UKC

/ The Universe is expanding faster than thought

This topic has been archived, and won't accept reply postings.
what the hex on 11 May 2018
wercat on 11 May 2018
In reply to what the hex:

or our dimensions are shrinking ?

To be Frank on 11 May 2018
In reply to wercat:

Here's a weird thought, what if the other 6 or 7 curled up dimensions started expanding?

1
GrahamD - on 11 May 2018
In reply to what the hex:

Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. 

what the hex on 11 May 2018
In reply to Lusk:

Now we have two different measurements for the Hubble constant, does that prove that the Universe is expanding in a non uniform way?

Has the Cosmos gone Pear Shaped?

what the hex on 11 May 2018
In reply to GrahamD:

Aha! Douglas Adams!

wercat on 11 May 2018
In reply to Lusk:

perhaps entanglement will stop working, for all we know "spooky action at a distance" may be no distance at all through the everywhere present tiny dimensions and therefore permissively instantaneous.

1
what the hex on 11 May 2018
In reply to wercat:

my brain is entangled!

what the hex on 11 May 2018
In reply to what the hex:

> Aha! Douglas Adams!

He died 17 years ago today!

GrahamD - on 11 May 2018
In reply to what the hex:

> He died 17 years ago today!

That long ago.  Wow.

GrahamD - on 11 May 2018
In reply to what the hex:

To be fair, we didn't really know why it was what we thought it was previously.  It was only a few months ago there was a study saying the Cosmological constant could actually be smaller than first thought.  Truth is new discoveries are happening so quickly its hard to keep up.

DancingOnRock - on 11 May 2018
In reply to what the hex:

Space is probably expanding non uniformly in a chaotic manner. Just like most other things within it. 

 

GrahamD - on 11 May 2018
In reply to DancingOnRock:

> Space is probably expanding non uniformly in a chaotic manner. Just like most other things within it. 

Based on what ? that isn't what most observations show - that space is very (but not completely) uniform wherever we look.

wercat on 11 May 2018
In reply to GrahamD:

> Based on what ?

The wave harmonic theory of historical perception, in its simplest form, states that history is an illusion caused by the passage of time, and that time is an illusion caused by the passage of history. It also states that one’s perception of these illusions is conditioned by three important factors: who you are; where you are; and when you last had lunch with Zaphod Beeblebrox.

 

tripehound - on 11 May 2018
In reply to Lusk:

> Here's a weird thought, what if the other 6 or 7 curled up dimensions started expanding?

Please don't do that.

pasbury on 11 May 2018
In reply to GrahamD:

I need a towel.

Hooo - on 12 May 2018
In reply to what the hex:

I swear the walk to the station gets a little longer every day.

FactorXXX - on 12 May 2018
In reply to GrahamD:

> Based on what ? that isn't what most observations show - that space is very (but not completely) uniform wherever we look.

Are those observations based on the 'Don't Panic' theory?

DancingOnRock - on 12 May 2018
In reply to GrahamD:

The surface of the sea is flat when you look at it from a long way away. 

The moon is round when you look at it from a long way away. 

When you take a snapshot of an object that is moving very fast, it appears to be stationary. You can’t know an object’s velocity and position at the same time.

Post edited at 06:58
wintertree - on 12 May 2018
In reply to what the hex:

Don’t worry, soon cosmologists will claim to have “detected” dark energynesis, a hotherto unknown source of continual dark energy production.  Bung another term in the equation.

Also, shame on the guardian for quoting the Hubble Constant as “73”.  73 what?  Bananas?   Units please.

wintertree - on 12 May 2018
In reply to DancingOnRock:

> When you take a snapshot of an object that is moving very fast, it appears to be stationary. You can’t know an object’s velocity and position at the same time.

Totally wrong from an astronomical perspective.  An awful lot of observation astronomy is about making precise measurements of an objects velocity and position from a single, still frame that is a snapshot in time.  Generally position is already well known in advance, but there’s no fundamental reason - just limits of current instruments - why that is so.

Parislly ionised elements in the surface layers of stars emit spectral lines with standard wavelengths.  These are Doppler shifted by the relative motion between those objects and us, changing their apparent colour.  This allows the measurement of their velocity in one dimension (towards or away from us - the critical dimension for expansion of the universe) in an instant.

wintertree - on 12 May 2018
In reply to GrahamD:

> Based on what ? that isn't what most observations show - that space is very (but not completely) uniform wherever we look.

I would go for a very uniform expansion.  

Attractive-gravity-matter clumps through positive feedback mechanisms - a small density increase in a uniform density cloud of particles locally increases density, attracting more.

Repulsive-gravity-matter (aka exotic matter in wormhole and warp propulsion studies aka dark energy in cosmology) is not subject to the same positive feedback mechanism that produces locally clumpy stuff.  I believe density fluctuations are naturally ironed out instead.  I have not the wit to do a Taylor series expansion in my head this early in the morning without pen and paper mind you.

wercat on 12 May 2018
In reply to DancingOnRock:

try telling that to the man with the speedgun.  Isn't there a physics joke about Heisenberg losing his knowledge of where he is when a cop tells him his exact speed?

wercat on 12 May 2018
In reply to wintertree:

>  Generally position is already well known in advance

Shouldn't that really be "position in the possibly distant past is known well in advance" for anything outside our solar system?

Post edited at 08:52
wintertree - on 12 May 2018
In reply to wercat:

> >  Generally position is already well known in advance

> Shouldn't that really be "position in the possibly distant past is known well in advance" for anything outside our solar system?

Entirely correct - the further away we look in distance and redshift, the further back in time it was when the light we now see left it.

what the hex on 12 May 2018
In reply to wintertree:

Interesting, thanks, I think I get redshift. Has a distant object ever been recorded starting to dim or even disappearing entirely as it accelerates away beyond the speed of light?

I know that faster than light travel is impossible but I read somewhere yesterday that this doesn't apply to the expansion of space. Is this right?

No Hitchhiker's puns please

To be Frank on 12 May 2018
what the hex on 12 May 2018
In reply to Lusk:

That's blown my mind, ta. There's a lot of if's and or's in that second link, I give up trying to understand and am just be amazed. Fair play to the scientists for attempting to unravel the mystery.

DancingOnRock - on 12 May 2018
In reply to wintertree:

But all those calculations are thrown into doubt if space isn’t expanding at a constant rate. What if it’s expanding in pulses or waves. What does the effect of gravity waves have on the expansion of space?

 

DancingOnRock - on 12 May 2018
Ian65 - on 12 May 2018
In reply to GrahamD:

Yes, but it's  along way to the chip shop.

GrahamD - on 12 May 2018
In reply to what the hex:

> Interesting, thanks, I think I get redshift. Has a distant object ever been recorded starting to dim or even disappearing entirely as it accelerates away beyond the speed of light?

The answer is yes and eventually if the current acceleration continues the whole observable universe will dissapear.

The objects themselves aren't moving faster than light.  Space is getting bigger faster than light.

timjones - on 12 May 2018
In reply to what the hex:

"Faster than we thought"?

 

WTH thinks about how fast the universe is expanding, haven't they got something more useful to do ;)

Post edited at 14:37
To be Frank on 12 May 2018
In reply to timjones:

When I want to fry my brains, I'd rather fry them thinking about things cosmic/quantum/stringy etc. than anything, of any variety, political.  See UKC for starters.

And it's interesting!

To be Frank on 12 May 2018
In reply to Ian65:

> Yes, but it's  along way to the chip shop.


In a parallel universe Elvis will be there.

wercat on 12 May 2018
In reply to what the hex:

the radiation from the big bang shifted so far down (partly because of the expansion of space) that the people who confirmed the earlier theorists actually detected what was already invisible to our eyes but detectable as microwave radiation.  This manifested itself as omnidirectional noise in the microwave region, at first inexplicable, investigated in a microwave horn antenna.

 

I heartily recommend Marcus Chown "The Afterglow of Creation" which tells the story in such logical completeness and in lecture style that by the time the signature of the Big Bang is detected you will have quite possibly learned and understood quite a bit about it.

wercat on 12 May 2018
In reply to Lusk:

And in another it will be Elvina

what the hex on 12 May 2018
In reply to DancingOnRock:

Ta, that looks interesting, will watch it later when I can concentrate properly.

what the hex on 12 May 2018
In reply to timjones:

Believe it or not I do have a job! Thinking about the "big questions" (like what's going on up in space and what to put on your chips) puts the pressures of life into perspective.

We're only here once! Allegedly.

timjones - on 12 May 2018
In reply to Lusk:

Thinking about politics wouldn't exactly be the first thing on my list of more useful things to do ;)

wintertree - on 12 May 2018
In reply to timjones:

> WTH thinks about how fast the universe is expanding, haven't they got something more useful to do ;)

To me it’s one of the most important question being asked at the moment.  

If we can prove that dark energy exists, and we can then learn enough to be able to create it, there is a chance that warpfield propulsion could be realised, and that people could travel to other stars really very quickly.  

 

2
Chris Murray - on 12 May 2018
In reply to what the hex:

How fast does thought expand???

wintertree - on 12 May 2018
In reply to what the hex:

> Has a distant object ever been recorded starting to dim or even disappearing entirely as it accelerates away beyond the speed of light?

This happens so slowly, and we have data going back such a short period of time, that I think it’s never been observed “in the act”.

As another poster says so well, things like the cosmic microwave background are images from a past time red shifted well down the frequency spectrum - but there were no stars back then so we won’t see those disappear.  I suspect that most of the objects we see in the sky will die from fuel exhaustion long before they red shift out of viability - but don’t quote me on that!  

I’m a bit hazy on how something disappears as it crosses the event horizon of our visible universe - I think we will see it ever more red shifted; I’m not clear what happens when it’s wavelength exceeds that of our visible universe as then we will be in the EM near field - although it’ll be so low energy we won’t know it’s there.

 

timjones - on 12 May 2018
In reply to wintertree:

I guess that depends on how you rate the importance of travelling to other stars really quickly ;)

Pero - on 12 May 2018
In reply to wintertree:

> If we can prove that dark energy exists, and we can then learn enough to be able to create it, there is a chance that warpfield propulsion could be realised, and that people could travel to other stars really very quickly.  

That's pure science fiction.  The same could be said about dilithium crystals!

 

 

Pero - on 12 May 2018
In reply to DancingOnRock:

> You can’t know an object’s velocity and position at the same time.

How do airline navigation systems work then?  You can know the position and velocity of any macroscopic object simultaneously.

 

Post edited at 21:22
Pero - on 12 May 2018
In reply to what the hex:

> I know that faster than light travel is impossible but I read somewhere yesterday that this doesn't apply to the expansion of space. Is this right?

The expansion of space isn't a speed.  Simply put, the distance between any two points in space increases over time, in proportion to the distance between them. If two objects are far enough apart, then this results in a "recessional" velocity between them that can exceed the speed of light.

The limitation of the speed of light applies to motion through space.

https://en.wikipedia.org/wiki/Accelerating_expansion_of_the_universe

Post edited at 21:38
becauseitsthere - on 12 May 2018
In reply to Ian65:

> Yes, but it's  along way to the chip shop.

and when I came out there was Gordon standing at the bus stop. 

wintertree - on 12 May 2018
In reply to Pero:

> That's pure science fiction. 

Odd - I see I have two dislikes for my post.  As a rule I don’t comment on dislikes but it’s sad to see them here.

Given our current understanding, the main thing making warp stuff pure science fiction is not knowing if dark energy is real, or knowing how to make it.  Go and google the Alcubierre metric.

> The same could be said about dilithium crystals!

Not at all, that’s purely fictional mumbo jumbo.

 

Post edited at 22:10
1
wintertree - on 12 May 2018
In reply to timjones:

> I guess that depends on how you rate the importance of travelling to other stars really quickly ;)

Well seeing as our sun is one day going to expand and sear all life, air and water off our planet, it seems quite important.

wintertree - on 12 May 2018
In reply to Pero:

> How do airline navigation systems work then?  You can know the position and velocity of any macroscopic object simultaneously.

Civilian radio multilateration navigation systems only meausre position.  They calculate velocity by measuring the time derivative of position, so in an instant they do not know velocity.

The use of Doppler shift measurements to give an instantaneous measure of velocity is possible, but is more complex and is not necessary for most applications.  

wintertree - on 12 May 2018
In reply to what the hex:

It’s also worth pointing out that as well as omitting units, the guardian article didn’t quote uncertainties.

A quick look at a plot of measurements and their uncertainties [1] shows it’s really no surprise that the latest measurement doesn’t agree with a whole bunch of previous measurements and simulations.

My interpretation is that (a) some measurements are underestimating their uncertainties and (b) the data very weakly supports a case for the Hubble constant being smaller in the past, but this is exceedingly dodgy ground until different measurements of similar redshift brackets can all agree within their uncertainties.

[1] https://en.wikipedia.org/wiki/File:Hubbleconstants.svg 

Post edited at 00:08
Michael Hood - on 12 May 2018
In reply to wintertree:

> Also, shame on the guardian for quoting the Hubble Constant as “73”.  73 what?  Bananas?   Units please.

Read the whole article

wintertree - on 13 May 2018
In reply to Michael Hood:

> Read the whole article

I did - but stating several paragraphs after it’s first used what a number “translates to” is no excuse for not putting the units in every time it is used.  Pedantic I know, but important.  To pedants like me anyhow.

I do have some sympathy for the journalist - the communities insistence on use of non SI units means there’s so simple abbreviation for the units, and in SI it’s only reasonable in exponent notation which is a bit much for a popular press article.

 

Michael Hood - on 13 May 2018
In reply to wintertree: I partly agree, like abbreviations they should be detailed on first usage.

 

Pero - on 13 May 2018
In reply to wintertree:

> Given our current understanding, the main thing making warp stuff pure science fiction is not knowing if dark energy is real, or knowing how to make it.  Go and google the Alcubierre metric.

I don't need to google the Alcubierre metric.  It's pure speculation.  It works not using dark energy but requires exotic matter with a negative energy density - which is pure speculation.

Dark energy is simply the energy density of the vacuum - there's no problem making that!

Post edited at 07:13
Pero - on 13 May 2018
In reply to wintertree:

> Civilian radio multilateration navigation systems only meausre position.  They calculate velocity by measuring the time derivative of position, so in an instant they do not know velocity.

Umm - the time derivative of position is velocity!

You could, I guess, try to avoid a speeding fine by claiming that speed cameras can only measure the position of your car and not its speed.  And hope that a scientifically illiterate magistrate might be fooled!

Post edited at 07:31
wintertree - on 13 May 2018
In reply to Pero:

>it works not using dark energy but requires exotic matter with a negative energy density - which is pure speculation.

Darg energy is excotic matter.  Both are something that have a negative energy density, thus having opposite gravitational effects to normal matter.  Exact same thing, different names.  We might need more (higher density) of it for useful warp effect under the Alcubierre metric, and perhaps we can only have the density naturally present within the quantum vacuum, but we just don’t know - we don’t even know what the negative energy density of the quantum vacuum is - and therefore can’t say that it is this that is actually driving the expansion of the universe.

> Dark energy is simply the energy density of the vacuum - there's no problem making that!

You say that but there’s been no luck reconciling theories of the quantum vacuum with observations of vacuum energy density.  

It isn’t case that they disagree a little but, but by a ratio with a lot of zeroes on the end.  It’s clear we just don’t understand it - and there’s a credible possibility that once we do, all sorts of things could be realised.  Of course this is speculation.  

That’s why the expansion of the universe is such an interesting question to me - it provides data at an area of unresolved physics, driving theory forwards, that could change so much once we understand it.

Post edited at 07:49
wintertree - on 13 May 2018
In reply to Pero:

> Umm - the time derivative of position is velocity!

Yes, I know.  Re-read the discussuon.  It was about If you can know velocity from a momentary snapshot in time.  Your example of a navigation system can not - as you need position data from two different moments in time to measure the derivative.

>  You could, I guess, try to avoid a speeding fine by claiming that speed cameras can only measure the position of your car and not its speed.  And hope that a scientifically illiterate magistrate might be fooled!

You may have noted that both myself and another poster mention the Dopoler shift above.  This measures one component of an objects velocity vector from an instantaneous snapshot.  This is what we were discussing.  Can we measure the velocity of something whose apparent motion is so slow that we effectively live in an instant, and can’t see its position change?  

Post edited at 07:43
Pero - on 13 May 2018
In reply to wintertree:

> Darg energy is excotic matter.  Both are something that have a negative energy density, this having opposite gravitational effects to normal matter.  Exact same thing, different names.

That's quite a common misconception, apparently.  There's no connection between the known/calculated positive energy density of the vacuum which causes expansion to continue in our increasingly vacuum dominated universe; and the hypothetical matter with a negative energy density, for which there is no observational evidence.

To quote from General Relativity by James Hartle, Chapter 18 on Cosmological Models:

"There is no fundamental theory that fixes the value of the vacuum energy.  We restrict our attention to a vacuum energy that is (i) constant in space and time and (ii) positive as indicated by present observations."

Hartle's book is a serious advanced undergraduate text on General Relativity, and is therefore free of pop-science misconceptions.

wintertree - on 13 May 2018
In reply to Pero:

> That's quite a common misconception, apparently. 

You’ll see I said “apparent” not “actual”.  

A theory of the vacuum energy is one of the great unsolved challenges in physics, and it’s solution hints at an awful lot.  

> There's no connection between the known/calculated positive energy density of the vacuum which causes expansion to continue in our increasingly vacuum dominated universe; and the hypothetical matter with a negative energy density, for which there is no observational evidence.

Well, that depends on how large the vacuum energy is - the larger it is the more headroom there is to produce a volume of space with less energy than the vacuum.

Post edited at 08:01
Pero - on 13 May 2018
In reply to wintertree:

Actually, while I've got Hartle open, here's an interesting point.

There's another misconception that if the vacuum energy were 0 then the universe would collapse under gravitational attraction.  But, that is not the case.  The expansion of the universe is about the evolution of spacetime itself, as governed by the Einstein Field Equations, and not about the motion of objects through space. 

In particular, a matter-dominated universe with a vacuum energy of zero could still expand forever.  But, the expansion would slow down over time.  Which is what was expected.  When observations showed an accelerated expansion, then the only solution was that the vacuum has a positive energy density that gradually dominates as the universe expands.

So, it's another over simplification of popular-science to describe the universe as dark energy trying to expand it and gravity trying to recollapse it.  If you study the mathematics of the Einstein Field Equations, you would see that this is not the case.  Even without dark energy, the universe could expand forever, if the matter density is below a critical value.

 

Post edited at 08:16
wintertree - on 13 May 2018
In reply to Pero:

> So, it's another over simplification of popular-science to describe the universe as dark energy trying to expand it and gravity trying to recollapse it.  Even without dark energy, the universe could expand forever.

Indeed; an ever expanding universe with a slowing rate of expansion was a standard solution space before dark energy came on to the scene.  Heat death or a big collapse? 

There just weren’t many TV programs about it.  

Dark matter and then dark energy generate a lot more popular science (hello Horizon) that other - far more interesting/accessible stuff.  I’ve long felt this is driven by the relevant scientific community as part of their funding PR machine...  What’s been learnt about the range and abilities of machinery within a single cell would make a phenomenal popular science TV series, but the BBC will just go and make another incomprehensible with pretty movies dark energy program...

Post edited at 08:22
wercat on 13 May 2018
timjones - on 13 May 2018
In reply to wintertree:

Why do you rate it as important?

Isn't the old saying that first you sell the problem and then you sell the answer?

 

Maybe we have too many people with a vested interest in pushing a big problem so that they can earn a living chasing expensive answers?

 

We're all going to die one day.

Robert Durran - on 13 May 2018
In reply to timjones:

> Why do you rate it as important?

> We're all going to die one day.

Yes, so in that sense nothing is important. So we might as well ask and try to answer interesting questions in the meantime - just for fun and curiosity. And few things could be as fascinating as the origin, evolution and fate of the universe.

timjones - on 13 May 2018
In reply to Robert Durran:

> Yes, so in that sense nothing is important. So we might as well ask and try to answer interesting questions in the meantime - just for fun and curiosity. And few things could be as fascinating as the origin, evolution and fate of the universe.

The questions are interesting but doesn't the constant string of incorrect answers get tiresome after a while ;)

1
what the hex on 13 May 2018
In reply to DancingOnRock:

Ho Ho, very droll

Took me until 2:54 to realise you were pulling my leg

Gordon Stainforth - on 13 May 2018
In reply to Robert Durran:

> Yes, so in that sense nothing is important. So we might as well ask and try to answer interesting questions in the meantime - just for fun and curiosity. And few things could be as fascinating as the origin, evolution and fate of the universe.

But some questions make more sense/ are more meaningful than others. A lot of these cosmological ones are right on the edge of speculation.

BTW, where's Coel when we most need him?

DancingOnRock - on 14 May 2018
In reply to what the hex:

That may not have been the right video. I didn’t re-watch it before posting as it was 6mins long. 

Essentially as it’s the speed of propagation within the universe then nothing inside the universe is going to travel faster. Anything outside the universe will have a different speed of propagation. Could be higher or lower. It doesn’t really matter unless you can find a way to step outside the universe. 

wercat on 14 May 2018
In reply to Gordon Stainforth:

> But some questions make more sense/ are more meaningful than others. A lot of these cosmological ones are right on the edge of speculation.

The sense in asking any question is relative to the mind of the questioner and as we exhibit at least the illusion of free will then we are free to set that parameter as individuals and no special position of mind is to be preferred, unless it harms others.  Wercat's principle of relativity

Robert Durran - on 14 May 2018
In reply to Gordon Stainforth:

> But some questions make more sense/ are more meaningful than others. A lot of these cosmological ones are right on the edge of speculation.

Yes, and that's why measuring the rate of expansion is so important - it allows us to ask the right questions such as what the nature of dark energy is and to rule out some of the speculation. I find it amazing what we already know from the big bang to accelerating expansion.

 

what the hex on 14 May 2018
In reply to Gordon Stainforth:

> But some questions make more sense/ are more meaningful than others. A lot of these cosmological ones are right on the edge of speculation.

What did you make of the end of 2001 then Gordon?

 

cb294 - on 14 May 2018
In reply to Lusk:

Nice! 

http://scaleofuniverse.com  gives you a scrollable version where you can zoom in or out from our scale, all the way from the Planck length to the observable universe.

The most surprising "object" for me was the size of the minecraft world, who knew that computer storage has become THAT cheap!

CB

 


This topic has been archived, and won't accept reply postings.