Description
Crosswalk supplied same-epoch physical and comoving lengths using a scale factor.
Cosmological quantities depend on scale factor, redshift, distance definition and the dimensionless Hubble parameter h. Proper and comoving distances differ at a specified epoch, and h-scaled units differ from the dimensional Hubble constant. A scalar rescaling or model contribution preserves supplied conventions without fitting a cosmology or inferring an observed distance.
Crosswalk supplied same-epoch physical and comoving lengths using a scale factor.
When to use this tool
Use Cosmology Distance Physical Comoving Label when you already have distance, scaleFactor, inputConvention and need to crosswalk supplied same-epoch physical and comoving lengths using a scale factor.
How to use the tool and how it works
- Enter distance, scaleFactor, inputConvention. Use the units and conventions below.
- Run the tool. Correct any format, range, or cross-field input error before interpreting the output.
- Read physicalDistance, comovingDistance. Use the output convention below.
Require distance>=0, scaleFactor>0 and convention physical/comoving; physical=a*comoving, dividing by a for physical input and multiplying for comoving input.1
Proper separation at a stated epoch differs from comoving separation by the scale factor. This is separate from luminosity and angular-diameter distance.2
| Input field | Meaning and units | Accepted input |
|---|---|---|
| distance | Distance | Required. Finite number; minimum 0. |
| scaleFactor | Positive dimensionless scale factor at the same epoch as both distance conventions; values above one are accepted. | Required. Finite number; strictly above 0. |
| inputConvention | Input Convention | Required. Text; one of "physical", "comoving"; maximum UTF-16 length 8192. |
| Output field | Interpretation | Returned shape |
|---|---|---|
| physicalDistance | Proper distance at that epoch, equal to scaleFactor*comovingDistance in the same length unit. | Required. Finite number. |
| comovingDistance | Comoving Distance | Required. Finite number. |
{
"input": {
"distance": 100,
"scaleFactor": 0.5,
"inputConvention": "comoving"
},
"output": {
"physicalDistance": 50,
"comovingDistance": 100
}
}Limitations and assumptions
- Scale-factor normalization and epoch are supplied. This is not a cosmological distance integral or an angular-diameter/luminosity distance conversion; future a>1 is accepted.
- Inputs must satisfy both the field types and the cross-field conditions above. Invalid input causes an error; a successful false flag or documented placeholder is a different result.
- Numeric calculations use binary floating point unless exact decimal-integer arithmetic is explicitly stated. No hidden measurement tolerance or decimal rounding is added; nonfinite or out-of-contract results are rejected. Numeric signed-zero results are exported as zero.
Alternative or Complementary methods
Use the complete cosmological model and its parameter, epoch and unit definitions for a physical inference. Review redshift, distance, lensing and spectrum conventions before combining these local terms; they do not perform line-of-sight integration, parameter estimation or uncertainty analysis.
References
Similar or alternative tools
- Comoving Volume H Cubed Unit Pair
Remove an inverse-cubic h scale from a supplied volume.
- Cosmological Time Dilation Interval Pair
Apply a supplied cosmological redshift time-dilation factor.