Questioning Hubble's Law: Does the Expanding Universe Theory Hold Up?

[khurramc]

The Hubble's Law is based on empirical evidence that those objects further from us are moving away from us proportionate to their distance from us.

My question is that the further we look back the further we look back in time. And so, why is that when we see further, and notice objects moving away faster, do we state that the universe is expanding?

I mean even in a universe that was not expanding, wouldn't objects back in time (and therefore further from us) be moving faster than objects nearer to us just because of the speed of light and the fact that our view further into the universe is but a picture of how the universe was in the past?

I understand that objects further away from us are moving away faster. I am just concerned with the fact, that would that not be natural if you were looking back in time to an explosion slowing down and a universe not expanding? Since even if expansion was slowing down, we would notice that objects further way would depict speeds of expansion in the past, while objects closer would reflect speeds closer to the present. Therefore, if the the expansion was slowing down, wouldn't objects further depict a faster speed than objects closer?

Any explanations to my query would be much appreciated.
Regards
Khurram Chaudhry

 

[mfb]

If the universe would not expand, these objects would not move away at all, apart from random velocities due to gravitational influence from objects nearby.

An explosion in space violates the observation that the universe looks the same everywhere, together with some more technical details. It is an expansion of space itself, not an expansion of matter in space.

The chance in the expansion rate (which is not the same as the expansion rate!) is a different issue. Compared to a constant expansion rate, you are right that objects far away are not as fast as you would expect. However, space was always expanding, so they are still more redshifted than objects closer to us.

 

[Chalnoth]

The Hubble's Law is based on empirical evidence that those objects further from us are moving away from us proportionate to their distance from us.

My question is that the further we look back the further we look back in time. And so, why is that when we see further, and notice objects moving away faster, do we state that the universe is expanding?

I mean even in a universe that was not expanding, wouldn't objects back in time (and therefore further from us) be moving faster than objects nearer to us just because of the speed of light and the fact that our view further into the universe is but a picture of how the universe was in the past?

I understand that objects further away from us are moving away faster. I am just concerned with the fact, that would that not be natural if you were looking back in time to an explosion slowing down and a universe not expanding? Since even if expansion was slowing down, we would notice that objects further way would depict speeds of expansion in the past, while objects closer would reflect speeds closer to the present. Therefore, if the the expansion was slowing down, wouldn't objects further depict a faster speed than objects closer?

Any explanations to my query would be much appreciated.
Regards
Khurram Chaudhry

A more accurate way of talking about the redshift is that when the universe expands, the wavelength of photons is expanded as well. So if we observe an object and the photons from that object have wavelengths that have doubled, then we know that the universe has expanded by a factor of two in the interim since that light was first emitted. The universe has expanded more for further-away objects, and so we see further-away objects as having higher redshifts.

A less accurate but possibly more intuitive way of thinking about it is to just ignore the weirdness of General Relativity and consider redshift to be a measure of velocity of the far-away object. In an expanding universe, the recession velocity of an object is given by the Hubble expansion rate times that object's distance (i.e. $v = Hd$). So having a higher recession velocity (measured via redshift) in the past doesn't necessarily mean that H was higher in the past: in fact, H could, in principle, be lower and we'd still see further-away objects having higher velocities (as long as the reduction in H is smaller than the increase in d). In practice, though, H has decreased over time for the duration of our observable universe's existence.

 

[Naty1]

I understand that objects further away from us are moving away faster. I am just concerned with the fact, that would that not be natural if you were looking back in time to an explosion slowing down and a universe not expanding? Since even if expansion was slowing down, we would notice that objects further way would depict speeds of expansion in the past, while objects closer would reflect speeds closer to the present.

That's logical, as far as it goes, and I would not be surprised if some scientists perhaps started out from that perspective...but as noted above, we have observation evidence that is contrary to those assumptions...so scientists had to develop a different model that matches observations. That model is the FLRW model with lambda CDM parameters.

 

[sardar]

I can understand your concern and curiosity about the validity of Hubble's Law in relation to the expanding universe theory. However, it is important to note that Hubble's Law is not solely based on the observation of objects moving away from us at a faster rate as we look further into the universe. It is also supported by other evidence, such as the redshift of light from distant galaxies, which indicates that they are moving away from us and the universe is expanding.

Additionally, the concept of the universe expanding is not just based on the observation of objects moving away from us, but also on the theoretical framework of the Big Bang theory. This theory suggests that the universe began as a singularity and has been expanding ever since. The observation of objects moving away from us at a faster rate as we look further back in time is consistent with this theory.

Furthermore, your concern about objects further away depicting faster speeds even in a non-expanding universe is not entirely accurate. In a non-expanding universe, the speed of light is constant and therefore objects further away would not appear to be moving faster just because of the time it takes for light to reach us. This is because the speed of light is already factored into the calculation of the object's distance and velocity.

In conclusion, while it is important to question and critically analyze scientific theories, it is also important to consider all the evidence and theoretical frameworks that support them. Hubble's Law, along with other evidence, provides strong support for the expanding universe theory and has been widely accepted by the scientific community.