Is reality really “nothing but a hallucination”?

Question

I asked this a few minutes ago on physics.stackexchange and they redirected me here

This question relates to the premise put forth in this TED talk, that reality is nothing but a shared hallucination:

http://www.openculture.com/2017/08/reality-is-nothing-but-a-hallucination-a-mind-bending-crash-course-on-the-neuroscience-of-consciousness.html

I am totally on board with the idea that our senses often give us a skewed, warped, and possibly wrong idea about what we are perceiving.

My quibble / question is with the "nothing" part of "nothing but a shared hallucination"

For example, take a large fish tank that holds 1000 gallons of water. I understand that a crafty magician could possibly set up a sensatory trick with this. But barring that, my reality is that lifting this fish tank is not something that one human being - even the strongest human in the world - can do alone, given the parameters and variations on the human body.

The mass of this fish tank seems to be an invariant in the universe, no matter what hallucinated perceptions I/you/we have. The mass of this fish tank, it seems to me, is "real". And that's what I don't understand about "reality is nothing but a hallucination"

Can you help me reconcile my dilemma?

Answer 1

I didn't watch the TED talk, but here are three things about your question.

First, I don't think there's any dilemma here. According to the hallucination argument, there is no mass -- all there is is your sensations: you have a sensation of weight, a sensation of touch, etc., but there's nothing real (according to this argument) beyond those sensations.

Second, here's a way to argue against the claim the everything is a hallucination. The hallucination claim is similar to other skeptical arguments, such as Descartes' dream argument in the Meditations, that everything might be just a dream. Gilbert Ryle famously criticized such arguments:

A country which had no coinage would offer no scope to counterfeiters. There would be nothing for them to manufacture or pass counterfeits of. [...]

In a country where there is a coinage, false coins can be manufactured and passed; and an ordinary citizen, unable to tell which were false and which were genuine coins, might become suspicious of the genuineness of any particular coin that he received. But however general his suspicions might be, there remains one proposition which he cannot entertain, the proposition, namely, that it is possible that all coins are counterfeits. For there must be an answer to the question ‘Counterfeits of what?’ (Dilemmas, pp. 94-95)

According to this argument, it makes no sense to say that everything is a hallucination, since the concept of hallucination presupposes a concept of reality. (Just as the concept of the fake coin presupposes the concept of a genuine one.)

Third, the idea that everything is a shared hallucination doesn't make too much sense. Shared with whom? If it's shared with other people then not everything is a hallucination since there are at least other people.

Answer 2

It is a well-established empirical fact that physical measurements made by two different observers, although not numerically equal, are related by means of well-defined mathematical transformation laws. That is, if we have the measurements of one observer A, and we know its position, orientation and relative motion with respect to a second observer B, we can predict what the observer B would measure if we know what was measured by observer A (I explicitly exclude cases where quantum entanglement plays a central role).

Therefore, if we reject the solipsistic assumption, it seems that there is a very subtle relationship between what is observed by different observers, if it were a collective hallucination we could hardly find such consistency in the measurements of physical phenomena.

This intersubjectivity of physical measurements could therefore be interpreted as an indication that there is an objective reality outside the minds of the observers who observe the physical world (otherwise, it does not seem easy to explain the precise correlations between their physical measurements).