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Measuring the Hubble Constant Better

kdawson posted more than 5 years ago | from the masing-galaxies dept.

Space 102

eldavojohn writes "The Hubble Constant is used for many things in astrophysics: from determining how fast things are moving away from us, to the total volume of the universe, to predicting how our universe will end. The current best value for the Hubble Constant is 74.2 ± 3.6 (km/s)/Mpc according to recent conventional methods and the recently restored Hubble Telescope. Most astronomers agree that that's within 10% of its actual value. Researchers now claim that they might be able to get to 3% using water molecules in galactic disks to act as masers that amplify radio waves, to analyze galaxies seven times as far away as the current measurements. The further away the 'standard candle' is, the more assured they can be that local effects are not skewing the measurements. From one of the researchers: 'We measured a direct, geometric distance to the galaxy, independent of the complications and assumptions inherent in other techniques. The measurement highlights a valuable method that can be used to determine the local expansion rate of the universe, which is essential in our quest to find the nature of dark energy.' Once the Square Kilometer Array is completed, they hope to get even closer to the actual value."

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In related news (-1, Offtopic)

Anonymous Coward | more than 5 years ago | (#28269839)

Pi is exactly equal to 3!

Linux is why the Hubble Telescope failed (0, Troll)

linustorvaldsisaturd (1573171) | more than 5 years ago | (#28269899)

Linux just isn't ready for the space telescope yet. It may be ready for the web servers that you nerds use to distribute your TRON fanzines and personal Dungeons and Dragons web-sights across the world wide web, but the average space telescope user isn't going to spend months learning how to use a CLI and then hours compiling packages so that they can get a workable graphic interface to check the stars with, especially not when they already have a Windows space telescope that does its job perfectly well and is backed by a major corporation, as opposed to Linux which is only supported by a few unemployed nerds living in their mother's basement somewhere. The last thing I want is a level 5 dwarf (haha) providing me my OS.

fp (-1, Offtopic)

Anonymous Coward | more than 5 years ago | (#28269841)

fp

Re:fp (-1, Offtopic)

Anonymous Coward | more than 5 years ago | (#28270527)

only if fp==fail post

Hubble constant now a misnomer (3, Interesting)

Omnifarious (11933) | more than 5 years ago | (#28269855)

From what I know, it's been discovered in the past decade or so to not be a constant. The expansion of the universe is accelerating. This is a minor nitpick, I know. :-)

Re:Hubble constant now a misnomer (5, Funny)

American Expat (1393429) | more than 5 years ago | (#28269959)

It's just obeying the first rule of computer science: Constants aren't
(second rule: Variables won't)

Re:Hubble constant now a misnomer (1)

davester666 (731373) | more than 5 years ago | (#28271197)

Didn't they already figure out how they screwed up creating the Hubble telescopes main mirror? Or is the mirror warping now?

And didn't they just do the last fix on it just last month?

Re:Hubble constant now a misnomer (2, Informative)

OeLeWaPpErKe (412765) | more than 5 years ago | (#28270151)

Doesn't this constant place an additional limit on the size of the universe (or at least the part of the universe we're ever going to see) ?

c / 74.2 km/s * Mpc = 300000 / 74.2 * 3 261 636.26 lightyear (1 Mpc = 3 261 636.26) or about 1.31872075 Ã-- 10^10 lightyear, about 13 billion lightyear.

Because at that distance, the stars would be moving away from us at light speed, so in reality there's an event horizon between us and stars at that distance. Light from stars further away would never reach us, due to it having unlimited redshift.

As you can see, if the hubble constant becomes bigger, the universe shrinks. If it lowers, the universe becomes bigger.

no, that's not right (1)

Khashishi (775369) | more than 5 years ago | (#28270835)

Universe expansion will create causal separation in the future, but not the past. It doesn't limit how far away you can see something, because you are looking at something in the past, but it does prevent you from going there. Because looking backward in time, the universe is shrinking, and you can see more and more of the universe going back. Looking forward in time, everything is getting more separated, and, for far regions of space, the rate of separation is higher than light can catch up to.

In the scenario of big rip, the acceleration of the expansion continues to increase until the future light cone of every particle is separated from the future light cone of every other particle. The past light cones still intersect.

Re:no, that's not right (2, Funny)

BizzyM (996195) | more than 5 years ago | (#28271185)

Universe expansion will create causal separation in the future, but not the past. It doesn't limit how far away you can see something, because you are looking at something in the past, but it does prevent you from going there. Because looking backward in time, the universe is shrinking, and you can see more and more of the universe going back. Looking forward in time, everything is getting more separated, and, for far regions of space, the rate of separation is higher than light can catch up to.

You just blew my mind

Re:no, that's not right (0)

OeLeWaPpErKe (412765) | more than 5 years ago | (#28276727)

ing back. Looking forward in time, everything is getting more separated, and, for far regions of space, the rate of separation is higher than light can catch up to.

This can only be if there are (massive) regions of space moving faster than light, relative to us.

That an entire galaxy would get accelerated to even a small percentage of light speed is hard enough to believe, but even something like 50% light speed cannot be the speed of a galaxy. Just think of the energy required to accelerate it. FTL is supposed to be impossible, and no respectable scientist can seriously believe that there are so many galaxies moving faster than light, right ?

Also if the hubble constant is universal (the same in other galaxies) you would pretty much require a fourth dimension (other than time, so I guess a fifth), to explain such an effect.

Wouldn't it be a (lot) more simple to explain if there was some sort of cosmic mirror somewhere, that, due to the finite speed of light does not show us a perfect reflection, but rather an ancient reflection ?

Also I was more thinking about the astonishing coincidence. Surely the age of the universe is not calculated using the hubble constant ? That would make it, at best, a wildly inaccurate guess.

Re:no, that's not right (1)

naam00 (1145163) | more than 5 years ago | (#28278105)

ing back. Looking forward in time, everything is getting more separated, and, for far regions of space, the rate of separation is higher than light can catch up to.

This can only be if there are (massive) regions of space moving faster than light, relative to us.

That an entire galaxy would get accelerated to even a small percentage of light speed is hard enough to believe, but even something like 50% light speed cannot be the speed of a galaxy. Just think of the energy required to accelerate it. FTL is supposed to be impossible, and no respectable scientist can seriously believe that there are so many galaxies moving faster than light, right ?

It's somewhat more subtle than that. The galaxy isn't 'racing through space', space itself is expanding -- between us and the galaxy mostly, since galaxies tends to stick together due to gravitation.

This can be, over long distances, percieved to happen at a FTL rate, though nothing is actually moving at that rate. And relatively speaking, that FTL galaxy is unmeasurable, since you will never see it racing away from you.

Re:no, that's not right (1)

OeLeWaPpErKe (412765) | more than 5 years ago | (#28305671)

This can be, over long distances, percieved to happen at a FTL rate, though nothing is actually moving at that rate. And relatively speaking, that FTL galaxy is unmeasurable, since you will never see it racing away from you.

That's very useful since Einsteins equations do not deal with moving at infinite velocity, that is perfectly possible according to Einstein's relativity. It's just that as you accelerate further time would speed up, and you would still arrive at the point in time you would have arrived when flying at light speed. Relatively deals with how said infinite velocity is perceived by others in other reference frames.

So perhaps I was a bit less than thorough. Nothing can be perceived to be moving faster than light either, according to relativity. A perception of an object moving faster than light is a direct violation of einstein's equations.

FTL movement, if you calculate how it would look, would also look very, very different from how these galaxies look. Suppose a ship were to fly away from you, and accelerate to an FTL velocity. At that point the ship would disappear entirely from your vision, to be replaced with an image of the ship decelerating below lightspeed, at the location it drops below FTL speeds.

Then that image would move towards you, OPPOSITE to the actual movement of the ship. The redshift would also be reversed from it's normal appearance into a blueshift effect. A very strong blueshift effect.

If these galaxies were to have a velocity faster than light, even if it's merely appearance, their redshift would reverse, and would their movement vector appear to turn around. Our telescopes should be telling us they're flying toward us at very large speeds.

Obviously that's not happening. They are not flying at FTL speeds, and they are not appearing to fly at FTL speeds either.

Re:Hubble constant now a misnomer (0)

Anonymous Coward | more than 5 years ago | (#28275919)

Your correct in that the hubble constant implies a limit on the observable universe from each observer (In some sense we are each the "center" of the universe)

We are however able to view distant galaxies receeding at faster than the speed of light (from our perspective!!) due to metric expansion of space itself.

Obviously at some point light from outside our verse pointing twoard our verse will never reach us because at extremely large distances space between expands faster than information can travel.

I don't think its correct that red-shifting causes objects in the observable universe to disappear. The CMB is the most distant thing we can observe and yet we can still detect it at Microwave energies.

Re:Hubble constant now a misnomer (2, Interesting)

cheftw (996831) | more than 5 years ago | (#28270311)

And how come it's measured in some stupid space unit? It's a frequency so it wants hertz!

http://www19.wolframalpha.com/input/?i=hubble+constant+in+hertz [wolframalpha.com]

It's called SI. Get with the program dudes.

Re:Hubble constant now a misnomer (1, Informative)

Anonymous Coward | more than 5 years ago | (#28270447)

And how come it's measured in some stupid space unit? It's a frequency so it wants hertz!

The Hubble constant tells you the speed that astronomic objects move away from us (or from any point in the universe, cf. Galilei invariance) depending on how far it already is, hence (km/s)/Mpc. An object at the distance of 1 Mpc moves away at approximately 74 km/s.

Now what exactly does the value in Hz tell you? Nothing.

Re:Hubble constant now a misnomer (3, Interesting)

Khashishi (775369) | more than 5 years ago | (#28270863)

The value in Hz gives you the scaling frequency of the universe. It makes sense to talk about the inverse of this frequency, which is in seconds, which is the time it takes for the universe to grow to e times its former size.

Re:Hubble constant now a misnomer (2, Insightful)

cheftw (996831) | more than 5 years ago | (#28271981)

It tells you everything. Multiply it by a distance - you get a speed. Way more useful than the other one IMHO.

Re:Hubble constant now a misnomer (1)

Daniel Dvorkin (106857) | more than 5 years ago | (#28270497)

It's measured in "stupid space units" because it's used in astronomy, of course. "Kilometers per second per megaparsec" has a much more intuitive interpretation, when considering the speed at which distant galaxies are moving away from us, than does "cycles per second."

Re:Hubble constant now a misnomer (1)

Celestial Avatar (946512) | more than 5 years ago | (#28270865)

Hubble's constant is a measure of how the expansion velocity (in units of kilometers per second) of the universe changes with an object's distance from us (in units of megaparsecs), yielding units of km/s/Mpc. It is improper to simply cancel the distance units which would leave you with units of frequency (i.e., inverse seconds).

Another example in astronomy is the unit given to monochromatic flux, which typically has units of Joules/meter^2/second/Hertz. Note that the unit has both seconds and Hertz. Now, one may naively simply cancel Hertz and seconds, leaving the unit as Joules/meter^2, but this is wrong. Monochromatic flux measures the energy (in Joules) passing through an area (in square meters) in a given time interval (in seconds) of light of a specific frequency (in Hertz). Seconds and Hertz are measuring different quantities and cannot be cancelled when dealing with monochromatic flux.

Re:Hubble constant now a misnomer (2)

cheftw (996831) | more than 5 years ago | (#28271943)

I have no wish to start an internet argument, nor is astrophysics my department, but I would bet you a shiny penny that if you did cancel them nothing bad would happen. Life would go on and all your calculations would be correct. (Assuming you got them right in the first place).

Counterexamples welcome.

Re:Hubble constant now a misnomer (1)

Betelgeuse (35904) | more than 5 years ago | (#28274275)

Is something "bad" going to happen? No. Does it make interpretation of the quantity more confusing? Absolutely.

Re:Hubble constant now a misnomer (1)

Artifakt (700173) | more than 5 years ago | (#28275207)

Think of Gauss's formula: e to the i x pi power +1 = 0.
This usually gets taught as part of second semester calculus or so. It gives some students headaches, because it emphasizes so strongly how raising a number to a power isn't really best understood as self multiplication once we get beyond the integers (It's fairly simple to see e to the 4th as e x e x e x e, but harder to imagine what e to the i or pi power involves). Just doing one of the simplest possible operations to the equation, making it read: e to the i x pi = -1, shouldn't do anything bad, should it? Some students rush to do this, after all, it makes the equation 1 term smaller.

      But the 'point' of the equation, the thing the student needs to understand so he or she sees why knowledge of e lets that student integrate and derive for a whole bunch of functions that the student couldn't deal with at all the prior semester, is that e is that number which is the base of a function that maps sums onto products, and whose rate of change is identical to itself. The actual value of e can be determined by a limit:

Lim (as delta x goes to 0) of (e to the power delta x)-1 / delta x = 1.

What's the derivitive of a constant (such as 1)? Zero! And just doing an operation most of us learned in first grade obscures the relationship and makes it harder for the student to understand.

Re:Hubble constant now a misnomer (1)

cheftw (996831) | more than 5 years ago | (#28276403)

I think you need haskell to determine e that way :)

But where would you differentiate a constant? Like 2 is a constant, but d/dx(2^x)=(ln2)(2^x)!=0

Re:Hubble constant now a misnomer (1)

selven (1556643) | more than 5 years ago | (#28270415)

Technically, the only way the Hubble constant can be a constant is if the universe is expanding exponentially.

Re:Hubble constant now a misnomer (1)

electrostatic (1185487) | more than 5 years ago | (#28271179)

Just the opposite. "Hubble Constant" generally refers to Ho, which is the current rate of expansion.

After the Big Bang, mutual gravitation of mass in the Universe slowed the rate such that expansion went at about t^(2/3) -- see http://en.wikipedia.org/wiki/Friedmann_equations [wikipedia.org] for the scale factor (rate of change of expansion) in a matter-dominated universe.

Einstein's General Relativity says that space contains energy -- called dark energy or vacuum energy, which has the effect of causing inflation. After about 10 billion years of expansion, the amount of dark energy became greater than the total amount of mass of normal and dark matter (which does not change). Now it's about 70+% of the total mass. Consequently the rate of expansion has increased to become exponential. IOW, the scale factor is now going as e^t.

In any event, the Hubble "constant" is a measure of how fast the Universe is expanding. This rate has never been constant when considered over a period of, say, a billion years. It is slowly changing. Currently -- and forever more -- the Hubble parameter is increasing due to the exponential rate of creation of new space, ie, dark energy.

Re:Hubble constant now a misnomer (1)

selven (1556643) | more than 5 years ago | (#28271931)

I was talking about the km/sec/megaparsec value. If the rate of change (speed they're flying away from us, aka derivative) is directly proportional to the current value (the distance, if this was a graph it would be the y coordinate), it's an exponential function.

Re:Hubble constant now a misnomer (1)

electrostatic (1185487) | more than 5 years ago | (#28279675)

You are correct. Currently the scale factor, a(t), goes as e^kt. The Hubble parameter can be defined defined H(t) = (da/dt)/a.

Therefore we take the derivative of e^kt and get k*e^kt. Substituting, H(t) = k * e^kt / e^kt = k.

Thus H(t) is constant in an exponentially expanding universe.

Re:Hubble constant now a misnomer (0)

Anonymous Coward | more than 5 years ago | (#28273229)

The Hubble *parameter* has never been a constant, even in the ''classical'' models. The Hubble *constant* usually means the rate of expansion as it is measured *now*. What has been discovered in 1998 is that the expansion is accelerating in stead of decelerating as they expected.

Re:Hubble constant now a misnomer (1)

Artifakt (700173) | more than 5 years ago | (#28274917)

Some of the inflationary models also suggest the universe is very, very much bigger than the part we could theoretically see, a factor of about 10e30 times or more. (We could theoretically look back close to the total age of the universe, and because of expansion, the total distance would actually be at least a bit more than 2x larger than that roughly 12 Billion years would seem to allow, say 26-30 Billion LY radius.).
        For those models where the total size of the universe is so much bigger than the observable part, theory predicts there could be many zones, each with differing Hubble constants as well as other variant properties. So even if it turns out the local expansion isn't really accelerating, 'The' Hubble constant may still be just one of many.

Re:Hubble constant now a misnomer (0)

Anonymous Coward | more than 5 years ago | (#28275733)

The expansion of the universe is expanding because the universe is expanding...

The hubble constant is kind of like compound interest - the more money you have the more in interest you get. The "interest" rate itself is a fixed constant value but the money increases over time.

Think of the distance between most gravitationally unbound galaxies as money and the hubble constant is the interest rate (Amount of new space created between galaxies)

There is more and more space so galaxies expand faster and faster but at any point in time the expansion rate given any current distance is goverened by the hubble constant.

Now there are plenty of "theories" out there that play with the hubble constant (interest rate) over time... None of which have ever predicted anything useful :)

Re:Hubble constant now a misnomer (1)

michaelwv (1371157) | more than 5 years ago | (#28277941)

The expansion rate of the Universe at the present time is called the Hubble constant. Astronomers more generally refer to the Hubble parameter to describe the expansion rate as a function of cosmic time. We have known that the Hubble parameter changes with time for at least 60 years, but, as you note, we've only known that the rate is currently accelerating for the past decade.

*Checks the Hubble Constant* (4, Funny)

Alzheimers (467217) | more than 5 years ago | (#28269865)

Yep, he's still dead.

Re:*Checks the Hubble Constant* (2, Funny)

Red Flayer (890720) | more than 5 years ago | (#28270057)

So is the value 0 or 1?

I'd assume the dead state is 0, and the live state is 1 -- except Hubble was living while he calculated the value, so he may have assigned 0 to the live state, and 1 to the dead state. Or he might have foreseen my current problem and switched the values just to trick me.

Speaking of which (my current problem), it appears my doomsday machine has entered into a positive feedback loop, and I'll only know how to fix it and save the planet if I have the correct value. I'd appreciate an accurate (and swift) answer if you can kindly help me.

Re:*Checks the Hubble Constant* (0)

Anonymous Coward | more than 5 years ago | (#28270337)

The doomsday machine output should have a value with a lower limit of 0 and an upper limit of 1. Fractional parts should be rounded to the nearest integer.

Re:*Checks the Hubble Constant* (3, Funny)

Red Flayer (890720) | more than 5 years ago | (#28270407)

The doomsday machine output should have a value with a lower limit of 0 and an upper limit of 1. Fractional parts should be rounded to the nearest integer.

Poppycock.

The outcome of my doomsday machine is DEATH. And SUFFERING. Also, some Mountain Dew. But mostly DEATH.

Re:*Checks the Hubble Constant* (1)

Hurricane78 (562437) | more than 5 years ago | (#28280175)

Our two outcomes are DEATH. And SUFFERING... And Mountain Dew..
Our three outcomes are...

On another note: What's the difference from Mountain Dew and DEATH?

Re:*Checks the Hubble Constant* (4, Funny)

Chris Burke (6130) | more than 5 years ago | (#28270523)

Yep, he's still dead.

But that measurement is only accurate to within 10%.

10% Might have mattered in the Princess Bride (0)

Anonymous Coward | more than 5 years ago | (#28271019)

Miracle Max: He probably owes you money huh? I'll ask him.
Inigo Montoya: He's dead. He can't talk.
Miracle Max: Whoo-hoo-hoo, look who knows so much. It just so happens that your friend here is only MOSTLY dead. There's a big difference between mostly dead and all dead. Mostly dead is slightly alive. With all dead, well, with all dead there's usually only one thing you can do.
Inigo Montoya: What's that?
Miracle Max: Go through his clothes and look for loose change.

Re:*Checks the Hubble Constant* (1)

Hurricane78 (562437) | more than 5 years ago | (#28280107)

'E's not dead! 'E's pinin' for the nebulas!

Volume of universe? (1)

ubergeek65536 (862868) | more than 5 years ago | (#28270033)

How can something of infinite size have a volume?

Re:Volume of universe? (0)

Anonymous Coward | more than 5 years ago | (#28270189)

I think you just answered yourself

Re:Volume of universe? (0)

Anonymous Coward | more than 5 years ago | (#28270289)

Wait, infinite volume!?!? ... and here my amp only goes up to 11!

Re:Volume of universe? (1, Insightful)

Yokaze (70883) | more than 5 years ago | (#28270233)

AFAIK, the universe is not infinite in size, it is just infinite. The very same way a circle is infinite, but has a length, or a ball or torus a surface.

Re:Volume of universe? (1)

Khashishi (775369) | more than 5 years ago | (#28270883)

That makes no sense. Thank you for playing. Maybe you mean a circle has an infinite number of points?

Re:Volume of universe? (1)

vlm (69642) | more than 5 years ago | (#28271503)

Maybe you mean a circle has an infinite number of points?

Getting closer ... infinite number of tangents at a constant radius from one central point.

Infinite number of points is just any ole line or squiggle.

Re:Volume of universe? (1)

david_thornley (598059) | more than 5 years ago | (#28272349)

Finite means limited; infinite means unlimited.

Now, take a circle. Put a pencil tip on one point and start moving it along the circumference (clockwise or counterclockwise, it doesn't matter). Now, get back to me when you've reached the end and can't go any further. You can continue infinitely far along a curve of finite length.

The ideas I've seen about an infinite but not infinitely-sized Universe tend to be more complicated, but it's the same general principle.

Re:Volume of universe? (1)

Jarjarthejedi (996957) | more than 5 years ago | (#28272123)

Who modded "a circle is infinite" as insightful? A circle with a finite radius has a finite area, only a circle with infinite radius has infinite area. As the other responses to this say a circle does have some qualities which are infinite, but that doesn't make it infinite (anymore than 1 is infinite because it belongs to the natural numbers which are infinite is a good argument).

Re:Volume of universe? (1)

Betelgeuse (35904) | more than 5 years ago | (#28274235)

I know what you're saying, but I think you're just confusing it.

The standard way to say this is that the universe is "finite but unbounded," in the same way that the [i]surface[/i] of a sphere is.

Re:Volume of universe? (1)

harryandthehenderson (1559721) | more than 5 years ago | (#28270391)

Whoever said the universe had an infinite size?

Re:Volume of universe? (1)

rm999 (775449) | more than 5 years ago | (#28270671)

The size of the Universe is entirely an unknown. As such, scientists don't talk about it much.

Re:Volume of universe? (1)

Khashishi (775369) | more than 5 years ago | (#28270963)

There are some WMAP data in which the low quadrupole moment of the CMB patterns suggests that the universe might, in fact, be finite. But it's REALLY iffy in my opinion, and other than that, there's no evidence (AFAIK) for a finite universe, despite ubiquitous claim.

Re:Volume of universe? (1)

dmartin (235398) | more than 5 years ago | (#28271511)

The size of the Universe is entirely an unknown. As such, scientists don't talk about it much.

Not entirely unknown. We have some pretty good lower bounds on what it can be =).

Re:Volume of universe? (0)

Anonymous Coward | more than 5 years ago | (#28270465)

If you've accepted that universe started in Big Bang and expanded ever since, how difficult it is to accept it expanded to a some finite point?

Re:Volume of universe? (0)

Anonymous Coward | more than 5 years ago | (#28270545)

How can something of infinite size have a volume?

The universe is finite.

Re:Volume of universe? (1)

JohnFluxx (413620) | more than 5 years ago | (#28270595)

When people talk about whether the universe is infinite or not, they are referring to the whole thing.

When people talk about the volume, they are referring to the observable universe. The observable universe is about 93 light years across

Re:Volume of universe? (2, Informative)

east coast (590680) | more than 5 years ago | (#28270691)

I think you forgot a few digits... it's about 93 billion light years across.

Re:Volume of universe? (2, Funny)

JohnFluxx (413620) | more than 5 years ago | (#28271117)

Good grief, I'm off by a factor of a billion and people complain. So picky :P

Re:Volume of universe? (1)

JustSee12 (1369599) | more than 5 years ago | (#28270767)

What are you talking about? The Milky Way alone has a diameter of around 100,000 light years.

Re:Volume of universe? (1)

Celestial Avatar (946512) | more than 5 years ago | (#28270895)

The observable universe is about 93 light years across

So you're one of those reeeally young earth creationists...

Re:Volume of universe? (1)

djp928 (516044) | more than 5 years ago | (#28270965)

It isn't infinite in size. The size is approaching infinity, though. The universe is finite, but unbounded--meaning it is finite in volume at any given time, but is constantly increasing in size as space expands.

We may never know exactly "how big" the universe really is, since we are effectively cut off from whatever is beyond the edge of the observable universe. Anything that might be beyond that is expanding "away" from us faster than light--so we can never see it from here, and can likely never go there (barring discovery of true FTL travel).

Re:Volume of universe? (0)

Anonymous Coward | more than 5 years ago | (#28277973)

>It isn't infinite in size. The size is approaching infinity, though.

Umm, that's an odd thing to say. Do you mean the size is simply getting larger? "My dog's age is approaching infinity, although it's likely to cease in a few years..."

Or do you mean that it's nearly AT infinity? If so - and if your initial (unproven) assertion is correct - then I'm afraid it's a long long way off infinite size. When every cubic nanometer of the current finite universe is represented, once for every nanosecond of its life, by a volume the current size of the universe, then we will only just have started counting! Infinity is big.

Re:Volume of universe? (1)

djp928 (516044) | more than 5 years ago | (#28295553)

I mean it in the same sense as when you're talking about limits in calculus. The size of the universe is tending towards infinity--meaning it is growing without limits.

Re:Volume of universe? (5, Informative)

JustinOpinion (1246824) | more than 5 years ago | (#28271329)

We have to be more careful with what we mean by 'size' and 'volume' and such.

The observable universe [wikipedia.org] is the region of space we can see. The universe has a finite age, so there is a finite distance over which we can see. Any further than that, and light literally hasn't had enough time to reach us. So there is indeed a boundary beyond which we cannot observe. This boundary recedes as time goes on. The universe is ~13.5 billion years old, but because the universe was expanding during all that time, the observable universe is bigger than just 13.5 billion light-years (see comoving distance [wikipedia.org] )... in fact it is 46.5 billion light-years in radius.

Now there is every indication that the universe extends beyond the cosmological horizon. So as the universe ages, we see more and more of the full universe, which is much larger than our observation volume. So how big is the universe as a whole? Our best understanding right now is based on the curvature of spacetime [wikipedia.org] . If spacetime at large scales is curved, then the universe can loop back upon itself and thus the universe is finite. If spacetime is perfectly flat on cosmological scales, then in fact the universe as a whole is infinite in size.

Our best measurements indicate the universe is flat, within error. Our best theories of the origin of the universe, coupled with available data, generically predict that the universe is infinite. So our current best answer is that the universe is infinite in size/volume. A strange result, perhaps, but that's our best understanding of the current data. Now there are indeed errors on our measurements, so our universe could be smaller. But the curvature is so small that it implies our universe contains at least [mit.edu] 1000 Hubble volumes [wikipedia.org] (the Hubble volume is the surrounding space beyond which nothing is accessible since matter is receding faster than light). Others have analyzed the night-sky looking for 'repeat patterns' that would be expected for smaller closed universes, and no such patterns have been found.

So the observable universe is finite (but ever-expanding), and the full universe is considerably larger (infinite according to our current best data and theories).

Re:Volume of universe? (1)

ubergeek65536 (862868) | more than 5 years ago | (#28272279)

Who says the universe has a finite age? The observable universe might have an age if defined in such a way as creation by some large scale event (aka big bang) What we know of the universe is just one "big bang event" out of a possible infinite number of others over an infinite amount of time. I think the problems begin when astrophysicists make the assumption that universe was created in the first place.

FYI: A maser is... (0)

Anonymous Coward | more than 5 years ago | (#28270073)

A microwave aser.

How big? (1)

T Murphy (1054674) | more than 5 years ago | (#28270097)

Once the Square Kilometer Array is completed

The name sounds impressive, but how big will it be?

Re:How big? (2, Funny)

JustOK (667959) | more than 5 years ago | (#28270517)

about 298997.51157527 square fathoms. HTH.

Re:How big? (1)

Zerth (26112) | more than 5 years ago | (#28271455)

Around pi * 318,309.886 m^2

Re:How big? (1)

meringuoid (568297) | more than 5 years ago | (#28273237)

The name sounds impressive, but how big will it be?

One square kilometre to begin with, although the rate at which it will be expanding is yet to be measured to sufficient accuracy.

Award for finding the Hubble Constant (0)

Anonymous Coward | more than 5 years ago | (#28270153)

Great Experimental Idea (4, Informative)

Colonel Korn (1258968) | more than 5 years ago | (#28270271)

1 - Distance measurements are currently kludged together very carefully using bridging. We use one measurement, for instance parallax based on the Earth's movement over 6 months, to show us the distance to a star that has some particular properties and which our models say should always be a certain luminosity. The parallax measurement has error bars.

2- Then we find a much more distant star of that same type that is near a particular type of supernova, and measure its brightness, comparing that to the brightness of our first star to give the distance to the distant star, and thus the supernova as well. That has bigger error bars.

3- Then we look for that type of supernova in very very distant galaxies. Supernovae are brighter than the rest of their galaxy put together while they're burning hot, so we can see them at tremendous distances. We use the measured brightness of that supernova to determine the distance to its galaxy.

4- Then we pair the knowledge of its distance with its velocity with respect to us, which we can determine through redshifting of something with a familiar spectrum. More error bars. That becomes a single point for the determination of the Hubble Constant (and yes, the "constant" is changing).

With only a cursory glance at TFA, it looks to me like this is a way to skip to step 3 or 4, thereby avoiding the need to bridge these length-scales using several techniques.

Re:Great Experimental Idea (1)

anarchyboy (720565) | more than 5 years ago | (#28270635)

Yes it looks like they are measuring the distance by paralax using the fact that galaxies are in fact quite wide really. From the article it looks like this has been done before for galaxies close by which is not very usefull for measuing hubbles constant but that they have found way of amplifying the signal from distant galaxies. What the article doesn't say is how they measure both the linear and angular size of the gallaxy which is required to gauge the distance it just says that they did. If so then this is indeed very good news for narrowing down hubbles so called constant.

As a side note using standard candles is as you said very hard and requires bridging as you put it, one method used is I believe to assume that distant galaxies have a maximum size / brightness which puts a bound on the distance to them. The measurement of velocity is actually very acurate and easy and while it may contribute to the error bars of the estimate in hubbles constant I think the contribution would be tiny compared to the problems in measuring distance.

Re:Great Experimental Idea (1)

Betelgeuse (35904) | more than 5 years ago | (#28274265)

The trouble is that these galaxies aren't that far away (despite the article summary says). They're quite a bit further away than the previous measurements of water masers, but you still need to use Type Ia supernovae to actually get to the distances where this discussion gets interesting. The cool thing about the water masers is that they might allow us to get out a bit further without using another "rung" on the distance ladder, but there is no way that they are going to replace the (much, much more distant) Type Ia supernovae.

Um, no. Hubble's assistant says its not a constant (0, Troll)

UnknownSoldier (67820) | more than 5 years ago | (#28270283)

Halton C. Arp, a professional astronomer was Edwin Hubble's assistant, says otherwise ...

http://www.electric-cosmos.org/arp.htm [electric-cosmos.org]

Electric Universe? (1)

Chris Daniel (807289) | more than 5 years ago | (#28270639)

Maybe you should present a more credible source, if you wish to be taken seriously.

Re:Electric Universe? (1)

UnknownSoldier (67820) | more than 5 years ago | (#28271097)

Edwin Hubble's assistant isn't credible enough?!

lol !

--

William A. Tiller, Materials Sciences Department, Stanford University wrote: "The present scientific establishment has grown somewhat fossilized by its current world picture and is locked into a view of reality that has outlived its usefulness. It has begun to limit mankind's growth and has so increased its sense of specialization, separateness, materiality, and mechanical computer-like functioning that it is in real danger of self-extermination."

Re:Electric Universe? (0)

Anonymous Coward | more than 5 years ago | (#28271759)

Just a hint, science is not about who you are, it is (at least stated simplistically) about what you can say and defend with evidence. Asserting that someone is credible because they were Edwin Hubble's assistant is a logical fallacy known as an appeal to authority. The only credibility that should ever be recognized in science is that which comes from theory, built from testable hypotheses, and supported by all available evidence. Anything else is, quite frankly, madness.

Re:Electric Universe? (1)

Chris Daniel (807289) | more than 5 years ago | (#28272231)

The website is what I was questioning, really, although another reply hits on the fact that simply being an assistant to Hubble does not necessarily make a person credible. electric-cosmos.org is a proponent of the "electric universe" "theory" -- which has been thoroughly rejected over and over, but remains a favourite of the conspiracy theorist type.

Re:Electric Universe? (1)

UnknownSoldier (67820) | more than 5 years ago | (#28331625)

> electric-cosmos.org is a proponent of the "electric universe" "theory" -- which has been thoroughly rejected over and over

NASA begs to differ... [elsevier.com]

The TSS-1R electrodynamic tether experiment: Scientific and technological results

N. H. Stonea, W. J. Raittb and K. H. Wright, Jr. c
a Space Sciences Laboratory, NASA Marshall Space Flight Center, Huntsville, AL 35812, USA
b Center for Atmospheric and Space Science, Utah State University, Logan, UT 84322, USA
c Center for Space Plasma and Aeronomic Research, University of Alabama in Huntsville, AL 35899, USA

Available online 25 July 2003.

Abstract

The Tethered Satellite System program was designed to provide the opportunity to explore certain space plasma-electrodynamic processes (associated with high-voltage bodies and electrical currents in space) and the orbital mechanics of a gravity-gradient stabilized system of two satellites linked by a long conducting tether. A unique data set was obtained during the TSS-1R mission in which the tether electromotive force and current reached values in excess of 3500 volts and 1 amp, respectively. The insight this has allowed into the current collection process and the physics of high-voltage plasma sheaths is significant. Previous theoretical models of current collection were electrostatic--assuming that the orbital motion of the system, which is highly subsonic with respect to electron thermal motion, was unimportant. This may still be acceptable for the case of relatively slow-moving sounding rockets. However, the TSS-1R results show that motion relative to the plasma does affect current collection and must be accounted for in orbiting systems.

But I guess its easier to believe in scientific dogma, then keep an open mind.

Re:Electric Universe? (1)

Chris Daniel (807289) | more than 5 years ago | (#28359013)

I am disappointed that this was the best you could come up with to support your theory. The existence of cosmic plasmas such as those encountered by the TSS-1R mission is quite widely accepted. Proving that they have the effects claimed by the theory you apparently advocate is quite another matter.

I read the first chapter of the book on electric-cosmos.org, and it mostly seems to be jeering at the complexity and unintuitive nature of current theories, while also heavily emphasizing the "unprovability" of any type of astrophysical theory. How convenient. Perhaps it's a bit tough on the underdog supporters, but when it comes to scientific inquiry, the burden of proof is very much upon the challenging theory. So far, the "electric universe" crowd has produced absolutely nothing compelling, other than cries of "help help, I'm being repressed!"

It's easier for me to believe the majority of scientists ("scientific dogma" if you prefer) than an ostracized minority. There is a large difference between keeping an open mind and pouring my uneducated (I'm not an astrophysicist) efforts into supporting a currently unacceptable theory.

Good enough? (1)

dandart (1274360) | more than 5 years ago | (#28270363)

Presumably "Erm, around 100" isn't good enough then?

Good Enough? (1)

Kozar_The_Malignant (738483) | more than 5 years ago | (#28270579)

When I was doing university physics with a slide rule, three significant figures ( 74.2 ± 3.6 (km/s)/Mpc) was good enough for anything. Is our next probe going to miss M31? Oh yeah, get off my lawn too. :-)

Re:Good Enough? (2, Informative)

John Hasler (414242) | more than 5 years ago | (#28271023)

> When I was doing university physics with a slide rule, three significant figures ( 74.2
> ± 3.6 (km/s)/Mpc) was good enough for anything.

When I was doing university chemistry with a book of log tables four significant figures was barely good enough for my homework.

Re:Good Enough? (1)

Prof.Phreak (584152) | more than 5 years ago | (#28271681)

Indeed. This constant may not be a constant. It may not be the same everywhere in the universe. So by observing things very far away (distance and time), we may actually end up with a less accurate number for a `local' variable.

Bad Labrador (2, Interesting)

Bad Labrador (922836) | more than 5 years ago | (#28271047)

I've been following Alexander F Mayers work on Minkowski's (Einsteins Maths Teacher) space time mathematics which Einstein, who didn't understand them, called "superfluous erudition'. Mayer derives a model for the universe that does not require the universe to be expanding, let alone accelerating expansion, does not require "Dark matter" nor "Dark energy", that makes a damn sight more cosmological sense than the "Big Bang" and fits the current observations, much, much better, with no free variables like "quintessence". He makes a prediction for the LRO mission as well. http://www.jaypritzker.org/index.html [jaypritzker.org]

Re:Bad Labrador (1)

anarchyboy (720565) | more than 5 years ago | (#28271865)

Well since Minkowski latter came to be a major contributor to the development of the theory of relativity he clearly decided that they weren't worth the effort either. Any model the does not require the universe to be expanding must really take some work to avoid the fact that it clearly is. The fact the dark matter has nothing to do with the universe's expansion well that is to say the evidence for dark matter does not rely on it. Proposing that dark matter does not exist would require rethinking not just relativity but newtons gravitational laws. Also what makes more sense than the big bang? I assume since it makes more sense you could explain it for me?

Re:Bad Labrador (1)

Bad Labrador (922836) | more than 5 years ago | (#28272363)

The only evidence for expansion is that the further away a galaxy is from us, the more red shifted it is. Mayer/Minkowskis equations show that the red shift may be an artifact of curved space time and not a radial recessionary velocity at all. His equations appear to fit the observed data much better and explain such things as the Pioneer anomaly much better. If Mayer is correct, the Hubble constant measurements are merely measuring the change of timelines due to the curvature of spacetime. Needless to say, Mayer is not a popular man.

Re:Bad Labrador (2, Insightful)

anarchyboy (720565) | more than 5 years ago | (#28272777)

Why not? If he's theory is right surely that would be a good thing? interestingly I read the book you linked to and found it quite hard going, there was little explanation of the ideas presented and seemed to have many descriptive quotes from people like minkowski that were then interpruted, woryingly these 'sound bites' were offered as support of the theory presented.

The multi-dimensional description of time was woefully under explained, probably due to a lack of a concise mathematical description but was instead given a more general description. As a physicist I have a precise understanding of what the space time of general relativity is mathematicaly the physical interperation can be tricky at times and the mathematics hard but it is very well defined and unfortunatly the link you gave did not furnish me with the similar well defined mathematical description of the Mayer's theory.

I would be interested to see a derivation of some known results from GR or newtonian gravity and from cosmology, reproduced in Mayer's frame work as this would provide a good starting point from which to understand the theory. Just in case you are interested I would like to see how the theory reproduces orbital trajectories (ie keplers laws), The equivalent description of the CMB would also be usefull. I may just me being lazy but as you've probably guessed I'm not overly impressed so far.

What really ticked the 'crackpot' box for me though was the single publication, proclaimed as a revolution of great importance. I would like to include a quote but it appears i can't copy and paste it so just read the last paragraph on page 136. Such a statement really has no place in a scientific document and is really indicative of the entire document

hubble ? (-1, Troll)

Anonymous Coward | more than 5 years ago | (#28271147)

why do they call it hubble ? seriously was it funded by scientology ?

To get it over with... (-1, Troll)

Anonymous Coward | more than 5 years ago | (#28271283)

now all we need are tiarks with frickin' mazer beams on their heads.

Within 10%??? (0)

Anonymous Coward | more than 5 years ago | (#28271439)

I just don't understand this.

FTA:
1) The current best value for the Hubble Constant is 74.2 ± 3.6 (km/s)/Mpc
2) Most astronomers agree that that's within 10% of its actual value

But shouldn't everyone, even astronomers, agree that value is within 5% of 74.2?
If the actual value is, say 80, then why say ± 3.6?

cave man measure hubble constant (0)

Anonymous Coward | more than 5 years ago | (#28271565)

cave man measure it good

So their measurement of the Hubble constant is 69 (1)

boot_img (610085) | more than 5 years ago | (#28271817)

According to the article "the astronomers determined that the galaxy UGC 3789 is 160 million light-years from Earth". This translates to 49 Mpc. According to NED [caltech.edu] , the velocity (in the Cosmic Microwave Background frame) is 3385 km/s.

Therefore this measurement of the Hubble parameter is then 3385/49 = 69 km/s/Mpc.

(Unfortunately the article does not quote an uncertainty on the 49 Mpc measurement. Because of peculiar velocities, I would estimate that there is at least a 300 km/s uncertainty on the 3385 km/s velocity. )

Re:So their measurement of the Hubble constant is (1)

Betelgeuse (35904) | more than 5 years ago | (#28274893)

It's also possible that this galaxy is not totally in the Hubble Flow. In other words, it might be pulled around by other nearby galaxies/galaxy clusters. All galaxies are affected by this to some extent, but with nearby galaxies (like this one), these gravitationally-caused velocities can be significant compared to the Hubble expansion-caused velocities.

Anonymous Coward (0)

Anonymous Coward | more than 5 years ago | (#28272307)

The actual value is 42 nmi/sec/MPC. It would be in nautical miles because the Earth was designed to calculate the answer.

10%? I should hope so (1)

jandersen (462034) | more than 5 years ago | (#28277077)

The current best value for the Hubble Constant is 74.2 ± 3.6 (km/s)/Mpc according to recent conventional methods and the recently restored Hubble Telescope. Most astronomers agree that that's within 10% of its actual value.

10% of 74 is 7.4, corresponding to ± 3.7; meaning that in the very worst case, where the true value is at one end of the interval, we can only get about 10% away. What the astronomers agree on is that the estimate of the uncertainty on the measurements is something like ± 3.6. This is not as trivial a matter as it would seem - it can be quite complex to calculate and is a source of many of the more embarrasing errors in science.

ahh thats not exactly right (0)

Anonymous Coward | more than 5 years ago | (#28277239)

This thread is now about,
Alexander F. Mayer [jaypritzker.org] .

The Perimeter Institute recently gave a lecture... (1)

NoseyNick (19946) | more than 5 years ago | (#28325781)

The Perimeter Institute recently gave a lecture on this, by Brian Schmidt, Australian National University - "The Universe From Beginning to End". I understand they will EVENTUALLY make these lectures available on their website, after they've made a bit of money by showing them on Discovery etc: https://www.perimeterinstitute.ca/en/Outreach/Public_Lectures/Public_Lectures/ [perimeterinstitute.ca]
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