Raymond Tallis: Time Travel and Other Myths about Time

Intuitively I think it must be in this way. (I’m sure Einstein privately must have thought the same)

The video gets into this...

I finally understand what you're saying. Here's the Schwarzschild metric, which is a solution for the gravitational field around stars, with the time component in bold. It bears the opposite sign compared to the almost identical radial component (the star is modeled as a sphere). So indeed, thinking of 4D spacetime as a simple generalization of 3D space can be somewhat misleading.



Schwarzschild metric

Right, by generalising a familiar mathematical idea but then talking about it using the original terminology, you can mislead people badly.

More generally, as a kid, I found the idea of curved space intriguing. Later I came to realise that ideas like that can be so 'tasty' that they lead science horribly off-course. I mean is it reasonable to argue that physical matter warps the very coordinate system used to measure it? There is a valid use for such coordinate systems - e.g. in the physics of deformable media such as rubber. It is when such mathematical tricks are pulled into the heart of physics that I get worried.

Science used to take seriously the fact that every formula had a finite accuracy and a finite range of applicability. Those wonderfully simple gas laws break down at high densities, chemistry is full of approximate, empiricle concepts, but everyone accepts that this is so because we know about the underlying atomic/molecular layer.

I suspect physics goes astray by not realising that when you expand from the scale of one solar system to the scale of a whole galaxy there may be a slew of new phenomena ready to mess up the calculations. Thus galaxies don't seem to rotate according to GR, and the response is to invent a horrible kludge - dark matter - to solve that problem.

Within the solar system Newtonian Gravity works to high accuracy, there is barely any reason to introduce the hugely complicated GR. When you look at the galactic scale it fails badly without applying a huge kludge, doesn't that make you a bit queasy about the validity of GR?

David

Right, by generalising a familiar mathematical idea but then talking about it using the original terminology, you can mislead people badly.

More generally, as a kid, I found the idea of curved space intriguing. Later I came to realise that ideas like that can be so 'tasty' that they lead science horribly off-course. I mean is it reasonable to argue that physical matter warps the very coordinate system used to measure it? There is a valid use for such coordinate systems - e.g. in the physics of deformable media such as rubber. It is when such mathematical tricks are pulled into the heart of physics that I get worried.

Science used to take seriously the fact that every formula had a finite accuracy and a finite range of applicability. Those wonderfully simple gas laws break down at high densities, chemistry is full of approximate, empiricle concepts, but everyone accepts that this is so because we know about the underlying atomic/molecular layer.

I suspect physics goes astray by not realising that when you expand from the scale of one solar system to the scale of a whole galaxy there may be a slew of new phenomena ready to mess up the calculations. Thus galaxies don't seem to rotate according to GR, and the response is to invent a horrible kludge - dark matter - to solve that problem.

Within the solar system Newtonian Gravity works to high accuracy, there is barely any reason to introduce the hugely complicated GR. When you look at the galactic scale it fails badly without applying a huge kludge, doesn't that make you a bit queasy about the validity of GR?

David

It's only with General Relativity that we can fully account for the gravitational motion of Mercury around the Sun. Concerning the geometry of space, Einstein himself once wrote, 'It is wrong to think that "geometrization" is something essential. It is only a kind of crutch for the finding of numerical laws. Whether one links "geometrical" intuitions with a theory is a ... private matter.' Therefore, it's reasonable to assume that Einstein did not regard the geometrization of gravity as an indisputable physical reality. Nonetheless, it is a tremendously successful mathematical framework for calculating celestial motion, at least within the local galactic neighborhood.

With that said I suspect that you are right that there is no dark matter and dark energy and so forth.

I’m not convinced about physical realism. I lean very much towards an empiricist view of science. I don’t think we will ever know any objective truth below the layers of experiments and mathematics.

it is a tremendously successful mathematical framework for calculating celestial motion, at least within the local galactic neighborhood.

How is that consistent with the fact that dark matter is needed to explain the rotation of galaxies (including presumably our own)?

David

How is that consistent with the fact that dark matter is needed to explain the rotation of galaxies (including presumably our own)?

David

With “local” I meant star systems and not greater scales.

What “local” I meant star systems and not greater scales.

Ah - now we seem to be converging!

It's only with General Relativity that we can fully account for the gravitational motion of Mercury around the Sun. Concerning the geometry of space, Einstein himself once wrote, 'It is wrong to think that "geometrization" is something essential. It is only a kind of crutch for the finding of numerical laws. Whether one links "geometrical" intuitions with a theory is a ... private matter.' Therefore, it's reasonable to assume that Einstein did not regard the geometrization of gravity as an indisputable physical reality. Nonetheless, it is a tremendously successful mathematical framework for calculating celestial motion, at least within the local galactic neighborhood.

Einstein's views on "geometrization" are very interesting - I wish he were around now to comment on the way things have developed!

I have seen suggestions that the bending of starlight around the sun (visible when there is a solar eclipse) can be counted for by a modified SR that simply assumes that light slows down in a gravitational field causing refraction - just as it does in other media!

My impression is that for any important scientific theory there is a period of a few years in which it is considered fair game to attack it, after which others have used the theory in their own work and there is then enormous reluctance to consider other alternatives. Logically science should only become settled after decades or even centuries have passed.

By now, even if someone did come up with a modification of SR that accounts for the precession of Mercury's orbit, I wonder if he could even get it published!

GR is inconsistent with QM, and it seems to me that if just one theory is wrong, it is more likely to be GR. I mean QM has been tested in a whole variety of ways in actual experiments (as opposed to observations) where you can vary parameters such as the electric/magnetic field strength.

Of course if GR were to fall, black holes, the big bang, and other concepts would also be in doubt. I know black holes have supposedly been detected, but without black holes, is it likely the actual observations would remain unexplained for long?

If I sound very cynical about modern science, that is because I am!

David

Nbtruthman,

Do you have a good link to a discussion about the results of the JWST? There seem to be some YouTube videos, but these trivialise the question too much.

I know there have been far more galaxies found at extreme red shifts, but are we getting close to the point where galaxies might be visible before the big bang? Indeed, would we ever know about such galaxies because presumably the red shifts would tend to infinity as we approach the supposed time of the big bang?

At what point (if ever) will it be absolutely clear that JWST has invalidated the Big Bang model?

David

Nbtruthman,

Do you have a good link to a discussion about the results of the JWST? There seem to be some YouTube videos, but these trivialise the question too much.

I know there have been far more galaxies found at extreme red shifts, but are we getting close to the point where galaxies might be visible before the big bang? Indeed, would we ever know about such galaxies because presumably the red shifts would tend to infinity as we approach the supposed time of the big bang?

At what point (if ever) will it be absolutely clear that JWST has invalidated the Big Bang model?

David

I don't know that we can ever be absolutely certain of anything. But on this particular claim, I am a skeptic. I haven't extensively studied this controversy, but I have the tentative opinion that it boils down to hype and poor science journalism. Galaxy formation theories for the very early Universe may have to be changed, and the exact age of the Big Bang may have to be revised upward a little, but not the actual existence of the Big Bang as the beginning of our Universe. There are certainly a number of important scientific issues in cosmology and other disciplines where the accepted "consensus" is probably wrong, but I don't think the Big Bang is one of them. Of course there may be other factors and arguments that I haven't become acquainted with that could change this opinion, but that is where I stand right now.

I hadn't searched the Internet for discussion blogs on this, but a cursory look found one site (Quora, at https://www.quora.com/If-the-JWST-proves...ry-in-part) which amongst some junk included multiple half-way decent quality posts. These posts date back some, but I think they sum up a considerable consensus that that is what this really is. The following is an example of what seems to me one of the better ones, except for the gratuitous insults to all conspiracy theorists and Intelligent Design proponents:

From Krister Sundelin

Question: Scientists have recently discovered six ancient galaxies by JWST that are about the age of the universe that we know which is approximately 14 billion years old, would that prove that the Big Bang theory and how the universe started theories wrong?

Ans: Contrary to what every sensationalist pop sci journalist, conspiracy theorist and creationist seem to think, it would not prove that the Big Bang theory is wrong. The evidence for the Big Bang theory is too strong, including the expansion rate of the universe and the cosmic microwave background. That evidence didn’t go away just because some galaxies have higher redshift than expected.

So what is going on here?

Obviously, the first option is that our model for redshift is wrong, or more likely, incomplete at extreme distances. For instance, our models may not be taking the denser early universe and therefore gravitational redshift into account. This is highly likely, since before JWST, we did not have any data for redshift higher than z=11.

The second option is that there is something wrong with the method used to calculate the age of the universe from the cosmic microwave background or the expansion rate of the universe. This is also likely, since the measurement of the expansion rate measures differs between microwave background and supernovae type 1A.

The third option is that there is a systemic error in the measurement of the extreme redshift of those galaxies. This is not that likely, since JWST was extensively tested before launched. But it must still be investigated.

The fourth option is that our theories of galaxy formation in the early universe is wrong, and that galaxies formed a lot earlier than we think – closer to 100 million years (0.1 billion years) after the Big Bang than 500 million years after the Big Bang. This is also pretty likely, since again we did not have any observations earlier than 500 million years after the bang pre-JWST.

Any or all of these options – and more – may introduce an error into the measurement or the analysis of the data. So what we need to do now is to analyse the data, come up with models which work better, make predictions from those models and test those against future observations from JWST.

So as usual, more caution and more study and above all, more observations are needed.

Nbtruthman,

I tried to join that group, but GOOGLE just seemed to hang!

Maybe you or @sbu know the answer.

Assuming 'standard cosmology' if a galaxy has some particular redshift R, then that will be translated into a corresponding distance away, and hence distance back in time.

Is there a formula F(R) that translates a redshift into a time since big bang?

I'm guessing that F will become singular at the Big Bang, so it will never be possible to discover galaxies further back in time than the BB.

I.E. don't you end up using standard cosmology to extract the distance and age of the galaxy - so it is logically impossible to go back before the BB under those assumptions?

David

I.E. don't you end up using standard cosmology to extract the distance and age of the galaxy - so it is logically impossible to go back before the BB under those assumptions?

David

Exactly. When we use standard cosmology (including general relativity) to interpret JWST data, we're indeed working under the assumption that the universe began with the Big Bang, and thus we can't observe anything before that event. It requires tons of existing theory to interprete the images. JWST - it is after all just a machine capturing pictures.

So JWST can’t disprove Big Bang by it self but it can still prove existing theories regarding galaxy formation inadequate and probably other stuff as well.