成人快手

Jonathan Amos.

"The existence of dark energy was established in 1998 and is one of the great discoveries of recent years.."

no. postulated (in desparation :-)) NOT established.

Your reference to dark energy indicates that it was postulated to explain an increase in the expansion rate of the universe. No reference to his observation was given.

Four dimensional space is wrongly supposed to have three dimensions of space and one of time.
Distance in the fourth dimension is given by the speed of light times the duration between two events.
The fourth dimension is therefor space not time. Dimensionally (L/T) * T=L
The universe is expanding at the speed of light in the fourth dimension.

Initially the expansion rate may well have been smaller initially due to the large mass in the smaller universe.
There is no need for "dark energy" to do any thing.
I would like an opportunity to discuss this with you.

Dark matter and dark energy have not been discovered. They have only been postulated because the theoretical math of the orthodox 鈥淪tandard Cosmology鈥� used to describe the universe did not and still does not describe the universe as observed. They amount to what was called in the Cosmology Statement, made by 500+ cosmologists and published in the New Scientist a few years back, as being 鈥渇udge factors鈥�.

There are alternative, credible models of the universe that do not require either dark matter or dark energy but because these are not considered to be in line with orthodox views they are dismissed. I refer you to 鈥淪tarlight, Time and the New Physics鈥� by Dr John Hartnett for an easily understandable account of one example.

So 成人快手, please can we the get the facts right before you report them so as not to mislead.

In response to FVP:

I'm trying to get my head round what you've just said, so I'd appreciate it if you could explain further.

But as I understand your comment - my interpretation of a 'dimension' would be something that has only one variable (e.g. for the standard 3 dimensions: to get movement in just one dimension, then if x & y are constant, then you can move along the z axis).

If the Speed of Light is a constant (which as I understand it, most of physics relies upon that fact), then to say:
4th dimension = Speed of Light * Time between two events
You can effectively rule out the Speed of Light and are left with the Time between two events.

Expect I've missed something, so please could you elaborate....

Hey folks, forget theory for a moment - what we need are *data*! :-)

"The existence of dark energy was established in 1998"

Balderdash. Dark energy is a theory invented to explain another theory, the expansion of the universe, which in turn was invented to explain another theory, so-called cosmological redshifts. Although there is evidence that is consistent with all these theories, none have been proven. Personally, I prefer the "plasma universe" theory, which although it is not as well developed, is also consistent, without the need for dark energy, dark matter and invisible black holes.

The Decadal Survey produced by the National Research Council has listed what it believes the big priorities that should be undertaken in the coming 10 years for American astronomical and astrophysical research. No where among these will you find wasteful expenditure on primitive imperialism and warfare.
The Decadal Document is based on wide consultation; it puts a concept known as WFIRST (Wide-Field Infrared Survey Telescope) as a must-have because humankind must know more about dark energy as well as universe expansion and potential retraction.
WFIRST is actually the second of two major projects; the 1.5-meter space observatory, is planned for injection iton the L2 Lagrangian point.
The first project is called the "Cerro Chajnantor Atacama Telescope". Cerro Chajnantor is the location in Chile where the new telescope is to be constructed. The 25-meter (82-foot) instrument will be charged with witnessing cosmic evolution, and monitoring galactic formation processes.
WFIRST would address broader issues, including undertaking a survey of exoplanets in the Milky Way.
The European version (European Space Agency Mission - Esa) is already in competitive study mode. Esa plans for launch in 2017 and 2018. Europe expects to make a decision on whether to fly Euclid within the next 12 months; the US probably won't be in a make-up-your-mind mode for at least ten years because of current deficits.
Whilst the Decadal Survey indicates it would like to see international cooperation on WFIRST, it is adamant that the US should lead such an important dark energy mission. What? I disagree? European scientists have already stated that a Euclid-type mission is a top priority for them, and the European industry is quite capable to lead the venture.
Anyway, starting in September, bilateral talks will begin between Nasa and Esa.
One thing for sure, the 2000 Decadal Survey placed the 鈥淛ames Webb Space Telescope鈥� (which is due for launch in 2014/2015) as the number 1 issue. This Telescope has cost about $5B (Esa provided the instrumentation and the launch rocket). Neither the US nor Europe can afford to repeat the JWST experience.
I can foresee Europe taking a giant leap forward in space exploration, leaving the United States wallowing in the bloody mayhem of Iraq, Afghanistan, Pakistan, and potentially Iran. There is only so much money to go around, and the American deficit is already so terribly high.

Dark energy is unnecesary.

Hubble Shift is proportional to distance squared, an artfact of observation, as is the CMB.
At the maximum observable distance the sky is black, like the surface of a black hole.

FVP #2.
(MrPahoehoe)

while I'm inclined to agree with you that there "is no need for "dark energy"", I disagree with your description/use of dimensions ("The universe is expanding at the speed of light in the fourth dimension.").

the three/four dimensions referred to do not actually exist themselves, they are simply a notational convenience for locating places and events in an agreed manner.

The community could really benefit from competing efforts - Hubble/NIRSPEC, HERSHEL and WISE are all flying at the same time. Great! they have overlapping but essentially complementary missions. having EUCLID and WFIRST both flying would be very great especially if Euclid was launched a few years ahead. With the surveys it is important to have lots of data spread over time. These mission have relatively short lifetimes- maybe five years on the outside. so.. fly both.. you Euro-types are encouraged to launch first to follow up as the WISE mission soon as possible. by the way, there are likely significant, relatively large objects to be found withing a couple of light years of earth. lets see some of these near neighbors ( closer than proxima or alpha centauri) show up on the longer wave infrared images!

I rather like the idea that we have been exploring space for centuries and have only just discovered the we knew nothing about 90% or so of it.

People forget that the only part of space we actually see is the historical light cone, a razor thin slice of space and time/ and in fact about 10^17:1 or 99.99999..% of the universe is outside it in our FTL shadow. Even our own sun is hidden in the FTL shadow about 8 light minutes away.
As to whether space time is four dimensional that is a pretty complex argument. Minkowski space time is a four dimensional space with time as a dimension, but it is a phase space, that is a notional space. Time is its 'fourth' dimension but it is a notional dimension, Newtonian physics also uses time in the same way for instance graphing distance against time.
The really difficult question is about the reality of time -do the future and past actually have a separate existence or are they simply part of the present? It is a stumbling block that causes problems for all physics not just general relativity but Newtonian mechanics, electronics, and most classical physics.

When you relate scale and time.- In general relativity because time is tied to space by the speed of light- time itself scales with size. - So the universe as a whole (across billions of light years) is only a few seconds old. If time does not scale then neither does the speed of light and general relativity fails on large scales.
Special relativity offers a very different solution because on large scales its inertial frames behave like a classical linear hyperspace and its physics would remain sensible in the FTL region.
Either way it all boils down to another very subtle question - the actual speed of time - the propagation speed of causality itself through space. Generally time must either move at the speed of light or at simultaneous/instantaneous speeds but this is still a very open area (hyperspace type models generally need to allow both).

Quantum mechanics allows something even worse in temporal indeterminacy, this is a place where time itself behaves like a dimension. Although on an extremely small scale if its coherency could be amplified it would allow computation with temporal superpositions/ or at higher energies still a true step into harry potter territory. Who said physics was the most solid of the sciences? :)

Robert Lucien #12.

if one were to have (for the sake of argument) a perfect vacuum, say 1 km3 in size, would time pass/exist in there? isn't time simply an attribute of matter?

Not an easy question to answer jr5512. If there is some inertial field or 'hyperspace' then the answer is positive yes. The same is true of General Relativity because time and distance are tied together.
Quantum mechanics maybe says different, if a space is totally empty and totally shielded from all EM radiation and other energy including heat then no quantum events should happen there and maybe time wouldn't exist or would come to a stop.

Of course the big problem is as always gravity, gravity gets inside anything and is seemingly almost unstoppable, if relativity is correct even a completely curved space time cannot stop gravity. (A completely curved space time is theoretically a barrier to everything even time itself - but not gravity!)