of posts about the mission (here, here, and here) back when it happened.

I also flew down to LA to do an interview for a British TV show called Star Date. The interviewer was rock star/physicist Brian Cox, and we had a smashing (har har) time talking about how Hollywood portrays asteroid and comet impacts. We sat on the roof of a hotel and chatted about the movie "Deep Impact". After much woe (converting VHS tapes! Converting VOB files! Uploading! Downloading! Fire! Destruction! And I still couldn’t get the frackin’ aspect ratio right), I was finally able to put the interview up on YouTube.

This was just a bit of fun, but it was excellent meeting Brian. I hope to do more with him in the future; I can see we have very similar vision on how science should be presented to the public.

Bad Astronomy : Cassini: 10 years and counting

Has it really been 10 years since the launch of the Cassini Saturn probe?

Wow.

To celebrate the anniversary, NASA has released a whole bunch of cool images and animations. They’re all incredibly beautiful, but how can you resist this one in particular?

[Click the images for much larger versions!]

There’s something about seeing Saturn from a height. Wow again.

I’m also fond of this one:

See the rainbow? In this image, the Sun is directly behind the camera. The sunlight hits the ice particles in the rings and gets refracted back toward you, making a bright spot in the rings. But why the rainbow? At first I thought it was a glory, but actually it’s an illusion! Cassini doesn’t take color images like your digital camera does. It takes a series of images with different filters which are then combined on the ground to produce color. As Cassini swept past this point over the rings, it took three images (red, green, and blue) which were then added together. Since Cassini was moving, the spot smeared out, and since the color images were taken sequentially, we see an elongated rainbow. We can also see yellow and other colors in the rainbow because the spot was big, bigger than the amount it got smeared out by Cassini’s motion. The right part of the spot in one image overlaps the location of the left part of the spot in the next image, so the primary RGB colors add together to get the secondary colors.

Kewlll.

This next one is incredible. It’s an animation of tiny Prometheus and its effect on Saturn’s thin F ring:

[To see this better, click the animation for a larger version.] Prometheus orbits Saturn every 14.7 hours in an ellipse. The top of the ellipse brings it just out to the orbit of the F ring particles. When it gets close, it pulls out a streamer of material. The camera stays centered on the moon, but the overall orbital motion of Prometheus and the ring is to the right. Prometheus, closer to Saturn, moves a little bit faster than the ring particles. As it pulls out the streamer of particles, they fall toward the moon and wind up orbiting Saturn a little faster than they did before. However, they still aren’t moving as quickly as Prometheus, and fall back to the left as the moon leaves them behind. The view is odd since the moon stays centered; if the point of view of the camera were stationary and everything swept past from left to right, it would look different. You’d see the actual elliptical motion of the moon as a big arc from left to right, and the ring particles would be seen moving that direction as well, just not as quickly as the moon does.

It all depends on your POV.

And that, BABloggees, is the whole point. We don’t go to these exotic locations in the solar system because we know everything that’s going on, or because we know what we’ll expect to see. We go because we don’t know. But we also go because we need to have our positions rattled, our notions shaken, our ideas tested. When we see Saturn from above, or co-orbit with a moon, or see a rainbow reflected in particles of ice a billion kilometers away, the only thing we can be sure of is that we’ll see new things, unexpected things.

That’s how we learn. That’s how we grow. And that’s what science does for us.