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Ranku
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The universe is observed to be flat. This is due to its energy density, and also due to purported inflation. How do we distinguish between the contribution of each toward flatness?
Ranku said:The universe is observed to be flat. This is due to its energy density, and also due to purported inflation. How do we distinguish between the contribution of each toward flatness?
marcus said:If I understand what you have in mind, then there is no need to distinguish because there are two types of causation. The two causes are not mutually exclusive.
The energy density of what, precisely? Different sorts of energy densities do different things. Inflation is proposed as a particular sort of field that behaves at early times very much like vacuum energy, and that sort of energy tends to dilute away curvature.Ranku said:So flatness itself is no proof of the occurance of inflation; flatness could well have been caused by the energy density alone.
Well, it doesn't really. It comes sort of close to ruling out a perfectly-flat primordial power spectrum, which isn't really an expected feature in inflationary models anyway. Basically, because inflation has to end, we expect there to be some deviation from a perfectly-flat primordial power spectrum. A perfectly-flat primordial power spectrum was a pre-inflation idea that doesn't really have any physical basis.Ranku said:And what is it that I hear about WMAP data ruling out the simplest inflationary models?
Chalnoth said:The energy density of what, precisely?
Those energy densities as measured today would not have caused the universe to approach flatness in the past. Before about 5 billion years ago, the trend would have been away from flatness in that situation.Ranku said:Energy density of dark energy + dark matter + regular matter + radiation
Chalnoth said:Those energy densities as measured today would not have caused the universe to approach flatness in the past. Before about 5 billion years ago, the trend would have been away from flatness in that situation.
The change in curvature due to dark energy over that time has been extremely minimal. In order for us to be unable to measure any deviation from flatness at the current time, our universe had to be massively, absurdly flat in the very early universe (for example, when baryogenesis was occurring).Ranku said:Do we know if the universe was flat before 5 Gy ago, i.e., before it started expanding acceleratively due to dark energy? And if it was flat before 5 Gy ago, would that not be irrefutable proof of inflation? Or can the universe be flat before 5 Gy ago even without inflation?
The change in curvature due to dark energy over that time has been extremely minimal. In order for us to be unable to measure any deviation from flatness at the current time, our universe had to be massively, absurdly flat in the very early universe (for example, when baryogenesis was occurring).
Ranku said:Sorry, I'm not getting any of this :(. Could you just tell me if there is observational evidence that the universe was flat before 5 Gyr?
And if so, can we distinguish between if that flatness at that time was caused by dark energy or inflation?
If there is no observational evidence of deviation from flatness now, then there certainly isn't any evidence of any deviation as of 5 Gyr ago.Ranku said:Sorry, I'm not getting any of this :(. Could you just tell me if there is observational evidence that the universe was flat before 5 Gyr? And if so, can we distinguish between if that flatness at that time was caused by dark energy or inflation?
Huh? In what sense does it make the problem worse? It doesn't solve the problem, granted, but it does make the universe flatter as time goes on.twofish-quant said:Dark energy doesn't help this. It makes the problem even worse.
Chalnoth said:Huh? In what sense does it make the problem worse? It doesn't solve the problem, granted, but it does make the universe flatter as time goes on.
Flatness refers to the condition of a surface or object being completely level or smooth. It is important in many fields of science and engineering, as well as in everyday life, because it affects the accuracy and precision of measurements and the functionality of many objects and structures.
Flatness can be measured using various tools such as a straight edge, surface plate, or optical flat. It is typically expressed as the maximum distance between the highest and lowest points on the surface, often referred to as the flatness tolerance. This tolerance is usually given in units of length (e.g. millimeters) and is determined based on the specific application or industry standards.
Flatness errors can be caused by various factors such as manufacturing processes, material properties, and environmental conditions. They can be minimized by using proper techniques and equipment during production, selecting suitable materials, and controlling environmental factors such as temperature and humidity.
Flatness refers specifically to the overall levelness of a surface, while straightness refers to the linearity of a surface or object. Parallelism, on the other hand, describes the relationship between two or more surfaces that are supposed to be parallel to each other. Flatness, straightness, and parallelism are all important characteristics in different applications and should be measured and controlled accordingly.
Flatness is a crucial aspect of an object's shape and geometry. It determines how well the object conforms to a desired form or specification. For example, a flat surface is necessary for a door to fit properly into its frame, and a flat mirror is required for accurate reflection. In addition, flatness can also affect other properties of an object, such as its strength and stability.