Could future technology test what lies beyond the observable universe?

[adamysy]

TL;DR

Could future technology allow us to test whether anything exists beyond the observable universe? Our current limits may be limits of technology, not necessarily limits of what can be discovered

I have been thinking about a question: Could future technology allow us to test whether anything exists beyond the observable universe?

I think that our inability to detect or test something today does not necessarily mean that it will always be impossible. Our current technology has limits, but those limits may change as science and technology develop.

Perhaps future telescopes, detectors, or completely new methods of observation could give us information that we cannot obtain today. Even if we cannot directly observe beyond the observable universe, maybe we could discover indirect signals or effects that help us understand whether there is anything beyond it.

I am not claiming that something definitely exists beyond the observable universe. I am suggesting that we should keep investigating the question instead of assuming that today's technological limits are permanent.

What do you think? Could future technology give us a way to test this question?

 

[anuttarasammyak]

Area of observable universe is spreading just now. We may be able to find some scientific treasures in new area in future. That seems exciting enough to me.

Time machine could be convenient to observe well enlarged observable universe. We can do the same in current physics by staying near above event horizon of BH in some designed time and coming back.

 

[Bandersnatch]

As was mentioned above, the observable universe is not of a fixed size. The farthest radiation received today - the CMB - arrives from beyond what was the observable universe yesterday, and will tomorrow arrive from beyond our observable universe right now.
You don't need new technology to probe ever father beyond the present-day boundary. Just a bit of patience.

But if you're thinking of employing new techniques towards observing on a given day what will only be observable the day after - then that's hoping one day to be able to receive a signal before it gets here.
It's a bit of a contradiction, that is.

I suppose another way to interpret the question is to ask whether the ever-receding boundary of observability that is the CMB, needs to be such a boundary. Here, new methods of observation could help 'see' beyond the primordial barrier for electromagnetic radiation, perhaps utilising neutrinos instead of photons in our detectors.
You'd still have the boundary constantly recede and encompass more, and still be constrained by the inability to catch a signal that hasn't yet made it here. But in a real sense you'd be able to see beyond what is currently possible - to probe earlier states of the universe, before it stopped being opaque to light.

 

[FactChecker]

Another view:
Anything near the limit of what we "see" now is really the result of our interpretation using a lot of manipulation and modeling. As our models and techniques improve, we will be able to "see" farther.

 

[Herman Trivilino]

TL;DR: Could future technology allow us to test whether anything exists beyond the observable universe? Our current limits may be limits of technology, not necessarily limits of what can be discovered

Could future technology allow us to test whether anything exists beyond the observable universe?

This question seems more about language than technology. When we test for something, and the test is positive, doesn't that mean we've made an observation?

The answer to your question depends on what you mean by beyond the observable universe. If you mean regions of this universe that we are able to observe, then yes. In fact, you don't have to wait for the future. It's happening now. For example, the James Webb telescope is allowing us to see regions we couldn't see before, and continues to do so.

On the other hand, if by beyond the observable universe you mean stuff we cannot ever in principle observe, then no. For example, if we define our universe to be everything can or ever will be able to observe, then stuff outside our universe will never, by definition, ever be observable.

 

[Roberto Pavani]

Observable universe ≠ universe observed today ≠ universe observed in the future.

$\text{Universe observed today} \subset \text{Universe observed in the future} \subseteq \text{Observable universe}$
In a $\Lambda\mathrm{CDM}$ universe, depending on the behaviour of $a(t)$, there may also be regions that will never become observable.

 

[Bandersnatch]

Observable universe ≠ universe observed today

Unless you mean something trivial, like how many galaxies we have pictures of, then that's pretty much what it is. It's the extent of the base of our past light cone. Also synonymous with the particle horizon. That's the standard nomenclature, no?
For observable in principle, we have event horizon.

 

[Roberto Pavani]

I agree regarding the standard nomenclature. My comment was aimed at the OP's question, which suggests that those distinctions may not have been intended.
Otherwise, the question itself would be largely a matter of definition.

 

[Jaime Rudas]

For observable in principle, we have event horizon.

A galaxy currently located 20 billion light-years away lies beyond the event horizon but within our observable universe.

 

[Matterwave]

I agree regarding the standard nomenclature. My comment was aimed at the OP's question, which suggests that those distinctions may not have been intended.
Otherwise, the question itself would be largely a matter of definition.

My personal opinion is switching the definition from the standard one (and in this case, there is a standard one, see e.g. https://en.wikipedia.org/wiki/Observable_universe) to a non standard one like in post #6 is going to lead to more confusion.

 

[Matterwave]

A galaxy currently located 20 billion light-years away lies beyond the event horizon but within our observable universe.

What? What event horizon are you talking about?

 

[Bandersnatch]

A galaxy currently located 20 billion light-years away lies beyond the event horizon but within our observable universe.

Sure. The base of the past light cone of the farthest signals we currently observe is larger in comoving extent than current size of the event horizon. But it wasn't at emission of those signals. There's no contradiction, just comparing different times.

What? What event horizon are you talking about?

If you compare where the EH intersects the 'now' line with how far the 'light cone' reaches out, then the former is closer than the latter - is what Jamie meant.

 

[Jaime Rudas]

What? What event horizon are you talking about?

The cosmological.

 

[Matterwave]

View attachment 374469
If you compare where the EH intersects the 'now' line with how far the 'light cone' reaches out, then the former is closer than the latter - is what Jamie meant.

Thank you for the graph! It is clear.

 

[Matterwave]

The cosmological.

Fair enough. But what was your point?

 

[Jaime Rudas]

Fair enough. But what was your point?

It seemed to me that in post #7, @Bandersnatch was suggesting the event horizon had some connection to the limits of the observable universe. My point is that there is no such connection.

 

[Jaime Rudas]

It seemed to me that in post #7, @Bandersnatch was suggesting the event horizon had some connection to the limits of the observable universe. My point is that there is no such connection.

For the sake of clarity regarding terms:

The particle horizon is the current distance to the farthest comoving object from which, in principle, we could be receiving a signal today.

The cosmological event horizon is the current distance to the farthest comoving object that, in principle, could eventually receive a signal emitted by us today.

 

[Matterwave]

It seemed to me that in post #7, @Bandersnatch was suggesting the event horizon had some connection to the limits of the observable universe. My point is that there is no such connection.

I see, fair enough. I don't think there's any disagreement. I read @Bandersnatch as saying the same thing ("in principle"). But it's good we cleared up the language. :)

 

[Jaime Rudas]

I don't think there's any disagreement. I read @Bandersnatch as saying the same thing ("in principle").

The disagreement lies in the fact that @Bandersnatch seems to be linking in some way the observable universe to the event horizon, whereas I only link it to the particle horizon.

 

[Herman Trivilino]

A galaxy currently located 20 billion light-years away lies beyond the event horizon but within our observable universe.

So it's too far away to observe but it's within our observable universe?

How are you defining observable universe?

 

[loop quantum gravity]

TL;DR: Could future technology allow us to test whether anything exists beyond the observable universe? Our current limits may be limits of technology, not necessarily limits of what can be discovered

I have been thinking about a question: Could future technology allow us to test whether anything exists beyond the observable universe?

I think that our inability to detect or test something today does not necessarily mean that it will always be impossible. Our current technology has limits, but those limits may change as science and technology develop.

Perhaps future telescopes, detectors, or completely new methods of observation could give us information that we cannot obtain today. Even if we cannot directly observe beyond the observable universe, maybe we could discover indirect signals or effects that help us understand whether there is anything beyond it.

I am not claiming that something definitely exists beyond the observable universe. I am suggesting that we should keep investigating the question instead of assuming that today's technological limits are permanent.

What do you think? Could future technology give us a way to test this question?

No. There will always be something beyond what we can observe in experiment. It's inherent in every experiment. At least it's good to think that as we proceed with technology the resolution becomes even finer and finer, but you can't approach the perfect and exact resolution in a finite time steps.

So there will always be more experiments to do and theories to ponder, some can be ruled out experimentally, and some won't even be wrong...

 

[Bandersnatch]

linking in some way the observable universe to the event horizon, whereas I only link it to the particle horizon.

The particle horizon is the mirror image of our past light cone. That's the currently observable universe, and what you're focusing on. I don't think there's any disagreement here.
The past light cone, as can be seen on the conformal graph, is bounded by the event horizon, which is the maximum observable region of space time. The particle horizon in the infinite future is the mirror image of the event horizon. Hence this is the in-principle observable universe.

 

[Jaime Rudas]

So it's too far away to observe but it's within our observable universe?

We certainly can observe a galaxy that is currently 20 billion light-years away. In fact, the light we see from that galaxy has a redshift of nearly 3.

How are you defining observable universe?

The observable universe is everything within the particle horizon.

 

[Jaime Rudas]

The particle horizon is the mirror image of our past light cone. That's the currently observable universe, and what you're focusing on. I don't think there's any disagreement here.

I agree.

The past light cone, as can be seen on the conformal graph, is bounded by the event horizon, which is the maximum observable region of space time.

I don't understand what you mean when you say it "is bounded." And I don't understand it because I don't see them coinciding.

The particle horizon in the infinite future is the mirror image of the event horizon. Hence this is the in-principle observable universe.

I don't see why the fact that they are mirror images implies that this is "the in-principle universe observable."

 

[Matterwave]

So it's too far away to observe but it's within our observable universe?

How are you defining observable universe?

The graphic (and commentary) in post #12 should help.

The cosmic event horizon assumes an accelerated expansion so that even a world line that reaches conformal infinity (the infinitely far future) is causally disconnected from certain events. A galaxy that is 20Glyr comoving distance "now" (defined by the family of observers that see an isotropic CMBR) could not send us a signal. They are beyond the cosmic event horizon, assuming the dark energy is a true cosmological constant (doesn't change with time). A lot of this was not elucidated at the beginning of the discussion unfortunately.

 

[Roberto Pavani]

Doesn't this requires that $\int_{t_0}^{\infty}\frac{dt}{a(t)}$ to be finite ?
Acceleration itself doesn't allow this.
As an example:

Suppose $a''(t)>0$ but $a(t)=t\log(1+t)$

gives:

$\int_{t_0}^{\infty}\frac{dt}{a(t)} =\int_{t_0}^{\infty}\frac{dt}{t\log (1+t)} =\infty.$

In this example, there is no finite cosmic event horizon.

 

[Matterwave]

Doesn't this requires that $\int_{t_0}^{\infty}\frac{dt}{a(t)}$ to be finite ?
Acceleration itself doesn't allow this.
As an example:

Suppose $a''(t)>0$ but $a(t)=t\log(1+t)$

gives:

$\int_{t_0}^{\infty}\frac{dt}{a(t)} =\int_{t_0}^{\infty}\frac{dt}{t\log (1+t)} =\infty.$

In this example, there is no finite cosmic event horizon.

Are you talking to me?

Note this sentence in my post #25:

They are beyond the cosmic event horizon, assuming the dark energy is a true cosmological constant (doesn't change with time).

Try your integral but this time use an actual cosmological constant. What is the form of $a(t)$ in that case?

 

[Roberto Pavani]

My fault. I didn't realize you meant a constant "cosmological constant".