Recording space-time

[johnfp]

I know a photograph records a slice of time. But it lacks a whole dimension if you believe time is the 4th dimension.

Now a hologram is truly a recorder of a slice of time (I will explain slice soon) while also recording the first three dimensions of volumetric space.

If you take a transmission hologram that was made with a laser that has a long coherence length and set it up so you can see the object (virtual image) you can actual look past the object and see all the optics on the table. If you get really close to the hologram (but be careful not to let the laser light enter your eyes) and look extremely right and left of the object you would be surprised at what you can see. Blockers, optics, part of the table top, things off the table, the walls etc., and these can be meters deep.

Now the reason I call it a slice of time is because a hologram, like a photo, needs a length of exposure, exposure time. So if the exposure was 15 seconds long then you are recording 15 seconds worth of space-time. This is particularly evident when you see that one blocker or object not on the table but on the counter next to the vibration isolation table, has a series of black lines on it. You actually recorded its resonance or movement in that slice of time. Count the number of black lines and you can tell how much it moved (interferometry).

So the next time you have access to a very deep transmission hologram, take a good look inside of it (again watch those eyeballs) and awe at the recording power of the hologram. Truly a recording of all 4 dimensions, space-time!

[UncleAl]

The last Uncle Al heard the EM spectrum extended from fractional Hz to reciprocal Planck time. A hologram records an essentially monochromatic view - one very narrow frequency window probing a small subset of optical transitions. How much of a "slice of spacetime" overall can that be?

[steve 9]

Originally Posted by johnfp

I know a photograph records a slice of time. But it lacks a whole dimension if you believe time is the 4th dimension.

Now a hologram is truly a recorder of a slice of time (I will explain slice soon) while also recording the first three dimensions of volumetric space.

If you take a transmission hologram that was made with a laser that has a long coherence length and set it up so you can see the object (virtual image) you can actual look past the object and see all the optics on the table. If you get really close to the hologram (but be careful not to let the laser light enter your eyes) and look extremely right and left of the object you would be surprised at what you can see. Blockers, optics, part of the table top, things off the table, the walls etc., and these can be meters deep.

Now the reason I call it a slice of time is because a hologram, like a photo, needs a length of exposure, exposure time. So if the exposure was 15 seconds long then you are recording 15 seconds worth of space-time. This is particularly evident when you see that one blocker or object not on the table but on the counter next to the vibration isolation table, has a series of black lines on it. You actually recorded its resonance or movement in that slice of time. Count the number of black lines and you can tell how much it moved (interferometry).

So the next time you have access to a very deep transmission hologram, take a good look inside of it (again watch those eyeballs) and awe at the recording power of the hologram. Truly a recording of all 4 dimensions, space-time!

Tell me, what evidence do you have that states time or space are real physical things?

[steve 9]

Originally Posted by UncleAl

The last Uncle Al heard the EM spectrum extended from fractional Hz to reciprocal Planck time. A hologram records an essentially monochromatic view - one very narrow frequency window probing a small subset of optical transitions. How much of a "slice of spacetime" overall can that be?

Do you think that this thing called space-time is a real physical thing? If so, then what physical evidence has lead you to believe that space-time is a real physical thing?

[johnfp]

Originally Posted by UncleAl

The last Uncle Al heard the EM spectrum extended from fractional Hz to reciprocal Planck time. A hologram records an essentially monochromatic view - one very narrow frequency window probing a small subset of optical transitions. How much of a "slice of spacetime" overall can that be?

Does space time not exist for a single slice of EM radiation?
Does space time not exist for a single photon?

Or does the full set of EM radiation need to be present/considered for space-time to exist?

Very interesting questions.

I have to continue to believe the hologram still has the ability to record a slice of space-time, space being 3 dimensions and time being the minute changes in time as stated.

But like you say, how big a slice is that? If it were all encompassing, would that not be another reality?

[kalexia]

Originally Posted by steve 9

Tell me, what evidence do you have that states time or space are real physical things?

Why does everything have to be a real physical thing? We know time exists.

[johnfp]

Well, keeping within the scope of holography, one can prove time exists with physical evidence.

When one makes a hologram we are recording a set of standing waves. If there were no time, then movement would not be an issue. But because time exists and movement of one of the beams relative to the other beam causes a change in phase of the one beam relative to the other, those standing wave patterns move. As a result, we get bands of destructive interference commonly seen and used in non destructive holographic interferometry.

Because time is a measuring system used to sequence events, when those events are recorded sequentially, does that not prove time, as we define it, exists?

So I am not sure what you meant my "no physical evidence". Look at the frames of a movie. Are they all the same? Does not time need to exist for the frames to be a sequential set of events? Is that not physical evidence that time, as we define it, has to exist?

[johnfp]

And space can be proven by simply trying to place two solid objects in the same space. Since we can not, then space has to exist and the first object must be fully occupying that space. No?

[kalexia]

I absolutely agree with what you are saying. I know there are many instances and examples where it is clear that time and space exist and I also believe that they, like you say, count as physical evidence. I just wasn't sure why Steve9 could not see time and space as physical things.

Originally Posted by steve 9

Do you think that this thing called space-time is a real physical thing? If so, then what physical evidence has lead you to believe that space-time is a real physical thing?

[Qfwfq]

Holography can be boiled down to an application of Dirichlet's principle:

Originally Posted by UncleAl

A hologram records an essentially monochromatic view

The essential thing isn't monochromaticity but coherence, a long enough coherence time for the film exposure. It just unfortunately happens that the only currently known sources fulfilling this requisite are lasers and that these are monochromatic. If there hypothetically were such a thing as a white laser, with as broad a spectrum as you please, Dirichlet would tell you colour holography ought to work, except for the detail that you would have to replace the emulsion with something suitable to the purpose.

Originally Posted by UncleAl

How much of a "slice of spacetime" overall can that be?

You appear to be arguing about the Fourier transform but I wouldn't say that it's relevant. Even recording the full and continuous spectrum at each point of the surface would hardly give you a motion hologram, you'd also need an ideal white laser equivalent to a perfect Dirac delta of EM radiation... Perhaps they'll have it in the next sequel of Star Trek? I don't believe our eyes would perceive it that way anyhow, we see the spectrum as colour rather than as time dependence.