Scott Alan Johnston (that’s me!) joined the Universe Today team just over a year ago. Since then, I’ve written over 50 space news stories for the website – time flies when you’re having fun! But when I’m not writing articles here on Universe Today, I’m a historian of science, and I recently released a new book about the history of timekeeping.
Have you ever wondered why we tell time the way we do? Well, history buffs, come along for a journey:
HD+ molecular ions (yellow and red pairs of dots: proton and deuteron) suspended in an ultra-high vacuum between atomic ions (blue dots). Credit: HHU / Alighanbari, Hansen, Schiller
To measure small differences in time, you need a really tiny clock, and researchers in Germany have discovered the smallest known clock: a single hydrogen molecule. Using the travel of light across the length of that molecule, those scientists have measured the smallest interval of time ever: 247 zeptoseconds. Don’t know what a “zepto” is? Read on…
The Big Bang Theory: A history of the Universe starting from a singularity and expanding ever since. Credit: grandunificationtheory.com
Ever since Lemaitre and Hubble’s first proposed it in the 1920s, scientists and astronomers have been aware that the Universe is expanding. And from these observations, cosmological theories like the Big Bang Theory and the “Arrow of Time” emerged. Whereas the former addresses the origins and evolution of our Universe, the latter argues that the flow of time in one-direction and is linked to the expansion of space.
For many years, scientists have been trying to ascertain why this is. Why does time flow forwards, but not backwards? According to new study produced by a research team from the Yerevan Institute of Physics and Yerevan State University in Armenia, the influence of dark energy may be the reason for the forward-flow of time, which may make one-directional time a permanent feature of our universe.
Today, theories like the Arrow of Time and the expansion of the universe are considered fundamental facts about the Universe. Between measuring time with atomic clocks, observing the red shift of galaxies, and created detailed 3D maps that show the evolution of our Universe over the course of billions of years, one can see how time and the expansion of space are joined at the hip.
Artist’s impression of the influence gravity has on space time. Credit: space.com
The question of why this is the case though is one that has continued to frustrate physicists. Certain fundamental forces, like gravity, are not governed by time. In fact, one could argue without difficulty that Newton’s Laws of Motion and quantum mechanics work the same forwards or backwards. But when it comes to things on the grand scale like the behavior of planets, stars, and entire galaxies, everything seems to come down to the Second Law of Thermodynamics.
This law, which states that the total chaos (aka. entropy) of an isolated system always increases over time, the direction in which time moves is crucial and non-negotiable, has come to be accepted as the basis for the Arrow of Time. In the past, some have ventured that if the Universe began to contract, time itself would begin to flow backwards. However, since the 1990s and the observation that the Universe has been expanding at an accelerating rate, scientists have come to doubt that this.
If, in fact, the Universe is being driven to greater rates of expansion – the predominant explanation is that “Dark Energy” is what is driving it – then the flow of time will never cease being one way. Taking this logic a step further, two Armenian researchers – Armen E. Allahverdyan of the Center for Cosmology and Astrophysics at the Yerevan Institute of Physics and Vahagn G. Gurzadyan of Yerevan State University – argue that dark energy is the reason why time always moves forward.
In their paper, titled “Time Arrow is Influenced by the Dark Energy“, they argue that dark energy accelerating the expansion of the universe supports the asymmetrical nature of time. Often referred to as the “cosmological constant” – referring to Einstein’s original theory about a force which held back gravity to achieve a static universe – dark energy is now seen as a “positive” constant, pushing the Universe forward, rather than holding it back.
Diagram showing the Lambda-CBR universe, from the Big Bang to the the current era. Credit: Alex Mittelmann/Coldcreation
To test their theory, Allahverdyan and Gurzadyan used a large scale scenario involving gravity and mass – a planet with increasing mass orbiting a star. What they found was that if dark energy had a value of 0 (which is what physicists thought before the 1990s), or if gravity were responsible for pulling space together, the planet would simply orbit the star without any indication as to whether it was moving forwards or backwards in time.
But assuming that the value of dark energy is a positive (as all the evidence we’ve seen suggests) then the planet would eventually be thrown clear of the star. Running this scenario forward, the planet is expelled because of its increasing mass; whereas when it is run backwards, the planet closes in on the star and is captured by it’s gravity.
In other words, the presence of dark energy in this scenario was the difference between having an “arrow of time” and not having one. Without dark energy, there is no time, and hence no way to tell the difference between past, present and future, or whether things are running in a forward direction or backwards.
But of course, Allahverdyan and Gurzadyan were also sure to note in their study that this is a limited test and doesn’t answer all of the burning questions. “We also note that the mechanism cannot (and should not) explain all occurrences of the thermodynamic arrow,” they said. “However, note that even when the dark energy (cosmological constant) does not dominate the mean density (early universe or today’s laboratory scale), it still exists.”
Limited or not, this research is representative of some exciting new steps that astrophysicists have been taking of late. This involves not only questioning the origins of dark energy and the expansion force it creates, but also questioning its implication in basic physics. In so doing, researchers may finally be able to answer the age-old question about why time exists, and whether or not it can be manipulated (i.e. time travel!)
I’m going to ask you how long a day is on Earth, and you’re going to get the haunting suspicion that this is a trap. Your instincts are right, it’s a trap! The answer may surprise you.
How long is a day on Earth? Or more specifically, how long does it take for the Earth to turn once on its axis? For all the stars to move through the sky and return to their original position? Go ahead, and yell your answer answer at the screen… 24 hours?
Wrong! It only takes 23 hours, 56 minutes and 4.0916 seconds for the Earth to turn once its axis. Unless that’s what you said. In which case, congratulations!
I’m sure you’re now stumbling around in an incoherent state, trying to understand how you could have possibly messed this up. Were you reprogrammed by the hidden chronology conspiracy? Have time travellers been setting back all your clocks every day by 4 minutes? How was your whole life a lie?
Here’s the deal. When you consider a day, you’re probably thinking of your trusty clock, or maybe that smartphone lock screen that clearly measures 24 hours.
What you have come to understand as a “day” is classified by astronomers as a solar day. It’s the amount of time it takes for the Sun to move through the sky and return to roughly the same spot.
This is different from the amount of time it takes for the Earth to turn once on its axis – the 23 hours, 56 minutes. Also known as a sidereal day.
Why are these two numbers different? Imagine the Earth orbiting the Sun, taking a full 365 days, 5 hours, 48 minutes and 46 seconds to complete the entire journey. At the same time, the Earth is spinning on its axis.
Each day that goes by, the Earth needs to turn a little further for the Sun to return to the same place in the sky.… And that extra time is about 4 minutes.
If we only measured sidereal days, the position of the Sun would slip back, day after day. For half of the year, the Sun would be up between 12am and 12pm, and for the other half, it would be between 12pm and 12am. There would be no connection between what time it is, and whether or not the Sun is in the sky.
Axis of the Earth’s pole. Credit: NASA / Mysid
Can you imagine teaching your children how to read a clock, and then getting them to multiply that by the calendar to figure out when My Little Pony: Friendship is Magic starts? Madness.
Better to keep them in the dark, teach them that a day is 24 hours, and deny all knowledge when they get a little older, and start to ask you challenging questions. But pedants among you already knew that, didn’t you?
You already knew that a sidereal day is a little shorter than a solar day, and that everyone else has been living a lie. You’re the only one who can read the signs and know the terrifying truth. Aren’t you? Well, I’m here to tell you that you’re wrong too. There’s a deeper conspiracy that you’re not a part of. Dear Pedant, your life is also a lie.
The axis of the Earth’s pole, the imaginary line that you could draw between the south pole and the north pole is currently pointed roughly at Polaris, aka The North Star. But we’re wobbling like a top, and where the axis is pointing is slowly precessing westward over the course of 26,000 years. This means that a sidereal day is actually 0.0084 seconds shorter when you account for this extra movement of the Earth’s axis.
Earthquakes. Credit: USGS / Google Maps / AJAX / SODA
There are other events that can increase or decrease the length of an Earth day. Because of our tidal interactions with the Moon, the length of a day on Earth has increased by about 1.7 milliseconds over the last 100 years. Powerful earthquakes can change the Earth’s rotation time by a few microseconds depending on how the tectonic plates shove around. Even as the glaciers melt, the rotation speed slows down a little more.
So, if someone asks you how long a day is, make sure they clarify whether it’s a solar day or a sidereal day. And then ask if they’d like you to incorporate the Earth’s precession, tidal locking and recent earthquakes into the calculation.
If they give you a knowing nod, congratulations, you’re talking to another member of the vast chronology conspiracy.
When did you discover your whole life was a lie? Tell us in the comments below.
This artist’s impression shows the surroundings of the supermassive black hole at the heart of the active galaxy NGC 3783 in the southern constellation of Centaurus (The Centaur). Credit: ESO/M. Kornmesser
We’ve come a long way in 13.8 billion years; but despite our impressively extensive understanding of the Universe, there are still a few strings left untied. For one, there is the oft-cited disconnect between general relativity, the physics of the very large, and quantum mechanics, the physics of the very small. Then there is problematic fate of a particle’s intrinsic information after it falls into a black hole. Now, a new interpretation of fundamental physics attempts to solve both of these conundrums by making a daring claim: at certain scales, space and time simply do not exist.
Let’s start with something that is not in question. Thanks to Einstein’s theory of special relativity, we can all agree that the speed of light is constant for all observers. We can also agree that, if you’re not a photon, approaching light speed comes with some pretty funky rules – namely, anyone watching you will see your length compress and your watch slow down.
But the slowing of time also occurs near gravitationally potent objects, which are described by general relativity. So if you happen to be sight-seeing in the center of the Milky Way and you make the regrettable decision to get too close to our supermassive black hole’s event horizon (more sinisterly known as its point-of-no-return), anyone observing you will also see your watch slow down. In fact, he or she will witness your motion toward the event horizon slow dramatically over an infinite amount of time; that is, from your now-traumatized friend’s perspective, you never actually cross the event horizon. You, however, will feel no difference in the progression of time as you fall past this invisible barrier, soon to be spaghettified by the black hole’s immense gravity.
So, who is “correct”? Relativity dictates that each observer’s point of view is equally valid; but in this situation, you can’t both be right. Do you face your demise in the heart of a black hole, or don’t you? (Note: This isn’t strictly a paradox, but intuitively, it feels a little sticky.)
And there is an additional, bigger problem. A black hole’s event horizon is thought to give rise to Hawking radiation, a kind of escaping energy that will eventually lead to both the evaporation of the black hole and the destruction of all of the matter and energy that was once held inside of it. This concept has black hole physicists scratching their heads. Because according to the laws of physics, all of the intrinsic information about a particle or system (namely, the quantum wavefunction) must be conserved. It cannot just disappear.
Dr. Stephen Hawking of Cambridge University alongside illustrations of a black hole and an event horizon with Hawking Radiation. He continues to engage his grey matter to uncover the secrets of the Universe while others attempt to confirm his existing theories. (Photo: BBC, Illus.: T.Reyes)
Why all of these bizarre paradoxes? Because black holes exist in the nebulous space where a singularity meets general relativity – fertile, yet untapped ground for the elusive theory of everything.
Enter two interesting, yet controversial concepts: doubly special relativity and gravity’s rainbow.
Just as the speed of light is a universally agreed-upon constant in special relativity, so is the Planck energy in doubly special relativity (DSR). In DSR, this value (1.22 x 1019 GeV) is the maximum energy (and thus, the maximum mass) that a particle can have in our Universe.
Two important consequences of DSR’s maximum energy value are minimum units of time and space. That is, regardless of whether you are moving or stationary, in empty space or near a black hole, you will agree that classical space breaks down at distances shorter than the Planck length (1.6 x 10-35 m) and classical time breaks down at moments briefer than the Planck time (5.4 x 10-44 sec).
In other words, spacetime is discrete. It exists in indivisible (albeit vanishingly small) units. Quantum below, classical above. Add general relativity into the picture, and you get the theory of gravity’s rainbow.
Physicists Ahmed Farag Ali, Mir Faizal, and Barun Majumder believe that these theories can be used to explain away the aforementioned black hole conundrums – both your controversial spaghettification and the information paradox. How? According to DSR and gravity’s rainbow, in regions smaller than 1.6 x 10-35 m and at times shorter than 5.4 x 10-44 sec… the Universe as we know it simply does not exist.
“Say what??” -Albert Einstein
“In gravity’s rainbow, space does not exist below a certain minimum length, and time does not exist below a certain minimum time interval,” explained Ali, who, along with Faizal and Majumder, authored a paper on this topic that was published last month. “So, all objects existing in space and occurring at a time do not exist below that length and time interval [which are associated with the Planck scale].”
Luckily for us, every particle we know of, and thus every particle we are made of, is much larger than the Planck length and endures for much longer than the Planck time. So – phew! – you and I and everything we see and know can go on existing. (Just don’t probe too deeply.)
The event horizon of a black hole, however, is a different story. After all, the event horizon isn’t made of particles. It is pure spacetime. And according to Ali and his colleagues, if you could observe it on extremely short time or distance scales, it would cease to have meaning. It wouldn’t be a point-of-no-return at all. In their view, the paradox only arises when you treat spacetime as continuous – without minimum units of length and time.
“As the information paradox depends on the existence of the event horizon, and an event horizon like all objects does not exist below a certain length and time interval, then there is no absolute information paradox in gravity’s rainbow. The absence of an effective horizon means that there is nothing absolutely stopping information from going out of the black hole,” concluded Ali.
No absolute event horizon, no information paradox.
And what of your spaghettification within the black hole? Again, it depends on the scale at which you choose to analyze your situation. In gravity’s rainbow, spacetime is discrete; therefore, the mathematics reveal that both you (the doomed in-faller) and your observer will witness your demise within a finite length of time. But in the current formulation of general relativity, where spacetime is described as continuous, the paradox arises. The in-faller, well, falls in; meanwhile, the observer never sees the in-faller pass the event horizon.
“The most important lesson from this paper is that space and time exist only beyond a certain scale,” said Ali. “There is no space and time below that scale. Hence, it is meaningless to define particles, matter, or any object, including black holes, that exist in space and time below that scale. Thus, as long as we keep ourselves confined to the scales at which both space and time exist, we get sensible physical answers. However, when we try to ask questions at length and time intervals that are below the scales at which space and time exist, we end up getting paradoxes and problems.”
To recap: if spacetime continues on arbitrarily small scales, the paradoxes remain. If, however, gravity’s rainbow is correct and the Planck length and the Planck time are the smallest unit of space and time that fundamentally exist, we’re in the clear… at least, mathematically speaking. Unfortunately, the Planck scales are far too tiny for our measly modern particle colliders to probe. So, at least for now, this work provides yet another purely theoretical result.
The paper was published in the January 23 issue of Europhysics Letters. A pre-print of the paper is available here.
The Big Bang Theory: A history of the Universe starting from a singularity and expanding ever since. Credit: grandunificationtheory.com
Astronomers are pretty sure what happened after the Big Bang, but what came before? What are the leading theories for the causes of the Big Bang?
About 13.8 billion years ago the Universe started with a bang, kicked the doors in, brought fancy cheeses and a bag of ice, spiked the punch bowl and invited the new neighbors over for all-nighter to encompass all all-nighters from that point forward.
But what happened before that?
What was going on before the Big Bang? Usually, we tell the story of the Universe by starting at the Big Bang and then talking about what happened after. Similarly and completely opposite to how astronomers view the Universe… by standing in the present and looking backwards. From here, the furthest we can look back is to the cosmic microwave background, which is about 380,000 years after the big bang.
Before that we couldn’t hope to see a thing, the Universe was just too hot and dense to be transparent. Like pea soup. Soup made of delicious face burning high energy everything.
In traditional stupid earth-bound no-Tardis life unsatisfactory fashion, we can’t actually observe the origin of the Universe from our place in time and space.
Damn you… place in time and space.
Fortunately, the thinky types have come up with some ideas, and they’re all one part crazy, one part mind bendy, and 100% bananas. The first idea is that it all began as a kind of quantum fluctuation that inflated to our present universe.
Artistic view of a radiating black hole. Credit: NASA
Something very, very subtle expanding over time resulting in, as an accidental byproduct, our existence. The alternate idea is that our universe began within a black hole of an older universe.
I’m gonna let you think about that one. Just let your brain simmer there.
There was universe “here”, that isn’t our universe, then that universe became a black hole… and from that black hole formed us and EVERYTHING around us. Literally, everything around us. In every direction we look, and even the stuff we just assume to be out there.
Here’s another one. We see particles popping into existence here in our Universe. What if, after an immense amount of time, a whole Universe’s worth of particles all popped into existence at the same time. Seriously… an immense amount of time, with lots and lots of “almost” universes that didn’t make the cut.
BICEP2 Telescope at twilight at the South Pole, Antartica (Credit: Steffen Richter, Harvard University)
More recently, the BICEP2 team observed what may be evidence of inflation in the early Universe.
Like any claim of this gravity, the result is hotly debated. If the idea of inflation is correct, it is possible that our universe is part of a much larger multiverse. And the most popular form would produce a kind of eternal inflation, where universes are springing up all the time. Ours would just happen to be one of them.
It is also possible that asking what came before the big bang is much like asking what is north of the North Pole. What looks like a beginning in need of a cause may just be due to our own perspective. We like to think of effects always having a cause, but the Universe might be an exception. The Universe might simply be. Because.
You tell us. What was going on before the party started? Let us know in the comments below.
And if you like what you see, come check out our Patreon page and find out how you can get these videos early while helping us bring you more great content!
Check your watch, what time is it? But wait, you’ve actually been moving and accelerating, and according to Einstein, everything’s relative. So what time is it really? It all depends…
Flavor Flav knows what time it is. At least he does for Flavor Flav. Even with all his moving and accelerating, with the planet, the solar system, getting on planes, taking elevators, and perhaps even some light jogging. In the immortal words of Kool Moe Dee. Do you know what time it is?
Didn’t Einstein tell us it’s all relative? Does anyone actually know what time it is? I mean, aside from figuratively, or in a political sense, or perhaps as part of rap performance from whence the power is being fought from, requiring the sick skills of a hype man wearing a clock around his neck on a big chain.
So, after all my fancy dancing and longing for a time in rap and hip hop from days gone by, I must present to you “faithful audience member” an answer in the form of your 3 least favorite words I get to deliver.
It all depends…
You have heard that everything is relative, usually we hear it from people who like to talk about “connections on many different levels”, which is just nonsense.
But in physics “everything” is relative in a very particular way. Everything is relative to the speed of light, which is the same in every reference frame. Which is confusing and repeated enough that it can become meaningless.
So I’m going to do my best to explain it. If I shine a flashlight in front of me, I will measure the beam to travel at about 300,000 km/s, which is also known as the speed of light.
And if you are moving at 200,000 km/s faster than me, and shine a flashlight ahead of you, I will see the light from your flashlight moving at the 300,000km/s. It will appear to me, as though the light from your flashlight is moving away from you at 100,000 km/s.
But when you will measure the speed of that light, relative to you, you’d think it’d be moving at 100,000 km/s as well, but instead from your perspective it will ALSO clock in at 300,000 km/s.
Artist’s impression – General Relativity.
The speed of light. How is this even possible? It is possible in part because the rate at which you experience time relative to me changes. For you, time will seem normal, but from my perspective your time will seem slower. We agree on how fast light is moving in kilometers per second, but we disagree how long a second is. We also, by the way, disagree on the length of a meter.
This seems strange because we imagine that space and time are absolute things, and light is something that travels through space. This is our experience. Suggesting things like time and space are malleable values at best is unsettling and at worst will make us nanners from thinking too much about.
Hold on to your tinfoil hats, for it is in fact light that is the absolute, and space and time are relative to it. So what time it is depends upon your vantage point, and so there is no single absolute time.
Finally, because of relativity, each point in the Universe experiences time at a slightly different rate. For example, when we observe the cosmic microwave background, we find that we are moving at a speed of about 630 km/s relative to the background. That means we experience time a bit more slowly that something at rest relative to the cosmic background.
It’s just a tiny bit slower, but added over the entire age of the Universe, our cosmic clock is 30,000 years behind the times. Feel free to set your watch. But don’t get too precise about it. Your time could be off by tens of thousands of years.
What about you? What’s your favorite way to explain special relativity to someone. Tell us in the comments below.
Have you ever noticed that time flies when you’re having fun? Well, not for light. In fact, photons don’t experience any time at all. Here’s a mind-bending concept that should shatter your brain into pieces.
As you might know, I co-host Astronomy Cast, and get to pick the brain of the brilliant astrophysicist Dr. Pamela Gay every week about whatever crazy thing I think of in the shower. We were talking about photons one week and she dropped a bombshell on my brain. Photons do not experience time. [SNARK: Are you worried they might get bored?]
Just think about that idea. From the perspective of a photon, there is no such thing as time. It’s emitted, and might exist for hundreds of trillions of years, but for the photon, there’s zero time elapsed between when it’s emitted and when it’s absorbed again. It doesn’t experience distance either. [SNARK: Clearly, it didn’t need to borrow my copy of GQ for the trip.]
Since photons can’t think, we don’t have to worry too much about their existential horror of experiencing neither time nor distance, but it tells us so much about how they’re linked together. Through his Theory of Relativity, Einstein helped us understand how time and distance are connected.
Let’s do a quick review. If we want to travel to some distant point in space, and we travel faster and faster, approaching the speed of light our clocks slow down relative to an observer back on Earth. And yet, we reach our destination more quickly than we would expect. Sure, our mass goes up and there are enormous amounts of energy required, but for this example, we’ll just ignore all that.
If you could travel at a constant acceleration of 1 g, you could cross billions of light years in a single human generation. Of course, your friends back home would have experienced billions of years in your absence, but much like the mass increase and energy required, we won’t worry about them.
The closer you get to light speed, the less time you experience and the shorter a distance you experience. You may recall that these numbers begin to approach zero. According to relativity, mass can never move through the Universe at light speed. Mass will increase to infinity, and the amount of energy required to move it any faster will also be infinite. But for light itself, which is already moving at light speed… You guessed it, the photons reach zero distance and zero time.
Photons can take hundreds of thousands of years to travel from the core of the Sun until they reach the surface and fly off into space. And yet, that final journey, that could take it billions of light years across space, was no different from jumping from atom to atom.
There, now these ideas can haunt your thoughts as they do mine. You’re welcome. What do you think? What’s your favorite mind bending relativity side effect? Tell us in the comments below.
An illustration showing how a sailboat mission to Titan might land and become operational. Copyright: Estevan Guzman for Universe Today.
The large moons orbiting the gas giants in our solar system have been getting increasing attention in recent years. Titan, Saturn’s largest moon, is the only natural satellite known to house a thick atmosphere. It’s surface, revealed in part by the Cassini probe, is sculpted by lakes and rivers. There is interest in exploring Titan further, but this is tricky from orbit because seeing through the thick atmosphere is difficult. Flying on Titan has been discussed around the web (sometimes glibly), and this was even one of the subjects treated by the immensely popular comic, XKCD.
However, there remains the problem of powering propulsion. The power requirements for flight are quite minimal on Titan, so solar wings might work. But Titan also presents an alternative: sailing.
Images from the Cassini mission show river networks draining into lakes in Titans north polar region. Credit: NASA/JPL/USGS.
With all those lakes and rivers, exploring Titan with a surface ship might be a great way to see much of the moon. The vehicle wouldn’t be sailing on water, though. The lakes on Titan are composed of liquid methane. The challenge is therefore making the vessel buoyant: liquid methane is only 45% as dense as liquid water. This means we would need a lot of displacement. A deep, hollow hull could do this, however, and it turns out that the liquid methane has an advantage that helps make up for the low density: it is much less viscous than water.
Reynolds number is proportional to the ratio of density to viscosity, and it turns out that friction drag on a hull is inversely proportional to Re. While Titan’s seas and lakes have only 45% the density of water, they also have only 8% of the viscosity. This means that the Titan sailing vessel would only experience about 26% of the friction drag as its Earth equivalent. [Yacht designers have found that the friction drag is about equal to 0.075/(log(Re)-2)^2)]. That leaves us room to make the hull deeper (important to compensate for the density as above), and longer (if we want a longer waterline, which will make the bow waves longer and improve maximum speed).
The sail itself would get less wind, on average, on Titan than Earth. Average wind speeds on Titan seem to be about 3 meters/s, according to Cassini, though it might be higher over the lakes. Average wind speed over Earth oceans is closer to 6.6 meters/s. But, the Titan atmosphere is also about 4x denser than Earth’s, and both lift and drag are proportional to fluid density. All told, this means that the total fluid force on the sail will be about 83% of what you’d get on Earth, all else being equal, which could be sufficient. There would be a premium on sail efficiency and size, and so we might have to take advantage of the low-friction hull to examine shapes with more stability that can house a larger, taller (and presumably high aspect ratio) sail.
This is all quite speculative, of course, but it provides a fun exercise and perhaps provides inspiration as we imagine tall-sailed robotic vessels silently cruising the lakes of Titan.
But with all the recent discoveries on Titan by the Cassini spacecraft — things like lakes, seas, rivers and weather and climate patterns that create both fog and rain — a mission like this will be given more consideration in the future.
Hubble mosaic of massive galaxy cluster MACS J0717.5+3745, thought to be connected by a filament of dark matter. Credit: NASA, ESA, Harald Ebeling (University of Hawaii at Manoa) & Jean-Paul Kneib (LAM)
Even though teams of scientists around the world are at this very moment hot on the trail of dark matter — the “other stuff” that the Universe is made of and supposedly accounts for nearly 80% of the mass that we can’t directly observe (yet) — and trying to quantify exactly how so-called “dark energy” drives its ever-accelerating expansion, perhaps one answer to these ongoing mysteries is maybe they don’t exist at all.
This is precisely what one astronomer is suggesting in a recent paper, submitted Dec. 3 to Astrophysical Journal Letters.
In a paper titled “An expanding universe without dark matter and dark energy” (arXiv:1212.1110) Pierre Magain, a professor at Belgium’s Institut d’Astrophysique et de Géophysique, proposes that the expansion of the Universe could be explained without the need for enigmatic material and energy that, to date, has yet to be directly measured.
In addition, Magain’s proposal puts a higher age to the Universe than what’s currently accepted. With a model that shows a slower expansion rate during the early Universe than today, Magain’s calculations estimate its age to be closer to 15.4 – 16.5 billion years old, adding a couple billion more candles to the cosmic birthday cake.
The benefit to a slightly older Universe, Magain posits, is that it’s not so uncannily close to the apparent age of the most distant galaxies recently found — such as MACS0647-JD, which is 13.3 billion light-years away and thus (based on current estimates, see graphic at right) must have formed when the Universe was a mere 420 million years old.
Using accepted physics of how time behaves based on Einstein’s theory of general relativity — namely, how the passage of time is relative to the position and velocity of the viewer (as well as the intensity of the gravitational field the viewer is within) — Magain’s model allows for an observer located within the Universe to potentially be experiencing a different rate of time than a hypothetical viewer located outside the Universe. Not to be so metaphysical as to presume that there are external observers of our Universe but merely to say that an external point would be a fixed one against which one could benchmark a varying passage of time inside the Universe, Magain calls this universal relativity.
A viewer experiencing universal relativity would, Magain claims, always measure the curvature of the Universe to be equal to zero. This is what’s currently observed, a “flatness problem” that Magain insinuates is strangely coincidental.
By attributing an expanding Universe to dark energy and the high velocities of stars along the edges of galaxies (as well as the motions of galaxy clusters themselves) to dark matter, we may be introducing ad hoc elements to the Universe, says Magain. Instead, he proposes his “more economical” model — which uses universal relativity — explains these apparently accelerating, increasingly expanding behaviors… and gives a bigger margin of time between the Big Bang and the formation of the first galactic structures.
There’s quite a bit of math involved, and since I never claimed to understand physics equations you can check out the original paper here.
While intriguing, the bottom line is that dark energy and dark matter have still managed to elude science, existing just outside the borders of what can be observed (although the gravitational lensing effects of what’s thought to be dark matter filaments have been observed by Hubble) and Magain’s paper is merely putting another idea onto the table — one that, while he recognizes needs further testing and relies upon very specific singular parameters, doesn’t depend upon invisible, unobservable and mysteriously dark “stuff”. Whether it belongs on the table or not will be up to other astrophysicists to decide.
Prof. Magain’s research was supported by ESA and the Belgian Science Policy Office.
At right: Artist’s impression of dark matter (h/t to Steve Nerlich)
Note: this is “just” a submitted paper and has not been selected for publication yet. Any hypotheses proposed are those of the author and are not endorsed by this site. (Personally I like dark matter. It’s fascinating stuff… even if we can’t see it. Want an astrophysicist’s viewpoint on the existence of dark matter? Check out Ethan Siegel’s blog response here.)
